There is no exact spec for the manifold vacuum. It will vary, depending on idle speed, ignition timing, fuel mixture, type of camshaft, exhaust system, compression, and many other factors. The normal range will be somewhere between 18 and 21 inches.
It may be possible to increase the vacuum by advancing the timing further; but that is not a good way to set the timing. There are too many other factors which must be considered in choosing a timing setting. If you're going to be doing your own tuning; a timing light will be an important tool to have. With a timing light, you'll be able to see differences between the way the engine runs at different timing settings; which will not be visible or repeatable by comparing idle vacuum readings.
Ok guys, I finally found some time to pull the spark plugs on my car and it turns out they were carbon fouled pretty bad, I cleaned them with a propane torch, gapped them, and put them back in. I was able to start the car without any throttle, it ran very well for about 5 seconds then stumbled and died, I did this three times. So I took off the carburetor to see if it was flooding, and it was, about an eighth of an inch of fuel was sitting on the intake. Does it sound like my float is adjusted improperly? Is there some way to test this without taking apart the carburetor, and if the carburetor needs to be taken apart how many seals would need to be replaced?
The fact that there was fuel on the floor of the manifold after three failed cold starts does not necessarily mean the carburetor was flooding. It simply means that there was a lot of extra fuel which was not drawn into the engine. That could have come from a carb which was flooding; but it also could have come from a choke that was adjusted too rich, or from a choke vacuum break that was disconnected or had a ruptured diaphragm, or from idle mixture screws which were set too rich, or from a clogged air filter, or from a weak ignition system, or from ignition timing that was out of adjustment, or from low cylinder compression. So I hope you can see that the float is only one of many items which can cause excess fuel to build up in the manifold.
There is a simple test you can do to see whether the float chamber is overflowing: just take off the air cleaner lid, and push the choke butterfly open with a screwdriver, while the engine is idling. If the engine promptly loses speed and stalls; then the float chamber is not overflowing. If the float chamber is overflowing; the engine will run faster and smoother when you push the choke open.
Another test for an overflowing float chamber is to open the choke and look into the carb throat right after the engine stalls or is shut off. There should be no fuel dripping or pouring from the venturi nozzles after the engine stops. If fuel keeps coming out of the venturi nozzles after the engine stops; that means the float chamber is overflowing.
A flooding carb will also put a steady stream of black smoke out the exhaust, for as long as the engine runs. But some brief amounts of black smoke may be normal on many engines during cold starts; so you need to be careful about that one. In order to reliably indicate flooding; the smoke would need to continue steadily.
If a carb float chamber is overflowing; it is much more likely that it comes from a leaking float needle; rather than from a float that is out of adjustment (unless someone has been trying to set the float level). But if the car has previously been running well; and the carb has not been worked on; it is unlikely that the float adjustment has changed. The float adjustment is usually very stable.
Float needles will frequently leak if any dirt has gotten into the fuel lines. The dirt usually comes from a clogged fuel filter, or from handling the fuel lines with dirty hands during filter replacement. Many float needles have neoprene rubber tips; which can swell and deform from exposure to alcohol, or the solvent additives in modern fuels. And if the float needle tip changes shape; the needle will no longer seal against fuel pump pressure, so the carb will flood. The float level can be set perfectly in those situations, but the needle will still leak.
Some plastic floats can also be damaged by solvents and alcohol; which can lead to them soaking up gasoline, and thus becoming heavy. Hollow brass floats can fill up with gasoline through a pinhole or a crack in a solder joint, and also become heavy. When a float is too heavy; the float level may still be set properly, but the float will not sit high enough in the fuel to close the needle. Sometimes you can feel that a float is heavy when you hold it; but weighing it on an accurate scale, and comparing it to the weight to a new float is a much more reliable way of testing.
A bad choke vacuum break is almost as common a cause of flooding as an overflowing float chamber. The choke butterfly should be completely closed before the engine is cranked. If the vacuum break is working, and is properly adjusted; the choke butterfly should open slightly (1/8 to 1/4 inch) as soon as the engine starts. If the choke butterfly does not open at all when the engine starts; the vacuum break should be tested and/or adjusted.
Since it is normal for many engines to wet the floor of the manifold during cold starts; looking into the manifold is a far less meaningful test for flooding than actually looking into the carb.
And since the carb operation is dependent on manifold vacuum; the engine compression, breaker point condition and adjustment (if so equipped), ignition timing, spark plug and plug wire condition, and condition of the coil, rotor, and distributor cap must all be verified before suspecting a problem with the carburetor.
In over 30 years as a professional mechanic; I consistently found that about 85%-95% of the cars which the owner believed had a carburetor problem really had an undiagnosed ignition problem. That is a shocking statistic. I hope you all find it helpful in your own work.
The number of gaskets and seals which need replacement when a carburetor is disassembled will vary GREATLY with the brand and model of carburetor. Sometimes the float chamber cover can be removed and replaced without needing a new gasket. Other carb models seem to always need new gaskets. That's why it is so important to mention the brand and model of carburetor when seeking information. A single barrel carb is worlds different in design and complexity from a 4 barrel.
Thanks for all of the information zaken1! This is great, now first of all my choke is not hooked up, because I do not have the choke tubes, so I am ordering an electric choke. I recently noticed my secondaries vacuum is not hooked up I need to buy it also. I am guessing it may be my secondaries that are causing this problem. I will get back to you after I get the choke and secondaries hooked up. Thanks for your help, Red
I started up my car yesterday and instead of letting it go for 3-5 seconds before it died I gave it just a touch of gas to keep the rpms between 1000-750, and it ran fine, it did not die. I think it wants to idle around 500 rpms. I do have a slightly larger cam so I think the idle would have to be raised a little from the stock setting. So how would I adjust the idle? Do the idle screws adjust the opening in the choke or do they adjust the fuel mixture?
As I said before; some different models of carburetors have totally different features and adjustment procedures. Since I don't know what kind of engine or carburetor your car has; I'll just have to guess that; if your login name is the same as your car, you have a red 1979 Pontiac Phoenix. But that car was available with three different engines; a 231 cid (3.8 liter) V-6; a 305 cid (5.0 liter) V-8; or a 350 cid (5.7 liter) V-8.
The 231 and 305 engines originally used a Rochester 2 barrel carb. The 350 V-8 probably used a Rochester 4 barrel carb; but it might have a Holley or an Edelbrock on it if it was changed; or if it had a factory performance option.
For now; since you mentioned carb secondaries and a bigger cam; I'll assume the carb is a Rochester Quadrajet 4 barrel and you have the 350 engine. But please provide us with at least basic information about the parts you're dealing with, in future posts. Actually; the more complete the information is that you provide; the more satisfactory and accurate an answer we'll be able to give you.
From what you wrote; it seems that a little explanation may be useful here. But please excuse me if you already know this information. I can only go from what you write. There are FOUR butterfly valves on a Rochester Quadrajet. The primary and secondary throttle butterflys are both located along the bottom of the carb, deep inside. They are not visible from the top, unless you loook down into the carb after opening the choke (which is the smaller of the two butterflys on top of the carb) or opening the secondary air valve (which is the larger of the two butterflys on top of the carb).
There are two screws with the heads facing forward along the bottom edge of the FRONT of that carb. Those are the idle mixture screws. They do not adjust the choke or the throttle.
There are TWO idle speed screws mounted on the throttle linkage. Both of these screws are for the primary barrels, and are located on the SIDES of the carb. BUT THEY ARE NOT TO BE CONFUSED WITH THE IDLE MIXTURE SCREWS; which are not on the throttle linkage, and are on the front of the carb.
The hot idle speed screw is a horizontal screw on the throttle linkage on on the driver's side of the carb. That screw only controls the idle speed after the engine has warmed up, and the choke is open.
There is also a cold idle speed screw, on the BOTTOM edge of the throttle linkage on the PASSENGER SIDE; which is only intended for setting the idle speed when the choke is operating. It is usually necessary to hold the throttle linkage wide open in order to access and adjust the cold idle speed screw.
My blind but educated guess is that both idle speed screws are now probably set properly; and that the reason your cold idle speed is too slow is because the choke linkage has not been connected. So I would recommend not messing with those screws until you replace all the missing parts on that carb.
Some people try to use the hot idle speed screw to set the cold idle. The problem with that is it will make the engine idle too fast after it warms up; and will often lead to it dieseling when the key is shut off.
Sorry I edited my last post to put my car and carb info, I guess it didn't go through. I have a 1979 Fire Bird Trans am with the 403, it has the stock Rochester 4 barrel. I will give the cam information when I get home. Thanks for the idle mixture screws information, I will be sure to let you know how it is after the choke and secondaries are replaced.
OK, I have a Edelbrock carb #1406 that is about a year old. It is running very rich and turning my spark plugs black causing my truck to run very poorly. I dont know what to do to get it to not run rich. Please help me with any ideas. Email me directly at DIANNE82066@AOL.COM
We'd rather you came back here for a posted answer. We don't encourage private e-mail correspondence because we'd all like to share the answer. Normally I remove all posts with e-mails in them but since you're new I'll explain the rules. Stick around and maybe we can work this out for you.
If anyone has some suggestions, please post them here!
I can probably help you with this problem; but when someone brings a car to me and asks me to fix the carb; I always will first measure the resistance of the plug wires with an ohmmeter, check the ignition timing with a strobe light, and test the distributor vacuum and centrifugal advance, and the carb choke vacuum break with a hand operated vacuum pump, to make sure they all function properly. I will also inspect the exhaust system for leaks or major modifications; and check or arbitrarily replace the air and fuel filters. These preliminary tests are essential; because the fuel mixture is just as much affected by the ignition and exhaust system as it is by the carb. And if the timing is off, or there are any bad plug wires, or the vacuum advance or choke vacuum break is leaking; it will be impossible to adjust the carb properly.
So when you ask me to help with your carb; I need you to first make those same preliminary checks; otherwise we could both end up being misled and blindsided by an ignition problem, or a problem in another non-carburetor system. If you do not have the tools and test equipment I mentioned, it will be necessary to buy or borrow them. If you'd like, I can give you tips on where to find the least expensive and best value tools for this job.
I also will need to know the year, make, and model of your truck, along with the engine size; and whether it has a manual or automatic transmission. If the engine or ignition system has been modified in any way, or any recent work has been done which coincided with the onset of the richness; I need to know the full details.
I'm sorry to have to ask you to jump through all those hoops; but my 30+ years of experience as a carburetor, electrical, and diagnostic specialist have repeatedly demonstrated that trying to fix a carb without this information is like trying to install a spark plug with closed eyes. The chance of success would be about equal in both situations.
I had a feeling the wires are bad. I have a high performance carb and high performance distributor and a high performance exhaust modified. I do believe the wires are bad. Engine size is a 350, 1979 chevy pick up truck,automatic trans, electric choke, vacuum is good, We put the carb on about a year ago and its been runnin rich since installation. We just cant figure it out. The wires were new also since last year so I dont know if its just bad wires or what.
If you installed new wires last year, I doubt that they have gone bad. But I need a little more information, in order to zero in on the problem. Please answer each of the following questions:
Do you have any kind of add on ignition box on the truck; like a MSD CDI? If so, please provide details about the brand and model.
What kind of distributor do you have? Does it have both vacuum and centrifugal advance, or centrifugal only?
What is the brand, part number and gap of the spark plugs you use?
What kind of ignition coil are you using?
Are you using the stock intake manifold? If not; please provide complete details on your current manifold brand and type.
Are the EGR, evaporation cannister purge, and PCV systems still connected and operating; or have any of these systems been removed or disabled?
Please tell me how many degrees of ignition advance at idle you are using. And was that set with a strobe light, or with the engine not running?
Please tell me how you know the vacuum is good. There are two different issues about vacuum; one is whether the intake manifold vacuum is good, when measured with a vacuum gauge. The other is whether the vacuum operated controls on the engine; such as the vacuum advance on the distributor or the choke vacuum break, may be leaking. Did you mean that you have checked both of these things; or are you just saying the engine runs strong; but you have not checked the vacuum controls?
And please tell me why you think the wires may be bad.
There is a good chance that nothing is wrong with the parts on the truck; but that the carb just needs to be recalibrated to match your engine. All carbs must be calibrated to match the engine they are used on. Car manufacturers do this at the factory for every engine they sell. But manufacturers of performance carbs cannot calibrate their carbs in advance; because the settings depend on things like exhaust system, compression ratio, cam, intake manifold design, and all sorts of other items; which vary greatly from engine to engine. So, unlike installing a stock carb; which comes already calibrated for a proper match on a stock engine; performance carbs must be tuned to match the engine they are used on. Performance carbs usually come set on the rich side; so that people who do not tune them will be less likely to burn up their engines.
I'll be able to be more specific, after seeing your answers to the questions I asked.
No,ignition add on box Excel distributor and has both vacuum and centrifugal advance Just changed to Autolite spark plugs part #26 gap 45 just a cheapie ignition coil using a stock 4 barrel manifold no EGR, no evaporation cannister purge, and PCV systems IS still hooked up how many degrees of ignition advance at idle....dont remember offhand but it was set with a strobe light I have all new vacuum lines, etc...all vacuum has been checked properly
How would go about setting the carb to a specific engine?
Thank you very much for the details! Everything you have said so far sounds all right. But I have questions about the distributor and coil.
That engine originally used a HEI distributor, with the coil mounted inside the distributor cap. Accel makes high performance replacement distributors in both HEI type, with the coil in the cap, and in conventional type; which uses an external coil. Please tell me which type of distributor you have. If you have the type which uses an external coil, there could be a problem with the model of cheapie coil you are using. External coils can be bought in models with at least three different primary winding resistances: typically either 0.4 ohms; 1.3 ohms, or 3.0 ohms. If your coil is the round tin can type; chances are it has too high a resistance. And that could lead to plug fouling.
If you have the HEI type distributor, and are still using the same coil that came in the original Chevy distributor; it may have gone bad. Those GM HEI coils are known to be unreliable. So I would recommend replacing the coil in either case. If you tell me which type of distributor you have, I'll suggest a good, economically priced coil.
The way to tune a carb to a specific engine is to select a combination of metering rods, springs, and jets which will provide the proper air/fuel mixture over the entire range of speeds and loads. This would require buying an Edelbrock # 1487 calibration kit (which is made for your # 1406 carb). Summit Racing sells this kit for $37.95. But I suggest holding off a while longer before jumping into that. There are still a few things that can be done, starting with replacing the coil, which may clean up the plugs without getting into the carb.
I forgot to ask: Does this engine have a stock fuel pump; or has a high performance mechanical or electric fuel pump been installed? Some aftermarket fuel pumps produce more pressure than stock pumps. If there is a high pressure pump on your truck, it should have an adjustable fuel pressure regulator in the line from the pump to the carb; so that the fuel pressure can be set to desired levels. Otherwise, it will cause the fuel mixture to always be too rich.
The spark should be blue-white. If it is yellow or orange, that means it is weak.
There is a problem that sometimes happens when another coil is installed in a HEI distributor. The coil is held in place by sheet metal style screws at each corner, which thread into the plastic cap. But there were two different lengths of screws that were used in different brands of HEI distributor caps. Some brands of caps were designed to use the longer screw, while some were designed to use the shorter screw. If a longer screw is used in a cap that was designed for the shorter screw; the screw will go too deeply into the plastic, and will poke out through the inside surface. The exposed screw will then become a potential place where sparks from the rotor can jump, and then ground out through the coil core. And that will make the spark much weaker. That is why new caps come with new coil screws; and only those screws must be used to mount the coil; even if there are other screws that were already in the coil.
Accel wires are made in several different styles. Some have a carbon graphite resistor core; others have a spirally wound metal wire core; and others have a tinned copper core. The spirally wound metal core is the best for performance; but that type is only sold in premium priced (over $90 per set) Accel 300+ Ferro-Spiral 8.8mm race wires.
The tinned copper core is not suitable for street vehicle use; because it creates illegal levels of radio interference (and also interferes with some electronic equipment). That type of wire is only available in 7mm; which is not normally used in HEI applications.
The carbon graphite resistor core is available in both 7mm and 8mm sets; under the name Accel Super Stock. The 7mm sets cost about $24. The 8mm sets cost about $32+. This wire comes in both Universal and Custom Fit sets. The Universal sets come with plug boots and terminals pre-installed; but the distributor terminals and boots are in a separate package, and must be installed on the ends of the wire after it is cut to length. And if the wire is not stripped and terminated properly; the connections at the distributor end will have excessive resistance; which will create weak sparks. But the Custom Fit sets (which only come in 8mm) come with terminals and boots already installed at both ends.
If you have a Custom Fit set; I would not expect any problems from that wire. But if you had to install the ends on a universal set; I would check the resistance of each individual wire. The resistance should be 500 ohms per inch of wire length, when new, and can be up to 1,000 ohms per inch on used wire. Anything higher than that is excessive. And if you have a 7mm set; I would trash it; regardless of the resistance.
Summit Racing sells a blue 8mm spirally wound metal core Custom Fit set with 270 ohms per foot resistance (which is 22.5 ohms per inch), made for your truck, under part # SUM-868836, for $26.95.
Yes, I would suggest you change the coil, as well as the wires. Summit sells several different types of coils that would be appropriate. Because of the economics of purchasing in volume; their best deal is to buy a kit which contains a 50,000 volt HP coil, a HD distributor cap and HD rotor with brass terminals, a coil cover, and a wire retention ring. Their price for the complete kit is $44.95. Since the price for the coil alone is at least $31.95; while buying a cap and rotor separately costs at least $27; there is a substantial saving in buying the whole kit at once; and it also covers the possibility that your old cap may have been damaged.
The kit is available in two different colors. The red kit (# SUM-850013) costs $44.95. The kit with a blue cap, wire retention ring and rotor (# SUM-850009) costs $53.95.
I also want to point out that it is critically important to make sure the coil is properly grounded. There are three terminals in the cap for the coil primary wires. The center one is the ground terminal. If the coil comes with a seperate black ground wire, attached to a male blade connector; the connector should go in the center terminal; and the other end of the black wire should be placed under the head of one of the coil mounting bolts. If the coil only comes with the two colored primary wires; there should also be a metal ground strap; which is placed so that the male connector goes into the center terminal, and the body of the ground strap is fastened under the head of one of the coil mounting bolts.
After the ignition parts are installed, I would like to make some changes to the ignition timing. So you'll need to use a strobe timing light to do this.
:sick: I just rebuilt my edelbrock performer carb and now it continues to bog down in between 40-50 mph. I checked the float levels and double checked the measurements of 7/16 and 15/16 drop. Engine will run great at WOT but bogs down when cruising. I hooked up my vacuum gauge and it read 10 hg, I have re-adjusted the floats to 3/8 because of the engine flooding out and fuel squirting out of the top of the accelerator pump, I also have changed out the intake manifold gaskets and siliconed them into place due to the reading on the vacuum gauge. Should I adjust the float drop to somewhere around 1' to 1 1/16' to get the needle valves to close sooner. This is the second time I have posted this on the forum and Any help is appreciated. :sick:
This is also the second time I am advising you to connect the distributor vacuum advance to the manifold vacuum spigot on the carb; rather than the ported vacuum spigot. Did you ever do that?
If I give you advice, and you try it and find it didn't work, I NEED TO HEAR ABOUT THAT. The way I work is to use feedback from my suggestions to indicate what direction to take from that point; so I can zero in on an issue. But if you don't give me feedback, then we can't make any progress.
I need to know what you mean when you say the engine wouldn't hold an idle. Are you saying that it idled slower and stalled; or are you saying that the idle became too fast; or did it become unsteady and rougher? If it stalled; that sounds to me like the vacuum advance diaphragm is ruptured, and was bleeding air into the carb when you tried to run it at idle from manifold vacuum. The normal thing that happens when the vacuum advance is hooked up to manifold vacuum is that the idle speeds up. When that happens; the idle mixture and speed screws need to be readjusted.
:confuse: My main question is still, Why is there fuel squirting out of my accelerator pump?? typically that means the carb is flooding , can I increase my float drop so the needle valves will close sooner ??? The idle when hooked up to manifold vacuum sped up initially and then rpms slowly dropped and engine died.
It is normal for fuel to squirt out of the accelerator pump nozzle whenever the throttle is moved. But fuel should not come out of that nozzle while the engine idles. If you're getting a steady stream of fuel out of the accelerator pump when the throttle is not being moved, then there is a problem in the accelerator pump circuit.
Since the accelerator pump nozzle is located in the venturi, where it is exposed to high vacuum; fuel would be drawn out of that nozzle by suction; unless there was a means of blocking the fuel flow when the accelerator pump was not being driven by throttle movement. The device which is intended to prevent random fuel flow through the pump nozzle is usually a check ball which rests on top of the fuel supply passage; just underneath the pump nozzle, and/or a small weight; which is sometimes shaped like a tapered needle with the tapered end pointing downward (when there is no ball), or sometimes is just a round rod placed on top of the ball (when the rod's weight is used to hold the ball down). If that ball or weight is lost when the carb was worked on; it would cause this problem. That symptom would be similar to what happened when the carb was flooding; but the difference is that, when the carb floods; the fuel will drip out of the main discharge nozzles. If the pump check weight is missing, the fuel will come out of the pump nozzle. So fuel bleeding into the venturi is not necessarily caused by flooding!!!
Do you have a stock fuel pump on that motor? Some high performance fuel pumps produce more pressure than a stock pump. If you have a high performance pump on the motor; it may be necessary to install an adjustable fuel pressure regulator in the line between the pump and the carb; to reduce the fuel pressure to the 3 to 4.5 psi which the carb was designed to work with. A pump which produces too much fuel pressure will cause the carb to flood, when the float level is set to the normal specification.
The float drop adjustment is simply a limit stop to prevent the float from dropping too low. It is unrelated to the float level adjustment, and has no effect on the point where the needle closes. All of these adjustments are designed to work at their specified settings. Altering these settings sometimes may affect the mixture; but there will be undesired side effects of doing so. That is why messing with these settings is not the proper way to tune the carb. If the carb is flooding, or the accelerator pump is bleeding fuel; you need to find and correct whatever is directly causing that to happen, instead of changing unrelated systems. Otherwise; you add new problems to the existing problem. Carb work can be complicated enough without adding to the complexity.
There is one other major problem with this carb; which I believe is central to the issues that you have been confronting. I recognized it during the last round of exchanges you had on this site; but there was so much else going on at that time, and so many other people involved that I felt unwilling to throw more fuel on the fire:
The idle system calibrations are intended to provide the correct fuel/air mixture, under normal operating conditions. This carb is designed to be used on an engine that is equipped with a PCV system, an EGR system, and an evaporation cannister purge circuit. All three of those systems add more air to the total mixture volume. I understand that you have disabled some, or all of those systems. The consequence of doing so is that the fuel mixtures then goes way too rich; both at idle, and at cruise. And that makes it impossible to properly adjust the idle mixture, within the range of travel of the adustment screws. That is why you have to close the mixture screws so far down; but are still getting too much richness and too little total mixture volume at idle. Installing leaner metering needles will compensate to some degree; but you still have an idle circuit which is way too rich; and now have compensated by adding a mid range circuit which is way too lean (and that is what causes the mid range hesitation you are complaining about).
If the distributor vacuum advance diaphragm was ruptured; it would bleed air into the idle circuit when the distributor was connected to manifold vacuum. The increased air would act like a vacuum leak. Since the idle mixture was too rich; adding air would initially cause the engine to speed up. However, it sounds like the leak was large enough that, after the excess richness was burned off; the mixture then became too lean, and the engine slowed down and stalled. If you had opened the mixture screws a few turns at that time, the idle would probably have stabilized, and you then would have had to slow the speed down.
I write this based on the assumption that the vacuum advance diaphragm was ruptured, and was bleeding air and not advancing the timing when it was connected to a vacuum source. But the engine could also have acted similarly; if the vacuum advance was not ruptured, and increasing the spark advance was causing the mixture to lean out. That, too would eventualy cause the engine to slow down and stall.
In order to sort out this situation; you really need to get a hand operated vacuum pump and a timing light. I cannot help you further without the information those tools would provide.
The check ball and weight were properly installed and not lost during the rebuild, I have a vacuum gauge and that is where I am getting a reading of 10 Hg on my manifold vacuum port while the engine is idling. Before the PCV valve was removed and replaced with a breather cap the engine was idling rough and after removal it seems to idle better but the idle mixture screws don't effect the idle at all unless they are screwed all the way in and of course the engine will die. I have installed an adjustable fuel pressure regulator on the engine even though it is a stock fuel pump that is block mounted. It is currently set at 4.0 psi. The accelerator pump leak that I am trying to describe is not leaking from the nozzles but the rod on top of the air horn. It only leaks here when I really get on it with the accelerator.
Just went out to tinker around and when I started the engine it ran good for about one minute until the vacuum pressure slowly began to drop and then the engine died. The carb had fuel dripping and the regulator was even backed down to 3psi just to see if it would make a difference. My first order of business should probably be to get the flooding issue fixed and then go from there, correct ??? The floats are set at 7/16 and 15/16. What else could be causing it to flood and shoot fuel out of the top of the accelerator pump and carburetor ? Could the jets be to small and be causing the fuel to "back up" ??
Just went out to try and fix the flooding issue, I decided to pull the cap off of the inlet where the PCV should go. When I did this the idle evened out and the engine ran great with no flooding, I turned it off and set the timing to TDC and gave it some throttle to check and see if the advance was working and it was, what would cause these symptoms with the PCV because there is no way I can drive it with an open port on my carb. I also tried to put the PCV setup back on but it caused the engine too idle much slower and eventually die. :confuse:
Removing the cap on the PCV spigot allowed more air to get into the mixture, which leaned it out. The air that came in is comparable in volume to the air that would have come in if you had a PCV valve hooked up. And that's what I have been saying all along; that your having plugged up the PCV system is what made it run so rich, messed up the calibrations, and made it impossible to adjust the idle.
If you find that using the old PCV valve makes it idle much slower, and eventually die; this means that air is not getting through the valve and into the carb. That could come from a plugged up valve or hoses, from using the wrong type of valve, or putting the valve in backwards; or could also come from not having the top half of the PCV system in place. The top half of the PCV system consists of a vent hose from the air cleaner to one of the valve covers. This allows filtered air to get into the engine. The PCV valve, which is on the valve cover on the other side, then carries the air that came in from the air cleaner and traveled across the engine, to be drawn into the carb, and added to the air/fuel mixture. If you have an aftermarket chrome air cleaner on the Edelbrock carb; you may have to buy an elbow hose fitting (called a KV fitting) at an auto parts store and drill a hole in the air cleaner base plate to mount it. You'll also need an opening on the valve cover to mount the vent hose.
If you don't want to deal with the hassle of modifying the valve covers and the air cleaner; you can alternately just run a hose into the carb PCV spigot, and put a small filter of some sort on the end of the hose. You could adapt an air filter from a small motorbike, or a lawnmower to the hose; by using a little ingenuity. Summit Racing also sells a filtered valve cover breather that would be perfect for this application. Their part # G3417 fits into a 1 inch hole, and costs $9.95. All you'd need to do would be to adapt the hose from the carb spigot to a short length of 1 inch hose; which the breather would then plug it to.
My experience with this type of arrangement is that, after you get the timing set properly (which will require a timing light, so that you can then make small adjustments and know how much you changed it), and the vacuum advance connected to manifold vacuum, and the carb mixture and idle speed screws properly adjusted; an open hose will flow too much air and lean the mixture out excessively. So it then becomes necessary to insert a restrictor plug into the hose. Such a plug can be easily made from a 1/2 inch length of aluminum rod; of a diameter which fits snugly into the hose. Drilling a lengthwise hole of a desired diameter in the rod creates the restriction. The hole size should be at least .078" (5/64 or #47 drill bit) and might end up as large as .125" (1/8"). My guess is that it would probably work best at about .096" (#41 drill bit).
One final tip is that the test you made; of static timing the engine to TDC, and then giving the engine some throttle to see if the advance was working; could not tell the difference between advance from the centrifugal or the mechanical advance mechanism. They both advance the timing when you give the engine throttle. I also do not understand how you could conclude that the advance was working, without using a timing light.
I set the timing with a timing light, I only static timed the engine when I couldn't get it to start before I had the timing light. I will run to the auto parts store and pick up a breather filter to hook up to the PCV port after I get home from school this afternoon. When I hook up the PCV valve and hose to the correct port with a new PCV valve it won't hold an idle with or without the PCV installed in the valve cover.
The experience you've had with the PCV valve indicates that the engine is severely lacking the air it needs for proper combustion. The PCV valve adds some resistance to the hose; but the engine as it is currently set up apparently now needs all the air it can get. So it looks like you will not need to add the calibrated restriction which I previously mentioned to the hose; just run it wide open (and hope the breather filter does not make it too restrictive).
I wanted to mention that the fuel discharge you observed under heavy throttle from the float chamber vent tube may be a deliberately designed feature of this carb. Late model carbs have adopted an additional fuel enrichment system called "pull over enrichment." This is done by placing a tube so that the bottom end extends into the fuel in the float chamber, while the top end is situated in the carb throat. The diameter and location of this tube is designed so that it does not discharge fuel under normal loads; but when the throttle is opened wide, the air velocity in the carb throat reaches the point where it begins to pull fuel through the tube. And that fuel adds richness to the mixture at top end. This system enables the mid range mixture to be set lean enough for maximum economy, while still permitting the high speed mixture to be rich enough for maximum power. The dfference between a pull over enrichment nozzle and a float chamber vent tube is that a float chamber vent tube will be vertical; with the top end pointing straight up. A float chamber vent will also have an inside diameter of about 1/4" to 5/16". A pull over enrichment nozzle will be much smaller in diameter; and its discharge end will typically be horizontal or point slightly downward.
Once you get the breather hose and filter installed, I suggest you drive the truck around, so that the plugs can clean up; and then see if you can adjust the idle mixture screws to not have to be so far closed. If you still find that the mixture screws work best when they are within a half turn of being fully closed; then the idle mixture is still too rich. In that case, it may become necessary to make some changes to the idle system calibrations.
I would also like you to check the timing at idle with the vacuum advance hose disconnected; in order to get a base line reference. Then connect the vacuum advance hose to manifold vacuum, and check the timing again. Tell me the two figures you get.
I would also like to know the answer to three more questions:
1> Does this motor have a thermostat in the cooling system, and how far up does the temperature gauge run under normal driving?
2> Do you have an add on ignition control box of any kind on this vehicle; such as a MSD CDI or similar system? If so, please tell me the brand, model, and any other details about the coil type and any non stock ignition parts.
3> Please tell me the spark plug brand, part number, and gap you are using.
Temp is usually around 170, I have an Accel coil and th spark plugs are AC Delco R43S, I just installed the breather cap and hooked it up to the PCV port and the engine idled fine initially but still stuttered between 40-50 mph and ended up dying on me twice when I took a sharp turn. Removed the hose to the PCV port and ran fine to get me home but still stuttered in between the pre-stated speeds. Moved the vacuum advance to the manifold port and engine did speed up, re adjusted the idle speed to 800 rpms.
Do you know what year your engine is? AC Delco R43S plugs were only used on Chevy V-8s made before 1970. That plug has a 3/8 inch thread reach and uses a gasket. Chevy V-8s made since 1971 use a different design plug; which has a 31/64 inch (.472) thread reach, and does not have a gasket. Instead of a gasket; it has a tapered seat; which mates with the tapered seat in the head. If your engine has tapered seat heads, the plugs you are using are almost .100" too short. This will cause the plugs to carbon up, and the engine to not respond properly. The old engines also used a different plug gap that the later ones. So, before we go any further, I need to know what year your engine is.
I also am confused about the vacuum readings you report. You previously said you had set the timing so that the engine was getting 18" of vacuum at idle. Now you say it only gets 10". What brought about that change???
You also have said that turning the distributor counter clockwise retards the timing. That is not true. Turning the distributor counter clockwise advances the timing.
Were you able to open up the idle mixture screws after connecting the vacuum advance to manifold vacuum? If so; about how much did you open them?
Regarding which way to turn the distributor to advance the timing; there are two easy way to figure it out on any engine. One is to see which direction the distributor rotor turns when the starter cranks. In order to advance the timing, you turn the distributor body in the OPPOSITE direction to the direction in which the rotor turns. The Chevy V-8 distributor rotor turns clockwise; so the distributor body would need to be turned counter clockwise to advance the timing.
The second way is to look at which direction the vacuum spigot on the vacuum advance is pointing. When you apply vacuum to the vacuum advance; the vacuum pulls the distributor base plate in the direction the vacuum spigot points; so turning the distributor in that same direction will advance the timing. When standing on the passenger side of the engine; the vacuum advance on a Chevy V-8 will be on the left side of the distributor, and the vacuum spigot points toward the right. If you turn the distributor so that the vacuum advance moves toward the right, which will advance the timing; you'll be turning the distributor counter clockwise.
And when you use a timing light to look at the direction the timing marks on the crank pulley move when the engine is speeded up and the timing advances; they move to the left (counterclockwise). So if you have a timing scale with TDC in the center; the degree marks to the left of TDC will be advanced (before TDC), and the degree marks to the right of TDC will be retarded (after TDC).
Now that your vacuum advance is run from manifold vacuum; you will need to disconnect the vacuum hose before you can use a timing light to check the timing. I suggest you set the timing somewhere between 5 and 15 degrees BTDC at idle, with the vacuum advance hose disconnected. Then put the hose back on. Whenever you change the timing, recheck the idle mixture adjustment. In general, when you advance the timing; the mixture will become leaner; so the mixture screws will usually then have to be opened further.
I'm not sure as the year of the engine as I just bought the truck a few months ago and it is a chevy sbc in a 1965 Ford F-100. The only way that I can get my vacuum reading to rise above 10 Hg is to advance the timing. I was backwards on my counterclockwise statement earlier, clockwise=retarded counterclockwise=advanced.
If you can get a suffix code (numbers followed by a 2 or 3 letter code) off the ledge on the front RIGHT cylinder head, or get a casting number off the left REAR of the engine as it meets the bell housing (large series of numbers, 8 or 9), we can tell you what block you have.
The only thing I'm concerned about with reference to the engine year is whether it takes the gasket type plugs or the tapered seat "peanut plugs." Even if you found the engine year, the dude (or chick) who previously owned it may have installed different heads on it.
A more pertinent approach would be to remove the easiest to reach spark plug, and look closely at the head surface surrounding the spark plug opening. Use a screwdriver with a rag wrapped around the tip to clean away any dirt in that area. If that head takes gasket type plugs, there will be a FLAT RING surrounding the plug threads. That ring will be slightly recessed, and will have a SHOULDER on the outer edge.
If the head is designed for tapered seat plugs, there will be a tapered area around the plug threads, which blends into the head surface with no shoulder at the outer edge.
Since the plug number you gave me is also the coldest plug AC Delco makes in that thread reach, I expect the heat range (and probably the gap setting) is also a poor match for this engine. So please do not run out and buy different plugs until we get through this examination period, and I come up with a recommendation for a replacement plug type and brand.
After the right plug is in this engine, I'll help you to find the ignition timing setting which is most suitable for this motor.
There is also one more issue I feel ought to be resolved before the tuning can be properly sorted out. I need to know the specifics about the Accel coil that is on that motor. If you can find a model number on that coil, that would be great. If you cannot find a model number; then please go to www.accel-ignition.com and download their catalog from the following link: http://www.accel-ignition.com/CatalogsDownloads.aspx?brandId=3&ID=65
Once you have that catalog, please go through the coil photos CAREFULLY (since some of the coils have very small differences in appearance) and try to find the one that is on your engine. Please tell me the model number you come up with.
This coil is yellow, with a black top; is that correct?
You previously said that this car does not have points. I just want to make sure that we're both talking about the same part. Please click on the following link and look at the picture:
Is that the type of distributor cap and rotor which is on your engine? Does your distributor cap have a sliding metal window on it; like the one in the picture? Now take off the distributor cap, and look underneath the rotor; do you see a part that looks like the part pictured in the second link (below)? That is a set of breaker points for a Chevy V-8 distributor.
OK; so you have a stock distributor without points in it. In that case, there must be another device in there which takes the place of the points; to switch the coil on and off, in order to produce the sparks that ignite the fuel to keep the engine running.
And that device must be triggered by some means. It is either a Hall Effect sensor which detects the position of the 8 peaks on the distributor cam lobes; or a magnetic sensor which is activated by small magnets imbedded in a plastic wheel mounted under the rotor; or a plastic wheel with alternating narrow open slots and wide solid areas, which act as an optical shutter to alternately block and allow passage of a light beam, that triggers an optical sensor.
I would like to know what type of device is in there; so I can then determine whether the Accel coil model on that engine is an appropriate match for that particular type of ignition triggering device. Whatever it is; this device will have two or three wires coming from it. Perhaps you can find it, and see if there is a name or number on it. If it would be helpful to you, let me know and I'll post a few links to pictures of the most likely types of devices.
I'd also like to point out that it is relatively easy to notice the difference between a gasket type spark plug seat and a tapered spark plug seat in the cylinder head: Once a spark plug is out, you can reach in toward the spark plug hole with a flat bladed screwdriver. Position the blade so that it rests on an edge of the hole. From that point, hold the the screwdriver blade lightly pressed against the surface of the head, while sliding the blade in a straight line away from the plug opening; until you have moved the blade a distance equal to the diameter of the plug opening (which is 9/16" or 14mm). If the screwdriver blade does not strike a shoulder while moving that far; the head is made for tapered seat plugs. If the blade strikes a shoulder, you won't miss it; because the shoulder will be at least 1/8" high. If it strikes a shoulder; the head is the older design; intended for gasket seat plugs.
Good Morning, Crampton. Having not heard from you for a few days; I'm willing to bet that you feel this discussion has run up against a brick wall. It can be incredibly frustrating to work on some kinds of car problems; but there are qualities we all have within us which can be used to get out of those situations. One of those qualities is humility (the willingness to admit when you don't understand something). Another one is forbearance (the ability to keep going through tough situations without giving up). And the third essential quality is trust (in both the people who teach and advise you, and in the reality of your own perceptions).
Today, I'd like to get back on the progress track. This will take some humility, some forbearance, and some trust. But I promise you that if you stay with the process until you see the results; you'll love what it leads to!!!
Back in the 1960s, when Chevy V-8s all had points; a growing movement developed among young people who wanted to get beyond all the problems in our society which were caused by people's closed mindedness, intolerance and unwillingness to question traditional beliefs. This movement led to many needed changes; it brought the end to a war that had dragged on for many years, and had killed countless Americans and Vietnamese, and bitterly divided our country. It led to a fresh new wave of musical groups, like the Beatles, the Rolling Stones, the Jefferson Starship (formerly the Jefferson Airplane) and the Grateful Dead. And it produced all sorts of bumper stickers about this new way of thinking and dealing with others. My all time favorite bumper sticker from this period simply read "QUESTION AUTHORITY."
It can be tricky to question people in authority without either coming off as being disrespectful, or being a fool; but sometimes it becomes absolutely necessary. Sometimes major corporations do stupid things which cause lots of problems with their products. General Motors is on the verge of bankruptcy because of some of the stupid decisions they made. And one of the problems you are now encountering with your truck is the consequence of a stupid decision GM made in the 1960s.
This is how it happened: All cars used to have radio antennas sticking up out of their fenders or roof; but those antennas kept getting broken off by vandals, and by the brushes in motorized car washes. So GM engineers came up with a brilliant new idea; to embed the antenna wires in the front windshield. That way they would be protected from breaking. This solved the antenna breakage problem; but it had several downsides. One consequence was that if the windshield broke, and was replaced with anything other than an expensive GM windshield; the radio antenna would be gone. Another consequence was that the windshield antenna turned out to be great at picking up electromagnetic noise, which was generated by the arcing of the breaker points in the distributor. So GM then designed an electromagnetic interference shield, which was installed under the rotor in the distributor. This sheet metal shield completely surrounded the points; and served to ground off the radio waves from the points, so they could not reach the nearby windshield antenna.
But the stupid thing that GM did about that system was they failed to consider that the shield made it look like there was nothing under the rotor. As a result; when someone who was unfamiliar with this system worked on the engine, they would mistakenly conclude there were no points that needed replacing or adjustment. They could have avoided this problem if they had simply placed a label on the shield; explaining that there were servicable parts inside. But the arrogant executives at GM apparently believed everybody would know about GM designs; either that, or it would drive more owners back to the dealerships for service. Today, thirty five years after the last EMF shield was manufactured on a GM distributor; this situation is much, much worse. Most mechanics long since took the shield off and trashed it. It is not needed if there isn't an antenna in the windshield; and it gets in the way when the points are serviced. Hardly anybody remembers that EMF shield; and the typical response of a mechanic who sees the shield for the first time is that there is solid metal underneath the rotor.
But back to the way you could have helped here: You found yourself in a situation where I said something that did not match what you saw with your own eyes. I said there were either points or some other type of switching device under the rotor; but you saw what looked like solid metal under the rotor. I understand that it might be intimidating to question someone who is obviously an authority; when you see something that directly contradicts what they told you. But there is a nice way you could have done that: Suppose you just said "I looked under the rotor; and there is no room there for anything like a set of points. There is no room for anything under the rotor; it is all solid metal. What do you think is going on here?"
If you had asked me that; it would have jogged my memory, and I would have remembered the stupid EMF shield. But instead, you just said "There are no points in the distributor." That conveyed the image to me that the space under the rotor was all open and there was nothing in it. And that just didn't make sense. THERE HAS GOT TO BE A SWITCHING DEVICE IN THE DISTRIBUTOR; OR THE MOTOR COULDN'T RUN.
Fortunately, when I was reflecting on this problem, I eventually remembered the shield. But what would have happened if I had not remembered? This is the kind of situation where women have an advantage over most men. Women typically do not approach a problem from a position of pride or egoism. They are quick to admit they do not understand something; and that is what makes them much better learners. But it is tough for men to admit when they are ignorant (especially when they are dealing with an authority, or when other men are watching); and that pride all too often keeps them from accomplishing as much as they otherwise could.
I hope this helps you toward becoming more successful!!!
Nope, not frustrated. I graduate culinary school in three weeks so my wife and I took the opportunity to go visit my family out of state over the holiday and believe it or not they only have dial up internet. I am back in town and will post shortly.
Pulled the distributor and rotor, there is a set of breaker points like the picture on the website that you posted. The points on my 350 are slightly different as mine has one black wire that seems to ground out to the vacuum advance bracket and another black wire going to the Accel coil. Could breaker points that are "bad" cause the low vacuum and bogging down that I have been experiencing?
I started the engine and decided to adjust the points via the metal access panel on the distributor, but when I checked the vacuum gauge it was reading a 0hg. I checked the gauge to make sure it was working properly and it was, when throttled up it was reading around 10hg. I went ahead and adjusted the points up to the highest throttle and re-adjusted the a/f mixture screws and the idle. The bog between 40-50 mph is gone but the low end power is not what it was before. I will continue to tweak the carb and attempt to get as much as I can out of it. If you have any more advice I would love to hear it and if I need any more help I know where to g. Thanks for everything.
You can't tune the car by ear. The points have to be set a the specified gap (or dwell if you can find a dwell-tach use the window). Once you set the points, you then adjust the timing to a reasonable number (vacuum advance disconnected and plugged. Then you adjust the idle speed at the carb. Gotta get the basics right.
Comments
It may be possible to increase the vacuum by advancing the timing further; but that is not a good way to set the timing. There are too many other factors which must be considered in choosing a timing setting. If you're going to be doing your own tuning; a timing light will be an important tool to have. With a timing light, you'll be able to see differences between the way the engine runs at different timing settings; which will not be visible or repeatable by comparing idle vacuum readings.
There is a simple test you can do to see whether the float chamber is overflowing: just take off the air cleaner lid, and push the choke butterfly open with a screwdriver, while the engine is idling. If the engine promptly loses speed and stalls; then the float chamber is not overflowing. If the float chamber is overflowing; the engine will run faster and smoother when you push the choke open.
Another test for an overflowing float chamber is to open the choke and look into the carb throat right after the engine stalls or is shut off. There should be no fuel dripping or pouring from the venturi nozzles after the engine stops. If fuel keeps coming out of the venturi nozzles after the engine stops; that means the float chamber is overflowing.
A flooding carb will also put a steady stream of black smoke out the exhaust, for as long as the engine runs. But some brief amounts of black smoke may be normal on many engines during cold starts; so you need to be careful about that one. In order to reliably indicate flooding; the smoke would need to continue steadily.
If a carb float chamber is overflowing; it is much more likely that it comes from a leaking float needle; rather than from a float that is out of adjustment (unless someone has been trying to set the float level). But if the car has previously been running well; and the carb has not been worked on; it is unlikely that the float adjustment has changed. The float adjustment is usually very stable.
Float needles will frequently leak if any dirt has gotten into the fuel lines. The dirt usually comes from a clogged fuel filter, or from handling the fuel lines with dirty hands during filter replacement. Many float needles have neoprene rubber tips; which can swell and deform from exposure to alcohol, or the solvent additives in modern fuels. And if the float needle tip changes shape; the needle will no longer seal against fuel pump pressure, so the carb will flood. The float level can be set perfectly in those situations, but the needle will still leak.
Some plastic floats can also be damaged by solvents and alcohol; which can lead to them soaking up gasoline, and thus becoming heavy. Hollow brass floats can fill up with gasoline through a pinhole or a crack in a solder joint, and also become heavy. When a float is too heavy; the float level may still be set properly, but the float will not sit high enough in the fuel to close the needle. Sometimes you can feel that a float is heavy when you hold it; but weighing it on an accurate scale, and comparing it to the weight to a new float is a much more reliable way of testing.
A bad choke vacuum break is almost as common a cause of flooding as an overflowing float chamber. The choke butterfly should be completely closed before the engine is cranked. If the vacuum break is working, and is properly adjusted; the choke butterfly should open slightly (1/8 to 1/4 inch) as soon as the engine starts. If the choke butterfly does not open at all when the engine starts; the vacuum break should be tested and/or adjusted.
Since it is normal for many engines to wet the floor of the manifold during cold starts; looking into the manifold is a far less meaningful test for flooding than actually looking into the carb.
And since the carb operation is dependent on manifold vacuum; the engine compression, breaker point condition and adjustment (if so equipped), ignition timing, spark plug and plug wire condition, and condition of the coil, rotor, and distributor cap must all be verified before suspecting a problem with the carburetor.
In over 30 years as a professional mechanic; I consistently found that about 85%-95% of the cars which the owner believed had a carburetor problem really had an undiagnosed ignition problem. That is a shocking statistic. I hope you all find it helpful in your own work.
The number of gaskets and seals which need replacement when a carburetor is disassembled will vary GREATLY with the brand and model of carburetor. Sometimes the float chamber cover can be removed and replaced without needing a new gasket. Other carb models seem to always need new gaskets. That's why it is so important to mention the brand and model of carburetor when seeking information. A single barrel carb is worlds different in design and complexity from a 4 barrel.
Thanks for your help,
Red
The 231 and 305 engines originally used a Rochester 2 barrel carb. The 350 V-8 probably used a Rochester 4 barrel carb; but it might have a Holley or an Edelbrock on it if it was changed; or if it had a factory performance option.
For now; since you mentioned carb secondaries and a bigger cam; I'll assume the carb is a Rochester Quadrajet 4 barrel and you have the 350 engine. But please provide us with at least basic information about the parts you're dealing with, in future posts. Actually; the more complete the information is that you provide; the more satisfactory and accurate an answer we'll be able to give you.
From what you wrote; it seems that a little explanation may be useful here. But please excuse me if you already know this information. I can only go from what you write. There are FOUR butterfly valves on a Rochester Quadrajet. The primary and secondary throttle butterflys are both located along the bottom of the carb, deep inside. They are not visible from the top, unless you loook down into the carb after opening the choke (which is the smaller of the two butterflys on top of the carb) or opening the secondary air valve (which is the larger of the two butterflys on top of the carb).
There are two screws with the heads facing forward along the bottom edge of the FRONT of that carb. Those are the idle mixture screws. They do not adjust the choke or the throttle.
There are TWO idle speed screws mounted on the throttle linkage. Both of these screws are for the primary barrels, and are located on the SIDES of the carb. BUT THEY ARE NOT TO BE CONFUSED WITH THE IDLE MIXTURE SCREWS; which are not on the throttle linkage, and are on the front of the carb.
The hot idle speed screw is a horizontal screw on the throttle linkage on on the driver's side of the carb. That screw only controls the idle speed after the engine has warmed up, and the choke is open.
There is also a cold idle speed screw, on the BOTTOM edge of the throttle linkage on the PASSENGER SIDE; which is only intended for setting the idle speed when the choke is operating. It is usually necessary to hold the throttle linkage wide open in order to access and adjust the cold idle speed screw.
My blind but educated guess is that both idle speed screws are now probably set properly; and that the reason your cold idle speed is too slow is because the choke
linkage has not been connected. So I would recommend not messing with those screws until you replace all the missing parts on that carb.
Some people try to use the hot idle speed screw to set the cold idle. The problem with that is it will make the engine idle too fast after it warms up; and will often lead to it dieseling when the key is shut off.
If anyone has some suggestions, please post them here!
best
Shifty the Host
So when you ask me to help with your carb; I need you to first make those same preliminary checks; otherwise we could both end up being misled and blindsided by an ignition problem, or a problem in another non-carburetor system. If you do not have the tools and test equipment I mentioned, it will be necessary to buy or borrow them. If you'd like, I can give you tips on where to find the least expensive and best value tools for this job.
I also will need to know the year, make, and model of your truck, along with the engine size; and whether it has a manual or automatic transmission. If the engine or ignition system has been modified in any way, or any recent work has been done which coincided with the onset of the richness; I need to know the full details.
I'm sorry to have to ask you to jump through all those hoops; but my 30+ years of experience as a carburetor, electrical, and diagnostic specialist have repeatedly demonstrated that trying to fix a carb without this information is like trying to install a spark plug with closed eyes. The chance of success would be about equal in both situations.
Do you have any kind of add on ignition box on the truck; like a MSD CDI? If so, please provide details about the brand and model.
What kind of distributor do you have? Does it have both vacuum and centrifugal advance, or centrifugal only?
What is the brand, part number and gap of the spark plugs you use?
What kind of ignition coil are you using?
Are you using the stock intake manifold? If not; please provide complete details on your current manifold brand and type.
Are the EGR, evaporation cannister purge, and PCV systems still connected and operating; or have any of these systems been removed or disabled?
Please tell me how many degrees of ignition advance at idle you are using. And was that set with a strobe light, or with the engine not running?
Please tell me how you know the vacuum is good. There are two different issues about vacuum; one is whether the intake manifold vacuum is good, when measured with a vacuum gauge. The other is whether the vacuum operated controls on the engine; such as the vacuum advance on the distributor or the choke vacuum break, may be leaking. Did you mean that you have checked both of these things; or are you just saying the engine runs strong; but you have not checked the vacuum controls?
And please tell me why you think the wires may be bad.
There is a good chance that nothing is wrong with the parts on the truck; but that the carb just needs to be recalibrated to match your engine. All carbs must be calibrated to match the engine they are used on. Car manufacturers do this at the factory for every engine they sell. But manufacturers of performance carbs cannot calibrate their carbs in advance; because the settings depend on things like exhaust system, compression ratio, cam, intake manifold design, and all sorts of other items; which vary greatly from engine to engine. So, unlike installing a stock carb; which comes already calibrated for a proper match on a stock engine; performance carbs must be tuned to match the engine they are used on. Performance carbs usually come set on the rich side; so that people who do not tune them will be less likely to burn up their engines.
I'll be able to be more specific, after seeing your answers to the questions I asked.
Excel distributor and has both vacuum and centrifugal advance
Just changed to Autolite spark plugs part #26 gap 45
just a cheapie ignition coil
using a stock 4 barrel manifold
no EGR, no evaporation cannister purge, and PCV systems IS still hooked up
how many degrees of ignition advance at idle....dont remember offhand but it was set with a strobe light
I have all new vacuum lines, etc...all vacuum has been checked properly
How would go about setting the carb to a specific engine?
hope I didnt forget anything...
That engine originally used a HEI distributor, with the coil mounted inside the distributor cap. Accel makes high performance replacement distributors in both HEI type, with the coil in the cap, and in conventional type; which uses an external coil. Please tell me which type of distributor you have. If you have the type which uses an external coil, there could be a problem with the model of cheapie coil you are using. External coils can be bought in models with at least three different primary winding resistances: typically either 0.4 ohms; 1.3 ohms, or 3.0 ohms. If your coil is the round tin can type; chances are it has too high a resistance. And that could lead to plug fouling.
If you have the HEI type distributor, and are still using the same coil that came in the original Chevy distributor; it may have gone bad. Those GM HEI coils are known to be unreliable. So I would recommend replacing the coil in either case. If you tell me which type of distributor you have, I'll suggest a good, economically priced coil.
The way to tune a carb to a specific engine is to select a combination of metering rods, springs, and jets which will provide the proper air/fuel mixture over the entire range of speeds and loads. This would require buying an Edelbrock # 1487 calibration kit (which is made for your # 1406 carb). Summit Racing sells this kit for $37.95. But I suggest holding off a while longer before jumping into that. There are still a few things that can be done, starting with replacing the coil, which may clean up the plugs without getting into the carb.
I forgot to ask: Does this engine have a stock fuel pump; or has a high performance mechanical or electric fuel pump been installed? Some aftermarket fuel pumps produce more pressure than stock pumps. If there is a high pressure pump on your truck, it should have an adjustable fuel pressure regulator in the line from the pump to the carb; so that the fuel pressure can be set to desired levels. Otherwise, it will cause the fuel mixture to always be too rich.
I have a HEI distributor
I have a stock fuel pump that is also brand new'
What do you think of Accel wires?
There is a problem that sometimes happens when another coil is installed in a HEI distributor. The coil is held in place by sheet metal style screws at each corner, which thread into the plastic cap. But there were two different lengths of screws that were used in different brands of HEI distributor caps. Some brands of caps were designed to use the longer screw, while some were designed to use the shorter screw. If a longer screw is used in a cap that was designed for the shorter screw; the screw will go too deeply into the plastic, and will poke out through the inside surface. The exposed screw will then become a potential place where sparks from the rotor can jump, and then ground out through the coil core. And that will make the spark much weaker. That is why new caps come with new coil screws; and only those screws must be used to mount the coil; even if there are other screws that were already in the coil.
Accel wires are made in several different styles. Some have a carbon graphite resistor core; others have a spirally wound metal wire core; and others have a tinned copper core. The spirally wound metal core is the best for performance; but that type is only sold in premium priced (over $90 per set) Accel 300+ Ferro-Spiral 8.8mm race wires.
The tinned copper core is not suitable for street vehicle use; because it creates illegal levels of radio interference (and also interferes with some electronic equipment). That type of wire is only available in 7mm; which is not normally used in HEI applications.
The carbon graphite resistor core is available in both 7mm and 8mm sets; under the name Accel Super Stock. The 7mm sets cost about $24. The 8mm sets cost about $32+. This wire comes in both Universal and Custom Fit sets. The Universal sets come with plug boots and terminals pre-installed; but the distributor terminals and boots are in a separate package, and must be installed on the ends of the wire after it is cut to length. And if the wire is not stripped and terminated properly; the connections at the distributor end will have excessive resistance; which will create weak sparks. But the Custom Fit sets (which only come in 8mm) come with terminals and boots already installed at both ends.
If you have a Custom Fit set; I would not expect any problems from that wire. But if you had to install the ends on a universal set; I would check the resistance of each individual wire. The resistance should be 500 ohms per inch of wire length, when new, and can be up to 1,000 ohms per inch on used wire. Anything higher than that is excessive. And if you have a 7mm set; I would trash it; regardless of the resistance.
Summit Racing sells a blue 8mm spirally wound metal core Custom Fit set with 270 ohms per foot resistance (which is 22.5 ohms per inch), made for your truck, under part # SUM-868836, for $26.95.
Thanks SO much for all your knowledge and helping me out. I sure hope the new coil and wires does the trick.
The kit is available in two different colors. The red kit (# SUM-850013) costs $44.95. The kit with a blue cap, wire retention ring and rotor (# SUM-850009) costs $53.95.
I also want to point out that it is critically important to make sure the coil is properly grounded. There are three terminals in the cap for the coil primary wires. The center one is the ground terminal. If the coil comes with a seperate black ground wire, attached to a male blade connector; the connector should go in the center terminal; and the other end of the black wire should be placed under the head of one of the coil mounting bolts. If the coil only comes with the two colored primary wires; there should also be a metal ground strap; which is placed so that the male connector goes into the center terminal, and the body of the ground strap is fastened under the head of one of the coil mounting bolts.
After the ignition parts are installed, I would like to make some changes to the ignition timing. So you'll need to use a strobe timing light to do this.
I need to know what you mean when you say the engine wouldn't hold an idle. Are you saying that it idled slower and stalled; or are you saying that the idle became too fast; or did it become unsteady and rougher? If it stalled; that sounds to me like the vacuum advance diaphragm is ruptured, and was bleeding air into the carb when you tried to run it at idle from manifold vacuum. The normal thing that happens when the vacuum advance is hooked up to manifold vacuum is that the idle speeds up. When that happens; the idle mixture and speed screws need to be readjusted.
Since the accelerator pump nozzle is located in the venturi, where it is exposed to high vacuum; fuel would be drawn out of that nozzle by suction; unless there was a means of blocking the fuel flow when the accelerator pump was not being driven by throttle movement. The device which is intended to prevent random fuel flow through the pump nozzle is usually a check ball which rests on top of the fuel supply passage; just underneath the pump nozzle, and/or a small weight; which is sometimes shaped like a tapered needle with the tapered end pointing downward (when there is no ball), or sometimes is just a round rod placed on top of the ball (when the rod's weight is used to hold the ball down). If that ball or weight is lost when the carb was worked on; it would cause this problem. That symptom would be similar to what happened when the carb was flooding; but the difference is that, when the carb floods; the fuel will drip out of the main discharge nozzles. If the pump check weight is missing, the fuel will come out of the pump nozzle. So fuel bleeding into the venturi is not necessarily caused by flooding!!!
Do you have a stock fuel pump on that motor? Some high performance fuel pumps produce more pressure than a stock pump. If you have a high performance pump on the motor; it may be necessary to install an adjustable fuel pressure regulator in the line between the pump and the carb; to reduce the fuel pressure to the 3 to 4.5 psi which the carb was designed to work with. A pump which produces too much fuel pressure will cause the carb to flood, when the float level is set to the normal specification.
The float drop adjustment is simply a limit stop to prevent the float from dropping too low. It is unrelated to the float level adjustment, and has no effect on the point where the needle closes. All of these adjustments are designed to work at their specified settings. Altering these settings sometimes may affect the mixture; but there will be undesired side effects of doing so. That is why messing with these settings is not the proper way to tune the carb. If the carb is flooding, or the accelerator pump is bleeding fuel; you need to find and correct whatever is directly causing that to happen, instead of changing unrelated systems. Otherwise; you add new problems to the existing problem. Carb work can be complicated enough without adding to the complexity.
There is one other major problem with this carb; which I believe is central to the issues that you have been confronting. I recognized it during the last round of exchanges you had on this site; but there was so much else going on at that time, and so many other people involved that I felt unwilling to throw more fuel on the fire:
The idle system calibrations are intended to provide the correct fuel/air mixture, under normal operating conditions. This carb is designed to be used on an engine that is equipped with a PCV system, an EGR system, and an evaporation cannister purge circuit. All three of those systems add more air to the total mixture volume. I understand that you have disabled some, or all of those systems. The consequence of doing so is that the fuel mixtures then goes way too rich; both at idle, and at cruise. And that makes it impossible to properly adjust the idle mixture, within the range of travel of the adustment screws. That is why you have to close the mixture screws so far down; but are still getting too much richness and too little total mixture volume at idle. Installing leaner metering needles will compensate to some degree; but you still have an idle circuit which is way too rich; and now have compensated by adding a mid range circuit which is way too lean (and that is what causes the mid range hesitation you are complaining about).
If the distributor vacuum advance diaphragm was ruptured; it would bleed air into the idle circuit when the distributor was connected to manifold vacuum. The increased air would act like a vacuum leak. Since the idle mixture was too rich; adding air would initially cause the engine to speed up. However, it sounds like the leak was large enough that, after the excess richness was burned off; the mixture then became too lean, and the engine slowed down and stalled. If you had opened the mixture screws a few turns at that time, the idle would probably have stabilized, and you then would have had to slow the speed down.
I write this based on the assumption that the vacuum advance diaphragm was ruptured, and was bleeding air and not advancing the timing when it was connected to a vacuum source. But the engine could also have acted similarly; if the vacuum advance was not ruptured, and increasing the spark advance was causing the mixture to lean out. That, too would eventualy cause the engine to slow down and stall.
In order to sort out this situation; you really need to get a hand operated vacuum pump and a timing light. I cannot help you further without the information those tools would provide.
If you find that using the old PCV valve makes it idle much slower, and eventually die; this means that air is not getting through the valve and into the carb. That could come from a plugged up valve or hoses, from using the wrong type of valve, or putting the valve in backwards; or could also come from not having the top half of the PCV system in place. The top half of the PCV system consists of a vent hose from the air cleaner to one of the valve covers. This allows filtered air to get into the engine. The PCV valve, which is on the valve cover on the other side, then carries the air that came in from the air cleaner and traveled across the engine, to be drawn into the carb, and added to the air/fuel mixture. If you have an aftermarket chrome air cleaner on the Edelbrock carb; you may have to buy an elbow hose fitting (called a KV fitting) at an auto parts store and drill a hole in the air cleaner base plate to mount it. You'll also need an opening on the valve cover to mount the vent hose.
If you don't want to deal with the hassle of modifying the valve covers and the air cleaner; you can alternately just run a hose into the carb PCV spigot, and put a small filter of some sort on the end of the hose. You could adapt an air filter from a small motorbike, or a lawnmower to the hose; by using a little ingenuity. Summit Racing also sells a filtered valve cover breather that would be perfect for this application. Their part # G3417 fits into a 1 inch hole, and costs $9.95. All you'd need to do would be to adapt the hose from the carb spigot to a short length of 1 inch hose; which the breather would then plug it to.
My experience with this type of arrangement is that, after you get the timing set properly (which will require a timing light, so that you can then make small adjustments and know how much you changed it), and the vacuum advance connected to manifold vacuum, and the carb mixture and idle speed screws properly adjusted; an open hose will flow too much air and lean the mixture out excessively. So it then becomes necessary to insert a restrictor plug into the hose. Such a plug can be easily made from a 1/2 inch length of aluminum rod; of a diameter which fits snugly into the hose. Drilling a lengthwise hole of a desired diameter in the rod creates the restriction. The hole size should be at least .078" (5/64 or #47 drill bit) and might end up as large as .125" (1/8"). My guess is that it would probably work best at about .096" (#41 drill bit).
One final tip is that the test you made; of static timing the engine to TDC, and then giving the engine some throttle to see if the advance was working; could not tell the difference between advance from the centrifugal or the mechanical advance mechanism. They both advance the timing when you give the engine throttle. I also do not understand how you could conclude that the advance was working, without using a timing light.
I wanted to mention that the fuel discharge you observed under heavy throttle from the float chamber vent tube may be a deliberately designed feature of this carb. Late model carbs have adopted an additional fuel enrichment system called "pull over enrichment." This is done by placing a tube so that the bottom end extends into the fuel in the float chamber, while the top end is situated in the carb throat. The diameter and location of this tube is designed so that it does not discharge fuel under normal loads; but when the throttle is opened wide, the air velocity in the carb throat reaches the point where it begins to pull fuel through the tube. And that fuel adds richness to the mixture at top end. This system enables the mid range mixture to be set lean enough for maximum economy, while still permitting the high speed mixture to be rich enough for maximum power. The dfference between a pull over enrichment nozzle and a float chamber vent tube is that a float chamber vent tube will be vertical; with the top end pointing straight up. A float chamber vent will also have an inside diameter of about 1/4" to 5/16". A pull over enrichment nozzle will be much smaller in diameter; and its discharge end will typically be horizontal or point slightly downward.
Once you get the breather hose and filter installed, I suggest you drive the truck around, so that the plugs can clean up; and then see if you can adjust the idle mixture screws to not have to be so far closed. If you still find that the mixture screws work best when they are within a half turn of being fully closed; then the idle mixture is still too rich. In that case, it may become necessary to make some changes to the idle system calibrations.
I would also like you to check the timing at idle with the vacuum advance hose disconnected; in order to get a base line reference. Then connect the vacuum advance hose to manifold vacuum, and check the timing again. Tell me the two figures you get.
I would also like to know the answer to three more questions:
1> Does this motor have a thermostat in the cooling system, and how far up does the temperature gauge run under normal driving?
2> Do you have an add on ignition control box of any kind on this vehicle; such as a MSD CDI or similar system? If so, please tell me the brand, model, and any other details about the coil type and any non stock ignition parts.
3> Please tell me the spark plug brand, part number, and gap you are using.
Thank you for your cooperation!.
.
I also am confused about the vacuum readings you report. You previously said you had set the timing so that the engine was getting 18" of vacuum at idle. Now you say it only gets 10". What brought about that change???
You also have said that turning the distributor counter clockwise retards the timing. That is not true. Turning the distributor counter clockwise advances the timing.
Were you able to open up the idle mixture screws after connecting the vacuum advance to manifold vacuum? If so; about how much did you open them?
The second way is to look at which direction the vacuum spigot on the vacuum advance is pointing. When you apply vacuum to the vacuum advance; the vacuum pulls the distributor base plate in the direction the vacuum spigot points; so turning the distributor in that same direction will advance the timing. When standing on the passenger side of the engine; the vacuum advance on a Chevy V-8 will be on the left side of the distributor, and the vacuum spigot points toward the right. If you turn the distributor so that the vacuum advance moves toward the right, which will advance the timing; you'll be turning the distributor counter clockwise.
And when you use a timing light to look at the direction the timing marks on the crank pulley move when the engine is speeded up and the timing advances; they move to the left (counterclockwise). So if you have a timing scale with TDC in the center; the degree marks to the left of TDC will be advanced (before TDC), and the degree marks to the right of TDC will be retarded (after TDC).
Now that your vacuum advance is run from manifold vacuum; you will need to disconnect the vacuum hose before you can use a timing light to check the timing. I suggest you set the timing somewhere between 5 and 15 degrees BTDC at idle, with the vacuum advance hose disconnected. Then put the hose back on. Whenever you change the timing, recheck the idle mixture adjustment. In general, when you advance the timing; the mixture will become leaner; so the mixture screws will usually then have to be opened further.
A more pertinent approach would be to remove the easiest to reach spark plug, and look closely at the head surface surrounding the spark plug opening. Use a screwdriver with a rag wrapped around the tip to clean away any dirt in that area. If that head takes gasket type plugs, there will be a FLAT RING surrounding the plug threads. That ring will be slightly recessed, and will have a SHOULDER on the outer edge.
If the head is designed for tapered seat plugs, there will be a tapered area around the plug threads, which blends into the head surface with no shoulder at the outer edge.
Since the plug number you gave me is also the coldest plug AC Delco makes in that thread reach, I expect the heat range (and probably the gap setting) is also a poor match for this engine. So please do not run out and buy different plugs until we get through this examination period, and I come up with a recommendation for a replacement plug type and brand.
After the right plug is in this engine, I'll help you to find the ignition timing setting which is most suitable for this motor.
There is also one more issue I feel ought to be resolved before the tuning can be properly sorted out. I need to know the specifics about the Accel coil that is on that motor. If you can find a model number on that coil, that would be great. If you cannot find a model number; then please go to www.accel-ignition.com and download their catalog from the following link: http://www.accel-ignition.com/CatalogsDownloads.aspx?brandId=3&ID=65
Once you have that catalog, please go through the coil photos CAREFULLY (since some of the coils have very small differences in appearance) and try to find the one that is on your engine. Please tell me the model number you come up with.
You previously said that this car does not have points. I just want to make sure that we're both talking about the same part. Please click on the following link and look at the picture:
http://info.rockauto.com/Airtex/Detail.html?3D1024.jpg
Is that the type of distributor cap and rotor which is on your engine? Does your distributor cap have a sliding metal window on it; like the one in the picture? Now take off the distributor cap, and look underneath the rotor; do you see a part that looks like the part pictured in the second link (below)? That is a set of breaker points for a Chevy V-8 distributor.
http://198.208.187.182/internet/PartImage.jsp?mfgname=ACDELCO&prodlinecd=01&acpa- rtnbr=D116
Is there a part like that inside your distributor?
And that device must be triggered by some means. It is either a Hall Effect sensor which detects the position of the 8 peaks on the distributor cam lobes; or a magnetic sensor which is activated by small magnets imbedded in a plastic wheel mounted under the rotor; or a plastic wheel with alternating narrow open slots and wide solid areas, which act as an optical shutter to alternately block and allow passage of a light beam, that triggers an optical sensor.
I would like to know what type of device is in there; so I can then determine whether the Accel coil model on that engine is an appropriate match for that particular type of ignition triggering device. Whatever it is; this device will have two or three wires coming from it. Perhaps you can find it, and see if there is a name or number on it. If it would be helpful to you, let me know and I'll post a few links to pictures of the most likely types of devices.
I'd also like to point out that it is relatively easy to notice the difference between a gasket type spark plug seat and a tapered spark plug seat in the cylinder head: Once a spark plug is out, you can reach in toward the spark plug hole with a flat bladed screwdriver. Position the blade so that it rests on an edge of the hole. From that point, hold the the screwdriver blade lightly pressed against the surface of the head, while sliding the blade in a straight line away from the plug opening; until you have moved the blade a distance equal to the diameter of the plug opening (which is 9/16" or 14mm). If the screwdriver blade does not strike a shoulder while moving that far; the head is made for tapered seat plugs. If the blade strikes a shoulder, you won't miss it; because the shoulder will be at least 1/8" high. If it strikes a shoulder; the head is the older design; intended for gasket seat plugs.
Today, I'd like to get back on the progress track. This will take some humility, some forbearance, and some trust. But I promise you that if you stay with the process until you see the results; you'll love what it leads to!!!
Back in the 1960s, when Chevy V-8s all had points; a growing movement developed among young people who wanted to get beyond all the problems in our society which were caused by people's closed mindedness, intolerance and unwillingness to question traditional beliefs. This movement led to many needed changes; it brought the end to a war that had dragged on for many years, and had killed countless Americans and Vietnamese, and bitterly divided our country. It led to a fresh new wave of musical groups, like the Beatles, the Rolling Stones, the Jefferson Starship (formerly the Jefferson Airplane) and the Grateful Dead. And it produced all sorts of bumper stickers about this new way of thinking and dealing with others. My all time favorite bumper sticker from this period simply read "QUESTION AUTHORITY."
It can be tricky to question people in authority without either coming off as being disrespectful, or being a fool; but sometimes it becomes absolutely necessary. Sometimes major corporations do stupid things which cause lots of problems with their products. General Motors is on the verge of bankruptcy because of some of the stupid decisions they made. And one of the problems you are now encountering with your truck is the consequence of a stupid decision GM made in the 1960s.
This is how it happened: All cars used to have radio antennas sticking up out of their fenders or roof; but those antennas kept getting broken off by vandals, and by the brushes in motorized car washes. So GM engineers came up with a brilliant new idea; to embed the antenna wires in the front windshield. That way they would be protected from breaking. This solved the antenna breakage problem; but it had several downsides. One consequence was that if the windshield broke, and was replaced with anything other than an expensive GM windshield; the radio antenna would be gone. Another consequence was that the windshield antenna turned out to be great at picking up electromagnetic noise, which was generated by the arcing of the breaker points in the distributor. So GM then designed an electromagnetic interference shield, which was installed under the rotor in the distributor. This sheet metal shield completely surrounded the points; and served to ground off the radio waves from the points, so they could not reach the nearby windshield antenna.
But the stupid thing that GM did about that system was they failed to consider that the shield made it look like there was nothing under the rotor. As a result; when someone who was unfamiliar with this system worked on the engine, they would mistakenly conclude there were no points that needed replacing or adjustment. They could have avoided this problem if they had simply placed a label on the shield; explaining that there were servicable parts inside. But the arrogant executives at GM apparently believed everybody would know about GM designs; either that, or it would drive more owners back to the dealerships for service. Today, thirty five years after the last EMF shield was manufactured on a GM distributor; this situation is much, much worse. Most mechanics long since took the shield off and trashed it. It is not needed if there isn't an antenna in the windshield; and it gets in the way when the points are serviced. Hardly anybody remembers that EMF shield; and the typical response of a mechanic who sees the shield for the first time is that there is solid metal underneath the rotor.
But back to the way you could have helped here: You found yourself in a situation where I said something that did not match what you saw with your own eyes. I said there were either points or some other type of switching device under the rotor; but you saw what looked like solid metal under the rotor. I understand that it might be intimidating to question someone who is obviously an authority; when you see something that directly contradicts what they told you. But there is a nice way you could have done that: Suppose you just said "I looked under the rotor; and there is no room there for anything like a set of points. There is no room for anything under the rotor; it is all solid metal. What do you think is going on here?"
If you had asked me that; it would have jogged my memory, and I would have remembered the stupid EMF shield. But instead, you just said "There are no points in the distributor." That conveyed the image to me that the space under the rotor was all open and there was nothing in it. And that just didn't make sense. THERE HAS GOT TO BE A SWITCHING DEVICE IN THE DISTRIBUTOR; OR THE MOTOR COULDN'T RUN.
Fortunately, when I was reflecting on this problem, I eventually remembered the shield. But what would have happened if I had not remembered? This is the kind of situation where women have an advantage over most men. Women typically do not approach a problem from a position of pride or egoism. They are quick to admit they do not understand something; and that is what makes them much better learners. But it is tough for men to admit when they are ignorant (especially when they are dealing with an authority, or when other men are watching); and that pride all too often keeps them from accomplishing as much as they otherwise could.
I hope this helps you toward becoming more successful!!!
Joel