Carburetor Problems On Older Cars

andre1969

"Variable Venturi" too, in relation to Dearborn products of the late 70's/early 80's, and usually not in a good light.

I don't really know what it is, either. I did find this pic, though... dunno if it's accurate or helps much, though.

I think the butterfly valves mainly control the amount of airflow, while this variable venturi thing might be further inside, and help restrict the flow after the fuel and air has been mixed, in an attempt for better fuel economy? For instance, at low speeds/low load situations, maybe it tightens up in an attempt to reduce the flow of the mixed fuel and air, and then opens up when you stomp the gas?

fintail

I'm sure glad my fintail is FI...

alfonzottown

I remember those ...
They used them on late 1970's Fords in place of a 4 bbl
If I remember correctly they stopped the varable venturi because the ball thingy that was used in place of the lower butterfly valve had a tendency to lock up or wear out quickly.
But (in thoery) it was basically a sound idea (in thoery).

vettman2

I just inherited a 1964 Buick Lesabre 300 ci. 4bbl Rochester Carb # 7024044. Car had Carb re-built in June of 05 and set in garage until April 06. Car has manual choke, it starts on first turn with full choke, when you put in gear to drive [non-permissible content removed] you accelarate is spits & sputters and then takes off and cruises great, untill you stop and go to take off again it spits!! If you keep full choke on it will take off with less hesitation, and when you shut it off it is dieseling and you must shut off in low to prevent. Could power piston be wrong one?

Mr_Shiftright

could be all gummed up from sitting 10 months or crappy gas. One should always use a fuel stabilizer for longterm storage and I prefer to run the carb dry.

isellhondas

That Buick didn't come with a manual choke!

geo9

VETTE.....Did someone modify the choke to a manual
one?

One problem with any duojet or quadrajet carb from
long term non usage is internal leakage.
Beneath the primary venturi cluster there will be a
"T" that is inserted into the bowl floor that holds
down a ball and spring. Where this ball sits rust
or crud will form underneath the ball and cause
flooding/hot start problems.

One way to check is to shut the car off hot and look
for "smoke" coming up thru the carb "throats".
This is raw fuel leaking internally into the hot
engine and vaporizing (spl) thus the smoke !

Shifty is right about OLD gas.......I use the
Sta-bil brand fuel treatment in my summer only vehicles,
lawnmowers, generators etc.............

Mr_Shiftright

If I were him, before I took apart the QJ I'd take a gas sample and see what you're pouring in there.

vettman2

Thanks for the quick response! I tracked down the original owner of the Buick and he said they not only modified the choke, but they put an electric fuel pump on and never checked to see how much pressure it was pumping!!! I found an NOS original manual pump and I am going to install it and then I will search for a carb with the correct choke. We ran out all the old gas and have put in new fuel and the carb is a Rochester not a Carter. The owner said that my late relative whom I got the car from had the carb re-built but never checked the fuel pump situation. I have not noticed any smoke emitting from the carb after hot shut off, and we sprayed choke cleaner around the outside while running to see if any leakage and there was no change in idle when we did that. I will put mech. pump on and go from there.
Thanks again!
Vettman2

geo9

YEOW! A electric pump and running a old Q-Jet?????
Prob. pumping so much pressure its flooding that old
"nailhead" motor right out!
Its not smoking out the tailpipe(s) is it?

If not it could be as simple a bad accelerator (spl)pump......

Mr_Shiftright

Electric pump isn't a bad idea but you need to have an adjustable fuel pressure regulator in line with it or the electric pump may overpower the float valve.

vettman2

Thanks! I think the power piston is ok, but the elec. pump is more of the problem. I am going to put the right pump on and see if that helps. I talked to my nephew and he said the car ran fine untill Gramps removed the mech. pump and messed with the electric pump! I will let you know of the results.
I have never owned a "Non" sm. block Chevy, and this is all so much different. You can just about interchange anything on a Sm. Block!!!
Vettman2

dan70

I recently got a Mazda B2000. It was running well until a couple of weeks ago when I began having to goose the gas pedal to keep it on during cold-starts. Now, I have to goose the pedal to get moving, otherwise it stalls. It also feels like the carb is flooding because the truck chokes up on the road at all speeds, even when the truck is idle. I did a routine tune up -- oil change, new plugs, new filter -- but it didn't fix the problem. Do you think I need to replace the carburetor? Or could the choke just need some adjustment?

simonscharger

Hello
I own a 1974 Chevy Nova 4 Door Custom 350 with a 670cfm Holley Street Avenger, Edelbrock Performer Intake, MSD Chevy Pro-Billet Distributor (I do Not Have The Vacuum Advance Hook Up), MSD Blaster 2 Ignition Coil & MSD 8mm spark wires. Witch I use as a daily driver.

A few weeks ago I install a new fuel pump. Just a stock one from auto zone and I put a new carb on it. Before I had a holley street proformance carb that thing always gave problems. So I replace it with the street Avenger. But before I replace the carb it ran fine but when I stop Lightly or Hard it wants to stall or it just stalls out. So I thought it was the carb. So I wasn't worried about it, then I replace the carb & it still does it. So I ask the techs at my work and they told me its a vacuum leak or the power brake booster gone bad. I know it cant be a vacuum line leaking because I just replace all of them, & I did replace the brake booster, I had to replace anyways it wasn't working right. But when I replace the Booster it still does the same crap. The thing that sucks is that is I tried to get some the techs to take a look at it but they don't want to touch it because its a old car. Hope someone can help me with this problem. :sick:

mikef9

Hi,

I've got an '89 Corolla and am having some trouble cold starting recently. The electric choke, the top butterfly valve, is stuck open all the time. It never closes when the engine is running or not, hot, cold, etc. Also I can't move the valve manually, which I expect is normal. The problems starting the engine began a month or so ago.

If anyone can offer some advice, it will be much appreciated.

Thanks

burdawg

To close the valve manually, you most likely need to open the throttle a little. Try it.
It's probably a bi-metallic electrically heated spring inside the choke housing. It could have broken from age/use.

mikef9

Thanks for your reply. The problem is that I can't move the valve at all. The shaft is locked in place in the choke housing (that is the electrical box?). Is it possible to open the housing and fix?

burdawg

Possibly. Are there any screws or other fasteners holding the cover on?

mikef9

The valve won't budge at all, regardless of the throttle. The housing is closed with rivets, could probably drill those through.

thunderbird4

I have a 65 T-Bird with the Motorcraft 4100 carb. When the car is driven, it sucks the primary bowls dry. Most of the time you can run it at idle and even rev the engine in park, and the bowl replenishes.

I have changed the fuel pump, rebuilt the carb, checked the fuel pump output volume, checked for junk in the fuel lines, replaced the fuel pump flter, checked the vent in gas cap. There is absolutely no dirt in the fuel to the carb.

I have run out of things to try. I kind of feel like it's something in the carb. that I didn't fix on the rebuild.

ANY suggestions are apprecieated.

Mr_Shiftright

Seems like it has to be a sticking float valve, doesn't it?

thunderbird4

Thanks, that was one of the things I thought too....

But when I have the airhorn off, I just can't see that the floats could be sticking on the sides of the bowls, and there doesn't appear to be anyplace for them to catch on the bottom of the airhorn either.....

thunderbird4

Oops,,,, I misread,,,, you said float valve. The kit had a new inlet seat and needle (?)..... I checked and they don't appear to be sticky or gummy where they seat......

thunderbird4

I forgot to give another clue on my last post about the t-bird dieing under load.

When the airhorn is off and the gas is entering the bowl through the inlet valve, it seems to sputter quite a bit.

I thought that might have been caused by a leak on the intake side of the fuel pump, so I replaced all of the small sections of rubber fuel line that connect the metal fuel line around the bends between the fuel tank and the fuel pump.

I found no brittleness on the old pieces, and changing them didn't solve the problem......

Mr_Shiftright

Well if in fact you idle the car, and it dies, and you take the top of the carb off and there's no fuel in the float bowl, it HAS to be the float valve or you have an intermittent fuel pump. It's no different than you toilet filling up after you flush. If you had no water in the tank after the flush, what would you conclude? Either water source or float valve.

Question is...are you SURE the float bowl is empty?

reallandyacht

just a blind thought ...
Some carbs have a filter in the carb body (looks like an aquarium filter made in metel) besides the inline filter ...

this sounds like a problem I had (way back when) on a 4 bolt 327 .... it looked clean but wasn't.

Mr_Shiftright

good thought but then the fuel bowl wouldn't keep filling up sometimes---filters are either clogged or not I think, but float valves can stick/unstick as they wish.

guest

Thanks again for your reply.

Sorry, I must not have been clear. It does not die when it is in park and idles. Likewise, it does not die when it is in park and I rev it up to make it draw more gas from the bowl. The fuel level stays up with the demand completely. It only seems to run the bowl dry when it is actually being driven, even when I only drive it slowly through the neighborhood.

Yes, I am sure it is dry, because when I test drive it, I take gas with me and when it dies, I take the top off the carburetor and try to limp home on one bowl full.

I would have thought the fuel pump too, but I replaced it with no improvement. I even thought that maybe the fuel pump was drawing air on the suction side and therefore both gas and air were entering the bowl, displacing the normal volumn of gas (the gas does "spit" some as it comes out over the top of the needle). I replaced all of the rubber hose sections on the suction side of the fuel pump all the way back to the fuel tank.

The last time I drove it, I probably drove several miles in the neighborhood and it ran perfectly. When I pulled into the driveway it died. Obviously the bowl replenished itself many times on that drive and everything worked as it should.

It behaves as if for some reason that the fuel pump just shuts down during the normal operating cycle, and when the bowl drains, the fuel pump just doesn't start up again.

The only way I can start it the is to fill the bowl up manuallly, and then it keeps pumping for awhile.

I am at the end of the line on trying things. I hate to buy a new carb and I am hesitant to have this one rebuilt, since if it's not something obvious, whoever rebuilds it will miss whatever it is too..... But I guess the only way to rule out the carb is to bite the bullet and try another one.

guest

Thanks, The fuel filter on this one is a part of the fuel pump. It has what looks like a small oil filer on the bottom of the fuel filter, and the filter is inside. I looked at the old one. It looked clean, but I put in a new one anyhow..... No luck......

Mr_Shiftright

It's got to be the float valve...when you drive you consume more gas of course...so a partially stuck valve would maintain idle but not slow driving.

the only other thing I can think of, which I saw ONLY ONCE on a car, was a piece of debris, kind of flat, that would periodically lodge against the small screen just at the gas line inlet into the carburator.

guest

Thanks,,,,, I can't figure out why it would stick though. I replaced the inlet valve and needle when I kitted the carb. It didn't fix the problem.

I even removed the small filter screens below the inlet valve, just in case it was restricting the flow.

I even removed the float damper springs since they do place a slight downward pressure on the needle.

I guess I have to decide weather to buy a rebuilt carb or have mine rebuilt with new floats (just in case). I hate to lose my carb since it is the original and is date stamped on the bottom of the casting.

thunderbird4

Now that I have given up on fixing the carb problem with my T-Bird, I have decided on a "new" carburetor. What are your opinions on having one professionally kitted, or buy a "new" one?

Some of the rebuilders claim that their process and slight modifications make the carburetor perform better than new.

Mr_Shiftright

I think I'd buy a new one. You can keep the old original of course. I bet the new ones also have design improvements.

tigerman67

In general, I think you want to keep you original carb, as it adds value to the car to a true collector. Make sure the carb is cleaned out well so nothing gets cruddy on the inside before storing, if you aren't going to use it on the car right now.

I would warn you that if you buy a 'rebuilt' carb from one of the major parts stores, odds are you will not get exactly what you were looking for. For instance, the common 60's Ford carbs that I am familiar with are the 4100 and 4300. And I can walk down and buy one off the shelf at a bigger parts store. Trouble is, there were various sizes of those carbs, that can only be confirmed by looking at casting marks on carb itself. I personally needed one for a small block, and the ones they always stocked were the ones for the big blocks. If I put one of those on my small block, I would introduce a whole new set of problems because of overcarburetion.

In the case of the 4300 carb, they had a couple of nifty features including a screw in the back that I think was some form of airbleed to set the idle. It also had a funky little bimetal device on top by the secondaries, that off hand I don't remember what it does. If you buy a rebuilt, they will strip all that stuff off and those holes will simply be plugged. I assume that when they were originally built, they had a purpose and don't appreciate them simplifing the carb for me.

I happened to have bought a Sunbeam Tiger that had a Pony Carbs fully refurbished Ford 4100 carb on it, it was simply a thing of Beauty, it was fully replated, had all the correct inspection stamps and everything. The previous owner bought it (and paid a small fortune for it). He claims to have asked to have the carb set up for high altitude, but had signficant problems with it when it first arrived. He was very dissapointed in the customer service level he got from them.

Having a perfectly period correct carb on your car is nice for the car shows, but can sometimes get tough to get parts for them. If you like playing with your carb alot having a modern carb that you can go to any speed shop and get parts off the wall has alot going for it.

I don't believe there has been much new technology in carburation in the last 30 years. When ford had fully switched over to FI, I heard they sold thier patents for carburation to Holley. I believe thier patents were for side annular discharge, or some name like that which was the basic technology they had used for a very long time.

nategoff

Fuel is spitting out of the fuel pump on my 1971 Lincoln Mark III. The motor seems to be getting plenty of fuel. It runs fine. I can see the fuel spitting intermittently out of a small hole on the side of the fuel pump. What gives? How do I fix it?

Mr_Shiftright

bad diaphragm in pump. Replace it or get a rebuild kit for it. Better yet, "gut" the old pump, leave it bolted where it is, and run a hidden electric pump and fuel pressure regulator instead. Car then looks stock but runs better.

nategoff

Good advice. Thanks. Out of curiousity, why is that small hole there anyway? Pressure relief or something?

Mr_Shiftright

uh-oh...you're testing my automotive physics on arcane forms of fuel pumps...which is rusty (me, not the pumps)...I THINK the little hole is there to vent air from the diaphragm's pumping action...so really there should be no fuel on the vent side of the pump...and the only way fuel gets up there (or down there) is leaking through a split diaphragm.

moe145

There are three things (and three things only) that are required for an engine (provided it's set up internally and timed right) to start. 1) Spark. This is easy to check. Disconnect the spark plug wire and hold it near the block (with an insulated glove or rubber tongs or something insulated). It should spark to the block if it's getting spark. or you could hold it in your hand while someone cranks the motor (not recommended!!) But you will know if you have spark!. 2) Fuel. This is also very easy to check. Look in the carb and see if the fuel is spraying. Easy. Yes or no? 3) (Usually the problem) Engine timing. Have your buddy crank the motor while you use the timing light on the timing index mark. Move the distributor until it lines up the index marks near the idle setting for your engine and the motor should start when you get close. That's it. Unless your timing chain slipped a tooth or your internal engine timing is off, you will have an engine that will start. Moe out

stella61

This 7 seater mpv is not a bad car, but I am having a problem with the carburetor, what is causing the trouble is the hole where a pin has to go, that was broken so we have made do with a screw, about the same size, but it still causing problems, the car cuts out when driving along, this happens every now and again, I have tried to get a replacement pin, but I have found it impossible, have you any ideas or help on the matter, also I have read some where that one of the Nissan cars its either the Sunny or Cherry parts can be used on the Nissan prairie SLX please can you let me know if this is correct

drgadedipe

does any one have a step by stay way of converting any carburettor to any fuel injector. pls reply as soon as possible
thanks

texases

Try Googling 'fuel injection conversion' There are too many variables for a simple answer.

drgadedipe

thanks alot. it came up with alot of information. more replies are welcome

0patience

There are a ton of kits available to convert to fuel injection, but they aren't cheap.
Holley, Edelbrock and Weiand all have kits to convert to fuel injection.

It would help to know what engine you are working with.

animaljim

Your diaphram is leaking. Best to replace pump. It may also be leaking into crankcase.

alex_123

my baby, is having some major issues... hopefully someone can help..

when it sits for a day, it drives wonderful.. once its going, about ten min. or so.. it starts to put and then back fires the farther i drive. its been completely rebuilt. every last piece on it is only a few months old. the entire thing only has about 2000 or so miles on it..
i cant get it to pass emmisions either. my last VW did the same thing, and i ended up selling it. it passes wonderfully on 3 of the four, but at idle the hydrocarbons are 1028 when it should be 500. im hopeing something came lose, and from driving with that problem so long its causing it to get worse. dual carbs, and for some reason its much slower than you would expect. it drives like a normal bug. any advice whould be soo greatly appreciated.. i love this car to death. and without it passing emmisons, ive only got 3 days before my last pass expires. then ill have to tow it everywhere and have no car.. :[

thank you for your help!!!

if you live in az, and some what near gilbert, and can help me out, im a licenced hair dresser and am more than willing to trade hair for car work if its something i cant do myself...

thank you once agian!

alex

burdawg

Hard to say without more info. What kind of carbs? Were they jetted correctly for the engine? Your emissions test results lead me to believe that your running rich at idle, which means the idle mixture adjustment is way off, or the jets are way off. If you have Weber carbs ( a popular set up), then you should follow Webers' procedure to determine if the jets are set wrong for your engine. This is done by setting the idle mixture screws to a known starting point then counting the turns to get to the best idle, and changing the jets based on these results.
Also, dual carbs need to be balanced properly, which can be done by using a carb balancer, a tool that fits over the throat of the carb and meters the airflow.
Your poor performance after 10 minutes or so leads me to believe that perhaps the choke isn't adjusted properly and isn't releasing all the way. Could also be caused by running very rich though.
Anyone else have any ideas, chime in. Sorry I don't live near Gilbert. I wasn't aware that you needed to get emissions tests in Gilbert.

Mr_Shiftright

I'd say you are running too rich...with a cold engine, it likes that but when hot it doesn't like to be either "choked" or flooded with gas.

As for emissions, one always has to first off adjust the valves on a VW, especially #3 cylinder.

Dual carbs on a VW isn't a great idea to begin with. That little engine doesn't need that much carburation. If this is a normal "bug" engine and not a pancake engine, I'd go back to a single carb and manifold. If it's a pancake engine that normally runs 2 carbs, I'd check choke operation on both of them, also check valve adjustment. You could pull a spark plug and "read" how it looks....flakey dry carbon suggests way too rich a mixture....nice light brown "toast" color means okay, very light/white deposits with little pimples on it, too lean.

71chevyc10

I GOT THIS FRIEND THAT HAS A 64 CHEVY WAGON. IT BOGS DOWN BAD AT CRUISIN SPEED AND EVEN AT TIME A GOING ABOUT 20MPH. WHAT COULD POSSIBLY BE THE PROBLEM. HE HAS heI AND HOT PLUGS, ROCHESTER SINLGE BARREL V6 INLINE OF COURSE. AND IT HAS GOOD PICK UP AND IT FEELS PRETTY STRONG. BUT IT STARTS TO CHOKE AND IT BOGS DOWN AND IT FEELS LIKE ITS SUCKING AIR AND THERE IS NO GO JUST HISSING SOUNDS LIKE A SUCKING SOUND. ???? :confuse: :confuse:

Mr_Shiftright

Sounds like a large vacuum leak. He should test by squirting some carb cleaner along the base of the carburator and along the base of the intake manifold (NOT the exhaust manifold!!). Also if he has a power brake, the hose that connect the manifold to the brake booster. If he has a vacuum leak, the engine will immediately pick up speed as he squirts and the leak "inhales" the somewhat combustible carb cleaner.