The carb you are talking is the ford autolite I think and if I understand what you are saying then it is your float causing the problem. I have seem this before where the float level rises higher than it should and the fuel comes out the front pole. I think the float must be adjusted by bending the float arm to the proper position.
You are correct sugar will not harm the metal parts of a car with the exception of gumming up the working of the values and pistons rings. This all happens after the car has been started and warmed up to running temperature where the sugar desolves and when engine then cools down with the sugar now turned to a glue like material that will stick the values to the point of bending instead dislarging from the value seats. it's not a wifes tale, and if you think so then try putting a cup in your tank and lets just see how much of a wifes tale it really is.
I've always been under the impression that sugar is not harmful, because as I recollect, it doesn't dissolve in the gas tank at all---well, hardly at all.
I, too, was raised with this tale of the dreaded sugar, but over time I've come to disbelieve it, especially when I put some sugar into a test container with gasoline. Give that a try (be careful!).
Well, sugar may or may not be harmful; but mothballs definitely are a different kettle of fish. I remember a story from high school when some disgruntled students poured a generous quantity of mothballs into the fuel tank of an unpopular teacher's car. When she drove down the street; it was reported that she couldn't keep the vehicle speed under control; so she pulled into a gas station and shut the engine off. They say the engine then froze up solid, and never ran again.
Here is a brief background on my set up and condition: 1979 Trans am 403 new performance headers, exhaust, slightly larger cam, with auto transmission which has sat for 10 years Freshly (less than 1k miles) rebuilt engine and transmission 10 years ago The car has all emissions removed, no cats, gas fume canisters, etc. Oil changed fuel changed transmission fluid changed
It had a leaking Holley carburetor, which was replaced with a rebuild Rochester Quadrajet (the carburetor originally on the car) the car ran fine with this Rebuilt carburetor, shortly after until I noticed the rebuilt carburetor was leaking fuel at the top of the accelerator pump, so I sent the carburetor back and put on a new non-leaking carburetor which they replaced the leaky one with (a whole different carburetor, not the last one repaired). Now I have a problem with this new carburetor, it floods the car! Currently the choke is not hooked up, however on the last carburetor the choke was not hooked up either and the car still ran and was not flooded. I thought it may have been the idle screws and they were screwed out; Left: 4.5 turns Right: 6 turns, which I then screwed them in all the way and out 2.5 turns (which is the correct starting amount before fine tuning, correct?). So what could be some of my possible issues, I imagine it is the carburetor considering the last carburetor ran fine with the car in the same state it is now. Sorry it is so long, just making sure you have the whole story. Thanks, Red
The fuel leaking at the top of the accelerator pump in the previous carburetor was most likely a sign that the float bowl was overflowing. This would be either caused by a float needle that was not shutting off the incoming fuel (usually because there is dirt caught in the needle), or by a float that had become heavy from absorbing fuel, or by a float level that had been set too high. Even though the replacement carburetor you now have does not give the same symptom; it sounds like it is suffering from the same problem: fuel level in the bowl too high.
Improper float level adjustment is so common on rebuilt carburetors that I refuse to install one without first removing the float chamber cover and checking the float level. This operation seems to be something that the rebuilders don't bother to do.
Besides that; I would consider it vitally important to install a new fuel filter in whatever carburetor you are using. On Holley installations; there is usually an inline filter somewhere in the fuel line. On the quadrajets; there is a paper filter inside the fuel inlet nut. It is essential that there either be an NEW inline filter in the line; or a NEW paper element inside the fuel inlet nut. If there is also an old inline filter in that car; I would definitely replace it. Ten years worth of rotting fuel will put lots of potential contaminants into a fuel filter. And those particles will quickly mess up the float needle on every replacement carb you install.
Regarding the choke; there is a choke vacuum break diaphragm mounted on the carb; which is designed to pull the choke butterfly open when the engine begins to run. Even if you don't have the choke linkage hooked up; the weight of the butterfly may cause it to close. If the hose to the vacuum break is not hooked up, or the vacuum break diaphragm is ruptured; the choke butterfly probably will not be pulled to a vertical position when the engine is warmed up, and that can cause flooding. But when the mixture is set right; it normally will be necessary for the choke to close in order for the engine to start. (But when the float bowl is overflowing, the engine will start easily with no choke. That is a bad sign; it means it is flooding.)
2 1/2 turns on the idle mixture screws should be OK for a baseline setting. That is not the source of your problem.
If the float needle is not seating properly you'll get a steady drip drip drip into the manifold even as the car just sits. This would mean you're flooded even before you attempt to start the car.
Try starting with the gas pedal to the floor and just KEEP IT THERE and don't pump it except the one time to floor it--if it starts after a while then you are flooding overnight as there was no other way for the gas to get in there.
Oh another related common Rochester Q=jet problem is that the "main well plugs" leak and allow the fuel bowl to empty overnight. They are supposed to be sealed with lead at the time of the rebuild but some rebuilders are careless. You can seal them with quick-set epoxy.
FLOAT LEVEL -- also very critical on a Q-jet. The float level is measured from the rear of the float to the top of the float bowl casting. Also if your float seems "heavy" that means it is porous and will therefore drop down and float the engine.
If you remain frustrated, get a rebuild from RaceKrafters in Lancaster PA. The BEST IN THE WORLD. 717-399-8780
First of all I forgot that it has a high performance Holley fuel pump which I believe is capable of pumping nine times the necessary fuel, with this in mind I put a fuel pressure gauge on the line which read only 2 psi (it is possible the reading was incorrect due to a faulty gauge). That seems low to me I thought the recommended pressure was 7 psi, correct me if I am wrong. To check the float would I have to replace a gasket? I have one filter which was cleaned which is before the fuel pump, on inline after the fuel pump (brand new), and the paper one on the rebuilt carburetor is brand new also. So I am doubtful that it is a filter, although the fuel has a yellow hue which I believe is from rust in the gas tank. For the choke, I had the choke butterfly open and tried to start the car, then I made sure the choke was closed and tried to start the car with no success so I believe the choke is ruled out. I can get the car to run if I give it gas and keep giving it gas while it is running, it will not idle. Thank you for your help zaken1 I'm looking forward to your response! Red
I’m not sure if it is a steady drip drip, but before I tried to start the car I removed the carburetor to make sure the manifold was dry, I will try to start the car tomorrow at WOT I think it will start at WOT. To check the main well plugs I could take off the carburetor in the morning (with a full bowl) and put it on top of a bucket to test that. As for float level like I asked zaken1 in the previous post, can I inspect the float without needing to replace a gasket, and how difficult is it to get to it.
On a side note one other test I ran for the possible of fuel pressure being to high was I took the carburetor off, put it on a bucket and just ran the fuel pump for about a minute with no leaks, so maybe my fuel pressure can be disregarded for now, and by the way it does not have a regulator or return.
I checked my manifold to see if it had any gas in it today and the passenger side had a little gas and the driver’s side was dry, I then put back on the carburetor and tried flooring it to start it and it wouldn't start. After that I removed the vacuum advance vacuum, I am not sure if I should have but this is what I heard I should do while I am just trying to get the car running. I then tried to get it to start with out pressing the gas peddle, it started for a few moments but it was stumbling, I then went to WOT and it wouldn't start again, tried to start it without giving it gas and it wouldn't start, so I opened the throttle and looked down in the manifold it had about an eighth of an inch of gas. What position should the choke be in when the car is starting and when the car was just started?
Since the car wouldn't start when you floored it, but started when you didn't give it any throttle; it sounds like the car was starved for fuel (at least at that particular moment).
It should not be necessary to disconnect the hose for the vacuum advance when trying to start the engine. The only reason that would be necessary would be if you intend to check or reset the ignition timing as soon as it begins running. But if you don't need to mess with the timing; it probably will run better if the vacuum advance is left connected.
The choke should be fully closed before you try to start the engine. The choke vacuum break will probably pull the choke butterfly about 1/4 inch open at the center of the top edge while the engine is cranking. And it should stay open about that much when the engine first runs. During the first 5 minutes of running, the choke should gradually open further; until it is fully vertical by the time the temperature gauge begins to rise.
If you shut the engine off when the engine has not warmed up, the choke should close completely again, but you'll probably have to step on the throttle slightly, in order to allow the choke to move to that position. If you shut the engine off when it is fully warmed up; the choke should stay open until the engine cools off. Again, the fast idle cam may keep the choke butterfly from resetting, until you briefly step on the throttle.
If you find that the engine continues to stumble after it starts; it would be a good idea to pull the spark plugs, and see if any of them have become carbon fouled. A wet or carbon fouled plug will not run reliably. So you may need to clean or replace the plugs, in order for the engine to run right. A propane torch or a glass bead blaster is the only way to clean plugs. The purpose of plug cleaning is to have the black and wet deposits removed from the porcelain insulator. The condition of the metal plug electrodes is not important in the cleaning; as long as nothing is bridging the gap.
The plugs are fairly new I replaced them a few months ago, but I imagine your right and it is possible they are fouled because of the flooding. So I will pull the plugs as soon as I get a chance and get back to you. Thanks -Red
:confuse: I just rebuilt my edelbrock performer carb and now it continues to bogdown 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. The manual says to measure the outer end of the float. Does that mean the end away from the pin or the end with the pin that holds the float???Any help isappreciated.
The outer end of the float is the end away from the pin. It is important that both pontoons be at the same height.
There is also a metering rod adjustment; which is at least as critical in its effect on performance. It sounds to me like the metering rods are not adjusted right. It also may be possible to install stronger metering rod springs; which would effectively richen the mixture.
Those rods are also available in many different diameters. If you have made other changes to the motor; such as the exhaust system, ignition, or camshaft; the metering rods which you previously used may no longer be suitable. Selecting new rods or springs may involve some experimentation. These rods have two or three different steps in diameter. The smallest diameter step is for the top end mixture; the next larger diameter is for cruise and mid range; and the largest diameter step (if there is a third step) would be for the lower portion of the cruise and mid range. Larger diameter steps will run leaner, and smaller diameter steps will run richer. Since you say the top end performance is now good; if you decide to try different rods, I would recommend using rods which have the same or very similar diameter small end; with a smaller diameter mid range step. These rods and springs are available from Edelbrock, and from speed shops. Jeg's and Summit Racing are likely to have them.
It is also possible to tune the mid range mixture by installing an adjustable fuel pressure regulator, and finding the pressure setting which gives the best mid range and cruise performance. I would recommend using a continuously adjustable regulator; rather than the cheaper kind that adjust in half pound increments. Holley makes one of the best value regulators. They have a street regulator for carbureted applications which is made in a low pressure (1-4psi) and a higher pressure (4.5-9psi) model. Summit sells them for $27.95. Summit also sells their own adjustable regulator; which is identical to the Holley high pressure model, for $24.95.
Another item that can cause bogging at cruise is a disconnected or defective distributor vacuum advance unit (assuming there is one on your distributor). So it should be checked to see if it receives vacuum, and that the diaphragm is not ruptured (if the diaphragm is bad; it will not hold vacuum and not advance the timing when vacuum is applied to it) There are usually two different types of vacuum ports on carbs. One is called ported vacuum; that type of source does not supply vacuum at idle, but begins to have vacuum when the throttle is opened. The other type is called manifold vacuum; that type has strong vacuum at idle, and also has strong vacuum when the throttle is opened. Many engines will pull stronger and get better mileage when the vacuum advance is driven by manifold vacuum; regardless of what the source was originally. But when you change from ported to manifold vacuum; the idle speed may increase enough that it has to be slowed down.
I have changed out the return springs on the metering rods with an assortment kit that I bought. The vacuum advance is on the port vacuum and is working fine. I had a major issue with the carb flooding after the rebuild, could the for mentioned symptoms be caused by fouled plugs??? No vacuum leaks, new plugs and wires (about 2 months old), floats adjusted properly(7/16 with a 15/16 drop) , fuel pressure is at 5 1/2 psi, truck idle is set at 850 rpms at idle and 650 rpms when in gear, adjusting a/f screws out doesn't seem to effect the rpm's unless they are screwed in almost all of the way and it chokes the engine out. Just wanted to let you know some more information so you can better understand what is going on. Thanks for your help.
If the plugs were fouled; I would expect it to have a far greater effect on full throttle operation than on the cruise and mid range. Since you report that the top end performance is good; I wouldn't suspect fouled plugs.
But the mid range and cruise bogging may well be caused by too rich a fuel mixture. If the metering rod springs you're using are too strong; it would cause an excessively rich mixture during cruise. This would load up (partly foul) the plugs during mid range driving; so they would not respond well at part throttle. But when you floored it; if the mixture is correct at wide open throttle, the plugs would clean up and the engine would then run well, until you returned to part throttle cruise.
So I would suggest trying a weaker set of metering rod springs; or metering rods with a larger diameter mid range step. If there is an adjustment on the upper stop for the metering rods, you could also set it so the rods can not lift up so far.
However, if you have changed to a colder plug heat range, or are using too small a plug gap, or are using a CDI with a plug gap smaller than .045"; this would also cause the bogging you reported.
To find the diameter of your metering rods; you would need to take one out of the carb, and measure it with a micrometer or dial caliper. Edelbrock has a chart of available rod diameters for their various carb models.
If your fuel pressure now is 5 1/2psi, a fuel pressure regulator could make a significant difference. I would say you could drop the pressure to as low as 3 1/2 psi. But the difference would not be as great as installing metering rods which were .004" larger on the mid range step. An increase of .004" on a metering rod would be a pretty big change. I would consider that much of a change only appropriate in a situation where the engine was obviously running too rich.
You could pull and inspect the spark plugs, after driving a few miles at between 40 and 50mph. If the plugs had black porcelains and black deposits on the shell and ground electrodes; that would indicate excess richness. But if the plugs came out with tan or white insulators; that would mean it is not too rich. If the ground electrodes and plug shells were tan or light gray, while the porcelain was black; the plug's heat range is too cold.
And I would recommend changing the vacuum advance source to manifold vacuum; and then (after the motor is fully warmed up, and has been driven a few miles) readjusting the idle speed to normal and then turning the mixture screws in just to the point where the engine begins to lose smoothness. You might find that the performance improves enough that it won't be necessary to change the metering rods.
I have a mechanic friend that thinks I have a vacuum leak. He said to check the intake gasket, is this a god place to start looking ??? Could I possibly have a vacuum leak from the power booster since it is the only other vacuum besides the advance timing ???? I changed out the metering rods with a calibration kit from edelbrock and it didn't seem to help. Thank you for your help.
If there was a vacuum leak in the power brake booster; it usually would result in either the brakes feeling a lot weaker than they used to; or the idle becoming rougher whenever you stepped on the brake pedal. If you don't have either of those symptoms; I doubt there is a vacuum leak in the power brake system.
If this is a Chevy or GMC truck, and it has an automatic transmission; there also is a vacuum tee in the intake manifold behind the carb; that connects to a line which supplies vacuum to the transmission modulator. Sometimes that line will come loose; or the modulator will be defective. This usually will also lead to the transmission not shifting normally.
A vacuum leak could come from the intake manifold, or the carburetor mounting flange. One way to test for this is to squirt some oil from a pump oil can along the edges of the manifold and carburetor flanges while the engine is idling. If there is a leak, the idle quality will change when you apply oil to the leaking spot; and you'll probably see smoke start to come out of the exhaust pipe.
But any kind of a vacuum leak will usually make the idle rough, will often produce an audible hissing noise, and will typically make the engine not slow down right away when you let off the throttle. If you don't have any of those symptoms; you probably don't have a vacuum leak.
If your engine has an EGR valve; you might try temporarily disconnecting and plugging the vacuum hose to that valve. That would richen up the mid range mixture. Sometimes performance carbs don't work well with EGR valves.
But I'm still not sure whether the bogging is caused by too lean a mixture; or too rich a mixture. That would be very important to know; because it would rule out half of the possibilities. It would also indicate in which direction the mixture would need to be moved, in order to stop the bogging.
If the bogging is being caused by too rich a mid range mixture, and the metering rods you tried were richer than the ones that were previously in the carb; they certainly would not help this problem. They might even make it worse. But that doesn't mean that installing a leaner set than the original ones would not help.
That's why I asked you to run the truck a few miles at the speed where it bogs; and then pull a few spark plugs and tell me the color of the porcelain insulator and the metal shell and electrodes. The appearance of the plugs, plus knowing the engine model and plug brand and number, probably would give me an idea of whether the mixture is too lean or too rich.
The engine is an old chevy 350 that has the headers mounted above the spark plugs (horrible design), I will drive the truck later on today and pull some plugs and post my results. If there was a vacuum leak at the intake manifold would it effect the idle before the engine got up to operating temperature or just after when it would be "sucking" warm air ? I don't have any issues with my brakes directly effecting the drivability , so I will cross that off the list. Thanks again for your help.
I just replaced the metering rods with the six different sets that came in the calibration kit. Of course the last pair (0.75"x0.47) seemed to alleviate the problem of "bogging", but now I can't seem to get my idle set. And now when I turn the engine off it putters a couple of times and shuts down. According to the calibration chart in my manual I am running 1 stage rich in cruise and 2 stages rich in power, should I change my primary jets? I have also seemed to aquire the symptom of "engine stall" on some turns, engine flooding??
Just replaced primary jets with .104 jets, engine will die out after running for a few seconds, fuel squirting out top of accelerator pump, re-checked floats and measurements are right on, black smoke out of exhaust. Getting ready to re-install old jets and continue mixing springs & rods. Will pull plugs in a few minutes and list results.
Plugs are ACDelco R43S, I got the flooding issue taken care of I was off on the float drop by 1/8" on the left float. I still can't get the engine to remain running on it own under a load. Back to the plugs, pulled the #1 plug and it is completely black from carbon. Changed the jets to a .101 the originals that I pulled were .100. Could the carbon on the plugs be causing a "misfire" and be the reason for the engine not idling under load ? Thanks again !! :sick: :confuse:
Sure. What you may want to do is this. Run the car down the highway and then as you're coming home to the driveway or parking space, cut the ignition and throw it in neutral and coast to a stop, and then "read" the plugs and see how they look. If they look clean, llight brownish/tan, then your mix is probably okay.
Have you ever done a vacuum gauge check on this engine, or a compression test?
Got a a vacuum gauge, it reads at 10Hg during idle and drops to 5Hg under full throttle and when the accelerator is let off it goes up to 20-25Hg. According to the link you sent me this could mean a slight intake leak or late valve timing?
Yep, intake leak sounds plausible with that reading, so spray some carb cleaner around the intake manifold and see if the idle changes. They say to use "starter fluid" but I don't think that's a good idea--that stuff is highly explosive. Carb cleaner is safer. This presumes you don't have a freshly painted engine?
As for "late valve timing" the only thing I could think of is a very worn timing chain or worn camshaft. 10 hg is rather low vacuum.
The only thing that has changed on the engine since the carb rebuild is that I did away with the PCV and put a breather in the valve cover. If I pull the plug off of the PCV port on the carb I gain as much as 500 rpm's at idle. If I retard the ignition by spinning the distributor counter-clockwise I will also gain rpms but the engine will eventually die out. When retard the vacuum is around 14-16Hg. I have sprayed carb-cleaner and starting fluid on the intake manifold and the fan just seems to blow it off before it has a chance to make a difference. The only gasket that I can see on the intake manifold is a silicone gasket, from my experience this can wear over the long run, am I correct ? Apparently I need to pull the intake and check the gasket, how big of a task is this on a SBC 350. It looks like all I need to do is pull the thermostat housing, carb, distributor and ignition coil to access all of the bolts, am I correct. Once again thank you !
One way is you use one of those hand vacuum pumps that you hook up to the vacuum advance port on the distributor, squeeze the handle (engine stopped, distributor cap off) and the points should rotate. Another way is to use your timing light and watch to see the timing change at high, stable rpm when you connect and disconnect the vacuum hose to the distributor.
:mad: I just changed my intake manifold gasket and engine wouldn't start after. It did backfire thru the exhaust and carb, carb was on fire when I got to the hood. What the F*#! ??? Doused it with water, thats all I had available. :mad:
Just tried starting the engine and it wouldn't turn over almost like it is locked up, pulled the distributor and moved a couple of teeth with the same result. All I get is an electrical buzz. Is my timing off ??
I have the #1 cylinder at TDC, and set the oil pump screw at an angle from 12:30-6:30 and cannot get the distributor to drop the last 1/4". The oil pump seems to have a "wiggle" in it, so when I touch the distributor to it it will wiggle out of the way and the distributor will not slide into place. Is there any way to tighten the oil pump screw so it doesn't wiggle around ??
Why don't you static time it just to get into the ballpark. Bring the #1 cylinder to TDC on the compression stroke (you can do this by cranking with a remote starter and keeping your finger over the hole---when compression pushes your finger out, that means you are on the compression stroke not the exhaust stroke.
Then hand turn the engine until you are at TDC on the pulley.
Then hook up a test light to the + wire on the distributor (the one that connects to the coil)---one clip to the + terminal on the distributor, the other to ground.
Then, turn the ignition key to ON. Your test light might be on or off, doesn't matter. Rotate the distributor in the direction of the rotor until it goes out. Then rotate it COUNTER to the rotor until it JUST goes on.
Then clamp down the distibutor and you are static timed and good enough for the engine to run well.
Got the engine running didn't have a test light so I used an electrical multimeter and adjusted according to the 12V reading, thanks for the help on the timing. Still only reading 10Hg on the vacuum gauge when hooked up to the manifold vacuum port on the carb, any ideas. I sprayed the intake with carb cleaner to see if there was a leak and the idle never changed. I waited until after I got the timing set to check the oil level (like an idiot) and there was water in it from the carb fire. Drain and fill with oil ? Any additives to the engine to help protect it from the water ? THANKS AGAIN TO EVERY ONE FOR THE TIMING HELP
Changed the oil twice, first one ran for 30 min with sea-foam to help take care of th water. Still only read 10Hg on the vacuum gauge when hooked up to the manifold vacuum port. Engine was static timed so I advanced the distributor until vacuum read 18Hg. Engine is purring like a kitten, thanks again to all. What is the vacuum pressure supposed to be, might as well get it right on the money.
Comments
Anyway, here's one opinion on the subject.
Sugar's Not The Way To Attack Your Enemy
I, too, was raised with this tale of the dreaded sugar, but over time I've come to disbelieve it, especially when I put some sugar into a test container with gasoline. Give that a try (be careful!).
1979 Trans am 403 new performance headers, exhaust, slightly larger cam, with auto transmission which has sat for 10 years
Freshly (less than 1k miles) rebuilt engine and transmission 10 years ago
The car has all emissions removed, no cats, gas fume canisters, etc.
Oil changed fuel changed transmission fluid changed
It had a leaking Holley carburetor, which was replaced with a rebuild Rochester Quadrajet (the carburetor originally on the car) the car ran fine with this Rebuilt carburetor, shortly after until I noticed the rebuilt carburetor was leaking fuel at the top of the accelerator pump, so I sent the carburetor back and put on a new non-leaking carburetor which they replaced the leaky one with (a whole different carburetor, not the last one repaired). Now I have a problem with this new carburetor, it floods the car! Currently the choke is not hooked up, however on the last carburetor the choke was not hooked up either and the car still ran and was not flooded. I thought it may have been the idle screws and they were screwed out; Left: 4.5 turns Right: 6 turns, which I then screwed them in all the way and out 2.5 turns (which is the correct starting amount before fine tuning, correct?). So what could be some of my possible issues, I imagine it is the carburetor considering the last carburetor ran fine with the car in the same state it is now.
Sorry it is so long, just making sure you have the whole story.
Thanks,
Red
Improper float level adjustment is so common on rebuilt carburetors that I refuse to install one without first removing the float chamber cover and checking the float level. This operation seems to be something that the rebuilders don't bother to do.
Besides that; I would consider it vitally important to install a new fuel filter in whatever carburetor you are using. On Holley installations; there is usually an inline filter somewhere in the fuel line. On the quadrajets; there is a paper filter inside the fuel inlet nut. It is essential that there either be an NEW inline filter in the line; or a NEW paper element inside the fuel inlet nut. If there is also an old inline filter in that car; I would definitely replace it. Ten years worth of rotting fuel will put lots of potential contaminants into a fuel filter. And those particles will quickly mess up the float needle on every replacement carb you install.
Regarding the choke; there is a choke vacuum break diaphragm mounted on the carb; which is designed to pull the choke butterfly open when the engine begins to run. Even if you don't have the choke linkage hooked up; the weight of the butterfly may cause it to close. If the hose to the vacuum break is not hooked up, or the vacuum break diaphragm is ruptured; the choke butterfly probably will not be pulled to a vertical position when the engine is warmed up, and that can cause flooding. But when the mixture is set right; it normally will be necessary for the choke to close in order for the engine to start. (But when the float bowl is overflowing, the engine will start easily with no choke. That is a bad sign; it means it is flooding.)
2 1/2 turns on the idle mixture screws should be OK for a baseline setting. That is not the source of your problem.
Try starting with the gas pedal to the floor and just KEEP IT THERE and don't pump it except the one time to floor it--if it starts after a while then you are flooding overnight as there was no other way for the gas to get in there.
Oh another related common Rochester Q=jet problem is that the "main well plugs" leak and allow the fuel bowl to empty overnight. They are supposed to be sealed with lead at the time of the rebuild but some rebuilders are careless. You can seal them with quick-set epoxy.
FLOAT LEVEL -- also very critical on a Q-jet. The float level is measured from the rear of the float to the top of the float bowl casting. Also if your float seems "heavy" that means it is porous and will therefore drop down and float the engine.
If you remain frustrated, get a rebuild from RaceKrafters in Lancaster PA. The BEST IN THE WORLD. 717-399-8780
Thank you for your help zaken1
I'm looking forward to your response!
Red
On a side note one other test I ran for the possible of fuel pressure being to high was I took the carburetor off, put it on a bucket and just ran the fuel pump for about a minute with no leaks, so maybe my fuel pressure can be disregarded for now, and by the way it does not have a regulator or return.
Thanks for your help guys!
Red
What position should the choke be in when the car is starting and when the car was just started?
It should not be necessary to disconnect the hose for the vacuum advance when trying to start the engine. The only reason that would be necessary would be if you intend to check or reset the ignition timing as soon as it begins running. But if you don't need to mess with the timing; it probably will run better if the vacuum advance is left connected.
The choke should be fully closed before you try to start the engine. The choke vacuum break will probably pull the choke butterfly about 1/4 inch open at the center of the top edge while the engine is cranking. And it should stay open about that much when the engine first runs. During the first 5 minutes of running, the choke should gradually open further; until it is fully vertical by the time the temperature gauge begins to rise.
If you shut the engine off when the engine has not warmed up, the choke should close completely again, but you'll probably have to step on the throttle slightly, in order to allow the choke to move to that position. If you shut the engine off when it is fully warmed up; the choke should stay open until the engine cools off. Again, the fast idle cam may keep the choke butterfly from resetting, until you briefly step on the throttle.
If you find that the engine continues to stumble after it starts; it would be a good idea to pull the spark plugs, and see if any of them have become carbon fouled. A wet or carbon fouled plug will not run reliably. So you may need to clean or replace the plugs, in order for the engine to run right. A propane torch or a glass bead blaster is the only way to clean plugs. The purpose of plug cleaning is to have the black and wet deposits removed from the porcelain insulator. The condition of the metal plug electrodes is not important in the cleaning; as long as nothing is bridging the gap.
Thanks
-Red
There is also a metering rod adjustment; which is at least as critical in its effect on performance. It sounds to me like the metering rods are not adjusted right. It also may be possible to install stronger metering rod springs; which would effectively richen the mixture.
Those rods are also available in many different diameters. If you have made other changes to the motor; such as the exhaust system, ignition, or camshaft; the metering rods which you previously used may no longer be suitable. Selecting new rods or springs may involve some experimentation. These rods have two or three different steps in diameter. The smallest diameter step is for the top end mixture; the next larger diameter is for cruise and mid range; and the largest diameter step (if there is a third step) would be for the lower portion of the cruise and mid range. Larger diameter steps will run leaner, and smaller diameter steps will run richer. Since you say the top end performance is now good; if you decide to try different rods, I would recommend using rods which have the same or very similar diameter small end; with a smaller diameter mid range step. These rods and springs are available from Edelbrock, and from speed shops. Jeg's and Summit Racing are likely to have them.
It is also possible to tune the mid range mixture by installing an adjustable fuel pressure regulator, and finding the pressure setting which gives the best mid range and cruise performance. I would recommend using a continuously adjustable regulator; rather than the cheaper kind that adjust in half pound increments. Holley makes one of the best value regulators. They have a street regulator for carbureted applications which is made in a low pressure (1-4psi) and a higher pressure (4.5-9psi) model. Summit sells them for $27.95. Summit also sells their own adjustable regulator; which is identical to the Holley high pressure model, for $24.95.
Another item that can cause bogging at cruise is a disconnected or defective distributor vacuum advance unit (assuming there is one on your distributor). So it should be checked to see if it receives vacuum, and that the diaphragm is not ruptured (if the diaphragm is bad; it will not hold vacuum and not advance the timing when vacuum is applied to it) There are usually two different types of vacuum ports on carbs. One is called ported vacuum; that type of source does not supply vacuum at idle, but begins to have vacuum when the throttle is opened. The other type is called manifold vacuum; that type has strong vacuum at idle, and also has strong vacuum when the throttle is opened. Many engines will pull stronger and get better mileage when the vacuum advance is driven by manifold vacuum; regardless of what the source was originally. But when you change from ported to manifold vacuum; the idle speed may increase enough that it has to be slowed down.
But the mid range and cruise bogging may well be caused by too rich a fuel mixture. If the metering rod springs you're using are too strong; it would cause an excessively rich mixture during cruise. This would load up (partly foul) the plugs during mid range driving; so they would not respond well at part throttle. But when you floored it; if the mixture is correct at wide open throttle, the plugs would clean up and the engine would then run well, until you returned to part throttle cruise.
So I would suggest trying a weaker set of metering rod springs; or metering rods with a larger diameter mid range step. If there is an adjustment on the upper stop for the metering rods, you could also set it so the rods can not lift up so far.
However, if you have changed to a colder plug heat range, or are using too small a plug gap, or are using a CDI with a plug gap smaller than .045"; this would also cause the bogging you reported.
If your fuel pressure now is 5 1/2psi, a fuel pressure regulator could make a significant difference. I would say you could drop the pressure to as low as 3 1/2 psi. But the difference would not be as great as installing metering rods which were .004" larger on the mid range step. An increase of .004" on a metering rod would be a pretty big change. I would consider that much of a change only appropriate in a situation where the engine was obviously running too rich.
You could pull and inspect the spark plugs, after driving a few miles at between 40 and 50mph. If the plugs had black porcelains and black deposits on the shell and ground electrodes; that would indicate excess richness. But if the plugs came out with tan or white insulators; that would mean it is not too rich. If the ground electrodes and plug shells were tan or light gray, while the porcelain was black; the plug's heat range is too cold.
And I would recommend changing the vacuum advance source to manifold vacuum; and then (after the motor is fully warmed up, and has been driven a few miles) readjusting the idle speed to normal and then turning the mixture screws in just to the point where the engine begins to lose smoothness. You might find that the performance improves enough that it won't be necessary to change the metering rods.
If this is a Chevy or GMC truck, and it has an automatic transmission; there also is a vacuum tee in the intake manifold behind the carb; that connects to a line which supplies vacuum to the transmission modulator. Sometimes that line will come loose; or the modulator will be defective. This usually will also lead to the transmission not shifting normally.
A vacuum leak could come from the intake manifold, or the carburetor mounting flange. One way to test for this is to squirt some oil from a pump oil can along the edges of the manifold and carburetor flanges while the engine is idling. If there is a leak, the idle quality will change when you apply oil to the leaking spot; and you'll probably see smoke start to come out of the exhaust pipe.
But any kind of a vacuum leak will usually make the idle rough, will often produce an audible hissing noise, and will typically make the engine not slow down right away when you let off the throttle. If you don't have any of those symptoms; you probably don't have a vacuum leak.
If your engine has an EGR valve; you might try temporarily disconnecting and plugging the vacuum hose to that valve. That would richen up the mid range mixture. Sometimes performance carbs don't work well with EGR valves.
But I'm still not sure whether the bogging is caused by too lean a mixture; or too rich a mixture. That would be very important to know; because it would rule out half of the possibilities. It would also indicate in which direction the mixture would need to be moved, in order to stop the bogging.
If the bogging is being caused by too rich a mid range mixture, and the metering rods you tried were richer than the ones that were previously in the carb; they certainly would not help this problem. They might even make it worse. But that doesn't mean that installing a leaner set than the original ones would not help.
That's why I asked you to run the truck a few miles at the speed where it bogs; and then pull a few spark plugs and tell me the color of the porcelain insulator and the metal shell and electrodes. The appearance of the plugs, plus knowing the engine model and plug brand and number, probably would give me an idea of whether the mixture is too lean or too rich.
My usual suspects on a carburetted car when it bogs down are:
vacuum advance
accelerator pump
metering rods
Engine "run-on" could be a flooding condition (post-nasal drip, sort of) or a timing problem---your timing is too far advanced.
Have you ever done a vacuum gauge check on this engine, or a compression test?
USING A VACUUM GAUGE
As for "late valve timing" the only thing I could think of is a very worn timing chain or worn camshaft. 10 hg is rather low vacuum.
That's odd that you gain RPMs while retarding the timing. Are you sure you got that right?
Then hand turn the engine until you are at TDC on the pulley.
Then hook up a test light to the + wire on the distributor (the one that connects to the coil)---one clip to the + terminal on the distributor, the other to ground.
Then, turn the ignition key to ON. Your test light might be on or off, doesn't matter. Rotate the distributor in the direction of the rotor until it goes out. Then rotate it COUNTER to the rotor until it JUST goes on.
Then clamp down the distibutor and you are static timed and good enough for the engine to run well.