Carburetor leakage!
Thread Starter
Pro
Joined: Jul 2002
Posts: 589
Likes: 8
From: Palm Bay FL
Re: Carburetor leakage! (burners)
Holley rebuild kits are cheap and easy to install. $20 or $30, you will also want a gallon of carb cleaner so you can soak it. We can walk you through this one pretty easy. In fact, you can probably figure this out easily yourself.
Le Mans Master
Joined: Aug 2000
Posts: 6,362
Likes: 7
From: Brazos TX
Cruise-In IV Veteran
Cruise-In V Veteran
Re: Carburetor leakage! (mpro72vette)
No problem. To get the correct kit for your carb you will need the numbers off of the air horn. There are several numbers stamped on it. The "list" number should be 0-6239-1.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Carburetor leakage! (mpro72vette)
Guys -
If a Holley carb has fuel puddling on the intake manifold, it is almost always from fuel dripping out of the throttle shafts after engine shutdown. This fuel comes from fuel being discharged out of the main discharge nozzle after engine shutdown: the fuel dribbles out the discharge nozzles, hits the throttle blades, and leaks right out the sides of the throttle shafts and onto the intake manifold.
Cause for this is one of the following:
1. Leaking needle/seat (replace needle/seat or rebuild carb)
2. Float level too high (adjust float levels with engine hot and running)
3. Fuel boiling in float bowl after shutdown (not much you can do about the new fuels with ethanol additives - the fuel has a lower boiling point than the old fuels)
4. Ruptured power valve (replace PV or rebuild carb)
5. Bad o-ring on accel pump transfer tube (rebuild carb)
The metering block gaskets very seldom just start leaking - these are really fail-proof connections. Once in a while you'll get an accelerator pump gasket leak, but this is also rare. I'd start with doing a hot float level setup. After shutdown on a hot engine, remove the air cleaner and take a look down the venturi and see if you can see fuel percolating out of the main discharge nozzles. If you can, you hae one of the other problems noted above.
If a Holley carb has fuel puddling on the intake manifold, it is almost always from fuel dripping out of the throttle shafts after engine shutdown. This fuel comes from fuel being discharged out of the main discharge nozzle after engine shutdown: the fuel dribbles out the discharge nozzles, hits the throttle blades, and leaks right out the sides of the throttle shafts and onto the intake manifold.
Cause for this is one of the following:
1. Leaking needle/seat (replace needle/seat or rebuild carb)
2. Float level too high (adjust float levels with engine hot and running)
3. Fuel boiling in float bowl after shutdown (not much you can do about the new fuels with ethanol additives - the fuel has a lower boiling point than the old fuels)
4. Ruptured power valve (replace PV or rebuild carb)
5. Bad o-ring on accel pump transfer tube (rebuild carb)
The metering block gaskets very seldom just start leaking - these are really fail-proof connections. Once in a while you'll get an accelerator pump gasket leak, but this is also rare. I'd start with doing a hot float level setup. After shutdown on a hot engine, remove the air cleaner and take a look down the venturi and see if you can see fuel percolating out of the main discharge nozzles. If you can, you hae one of the other problems noted above.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Carburetor leakage! (daily_driver)
Daily -
It was a good assumption on your part, though, that the carb in question was a Q-Jet, since almost all the '72s were Q-Jet cars. The LT was the exception.
Q-Jet cars can also have very similar problems with fuel puddling on the manifold. I noted that a few of you suggested that the plugs in the carb would be at fault with this symptom. Actually, when Q-Jet plugs leak, fuel tends to drip right down into the inside of the intake manifold, and the fuel does not leak out onto the outside of the manifold. I have found the leaky plug problem to be grossly over-rated, as very few Q-Jets really have leaking plugs.
If a Q-Jet is leaking fuel out onto the outside of the manifold on either side of the carb, it is usually due to fuel dribbling out the main discharge nozzles after engine shutdown, splashing onto the throttle plates, and siphoning out the throttle shafts. Like on the Holley, this is usually due to poor float level fuel control from a leaky needle/seat; a sticky needle or hung up float; excessively high float level; a fuel saturated float; or fuel boiling in the float bowl.
Also of note on the Q-Jets: Every so often I see people with problems with fuel leaking out of the upper (air horn) gasket, thinking that the gasket just needs to be changed. On a correctly set up Q-Jet, the upper gasket should never be soaked with fuel, and fuel should never touch the gasket except due to occasional fuel sloshing from cornering/acceleration/braking. If fuel is soaking the upper gasket with the vehicle at rest, there is a fuel level control problem.
It was a good assumption on your part, though, that the carb in question was a Q-Jet, since almost all the '72s were Q-Jet cars. The LT was the exception.
Q-Jet cars can also have very similar problems with fuel puddling on the manifold. I noted that a few of you suggested that the plugs in the carb would be at fault with this symptom. Actually, when Q-Jet plugs leak, fuel tends to drip right down into the inside of the intake manifold, and the fuel does not leak out onto the outside of the manifold. I have found the leaky plug problem to be grossly over-rated, as very few Q-Jets really have leaking plugs.
If a Q-Jet is leaking fuel out onto the outside of the manifold on either side of the carb, it is usually due to fuel dribbling out the main discharge nozzles after engine shutdown, splashing onto the throttle plates, and siphoning out the throttle shafts. Like on the Holley, this is usually due to poor float level fuel control from a leaky needle/seat; a sticky needle or hung up float; excessively high float level; a fuel saturated float; or fuel boiling in the float bowl.
Also of note on the Q-Jets: Every so often I see people with problems with fuel leaking out of the upper (air horn) gasket, thinking that the gasket just needs to be changed. On a correctly set up Q-Jet, the upper gasket should never be soaked with fuel, and fuel should never touch the gasket except due to occasional fuel sloshing from cornering/acceleration/braking. If fuel is soaking the upper gasket with the vehicle at rest, there is a fuel level control problem.
Thread Starter
Pro
Joined: Jul 2002
Posts: 589
Likes: 8
From: Palm Bay FL
Re: Carburetor leakage! (lars)
Guys -
If a Holley carb has fuel puddling on the intake manifold, it is almost always from fuel dripping out of the throttle shafts after engine shutdown. This fuel comes from fuel being discharged out of the main discharge nozzle after engine shutdown: the fuel dribbles out the discharge nozzles, hits the throttle blades, and leaks right out the sides of the throttle shafts and onto the intake manifold.
Cause for this is one of the following:
1. Leaking needle/seat (replace needle/seat or rebuild carb)
2. Float level too high (adjust float levels with engine hot and running)
3. Fuel boiling in float bowl after shutdown (not much you can do about the new fuels with ethanol additives - the fuel has a lower boiling point than the old fuels)
4. Ruptured power valve (replace PV or rebuild carb)
5. Bad o-ring on accel pump transfer tube (rebuild carb)
The metering block gaskets very seldom just start leaking - these are really fail-proof connections. Once in a while you'll get an accelerator pump gasket leak, but this is also rare. I'd start with doing a hot float level setup. After shutdown on a hot engine, remove the air cleaner and take a look down the venturi and see if you can see fuel percolating out of the main discharge nozzles. If you can, you hae one of the other problems noted above.
If a Holley carb has fuel puddling on the intake manifold, it is almost always from fuel dripping out of the throttle shafts after engine shutdown. This fuel comes from fuel being discharged out of the main discharge nozzle after engine shutdown: the fuel dribbles out the discharge nozzles, hits the throttle blades, and leaks right out the sides of the throttle shafts and onto the intake manifold.
Cause for this is one of the following:
1. Leaking needle/seat (replace needle/seat or rebuild carb)
2. Float level too high (adjust float levels with engine hot and running)
3. Fuel boiling in float bowl after shutdown (not much you can do about the new fuels with ethanol additives - the fuel has a lower boiling point than the old fuels)
4. Ruptured power valve (replace PV or rebuild carb)
5. Bad o-ring on accel pump transfer tube (rebuild carb)
The metering block gaskets very seldom just start leaking - these are really fail-proof connections. Once in a while you'll get an accelerator pump gasket leak, but this is also rare. I'd start with doing a hot float level setup. After shutdown on a hot engine, remove the air cleaner and take a look down the venturi and see if you can see fuel percolating out of the main discharge nozzles. If you can, you hae one of the other problems noted above.
[Modified by mpro72vette, 3:22 PM 7/18/2002]
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Carburetor leakage! (mpro72vette)
mpro-
Another small piece of advice:
If you decide to rebuild the carb and to put a kit in it, make sure you buy a real Holley kit - not a kit made by Echlin, Big-A or one of the others. Echlin makes good Q-Jet kits, but really bad Holley kits. Only the Holley kits have the correct needle/seats in them, the correct power valves, and the good non-stick gaskets. Holley kits are not cheap anymore, but places like Summit & Jegs have fair prices on them. You will need to note your carb list number when ordering the kit.
Another small piece of advice:
If you decide to rebuild the carb and to put a kit in it, make sure you buy a real Holley kit - not a kit made by Echlin, Big-A or one of the others. Echlin makes good Q-Jet kits, but really bad Holley kits. Only the Holley kits have the correct needle/seats in them, the correct power valves, and the good non-stick gaskets. Holley kits are not cheap anymore, but places like Summit & Jegs have fair prices on them. You will need to note your carb list number when ordering the kit.
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Drifting
Joined: Feb 2001
Posts: 1,603
Likes: 0
From: San Francisco, CA
Re: Carburetor leakage! (mpro72vette)
Go for the rebuild! I did it for the first time last spring on a Quadrajet and it is not a huge deal if you stay really organized and take your time. I basically spent all weekend on it on and off, but got it right the first time - way too long by the way but will go faster the next time. gtr1999 suggested that I build a little stand for the carb which really helped. Take a board and put four 6in. x 5/8in (I think) carriage bolts through it and thread nuts on them an inch down or so. Basically, replicate the way the carb is bolted onto the manifold but it just sits on the bolts. With the carb on the stand you can work the throttle linkage freely and it holds the carb nicely for assembly, inspection etc. Good luck :cheers:
