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I have the original Quadrajet carb for this 76 Vette. I took it off, took the top off and it’s already been rebuilt. So I replaced the gaskets and put it back together and put it back on the car. Now I can’t get the car to idle or run right for very long periods of time. I’ve adjusted the choke to where it should be. I’ve turned the idle screws in and out all the way to 6 turns out and nothing changes with how it runs. It runs when I push the choke blade down and sometimes it runs for 20 mins or longer. It seem like if I’m having to choke it off it running lean. My first thought was a vacuum leak, but I plugged off every line individually and nothing ever changed. I thought I had it running good the other day because we were able to drive it around town with no issues. But clearly something’s off. This video shows what its doing.
The video is private so you have to click this link every time you go to watch it.
Not a Quadrajet pro by any means but the fact that manually moving the choke sorts it out tells me it’s surging because the air fuel ratio is wrong.
There might be something else wrong but I would first make sure the choke is operating as it should. If the choke is right then I would start looking for other issues like a vacuum leak.
Other folks might have better suggestions but I would start there.
Contact forum member Lars.
He is the worlds guru for the QJets on our Corvettes.
If it’s repairable, he’ll tell you how and if it needs rebuilding he is the only person to send it to.
Contact forum member Lars.
He is the worlds guru for the QJets on our Corvettes.
If it’s repairable, he’ll tell you how and if it needs rebuilding he is the only person to send it to.
Ok, I will. How do I contact him? I'm newer to this forum and I don't know how to contact somebody.
Ok, I will. How do I contact him? I'm newer to this forum and I don't know how to contact somebody.
From his CF stats page:
Everyone:
If you need tech assistance, please e-mail me on my tech e-mail line at: V8FastCars@msn.com
I don't keep up with these message boards on the various Forums.
Thanks!
Lars
Why did you take the top off ? Was it running bad before you took the top off or is this a new problem?
If I had to guess is the primary metering rods got relocated away from the jet when the top was removed and gasket replaced
Why did you take the top off ? Was it running bad before you took the top off or is this a new problem?
If I had to guess is the primary metering rods got relocated away from the jet when the top was removed and gasket replaced
It was running very good before I took it off. I noticed that I had gained about a quart of oil and it smelled like gas. My first thought was fuel pump, but my grandfather who used to be a mechanic in the 60s and 70s told me to first pull the carb and check to see if the float level was to high, causing fuel to run down the cylinder walls, mixing with the oil. I can’t quite remember if that’s exactly what he said but I think it was that. He also said to check the plugs on the bottom of the carb to see if they were leaking fuel. He suggested that while I have the carb out I may as well rebuild it. So I took the top and bottom of the carb off and it has new parts in. So I put new gaskets in and put it back together. Then it ran like crap. My grandpa helped me rebuild it and he’s stumped about what the problem is as well.
If you purchased a carburetor kit from one of the big box stores there are normally 2 or 3 different air horn gaskets.
Are you 100% positive you selected the exact match for your application?
I also see that the EFE TVS vacuum switch has been deleted (That's OK) but the vacuum port on the carburetor is open and should be capped off...That is a major vacuum leak as it is Full Manifold Vacuum...
There is also a tightening sequence that should be followed when re-installing the air horn, those instructions should have been included with the carb. Kit...Or maybe Not .
Looking at the rebuild kit part numbers in the GM parts book it looks as if your 76 L82 manual trans uses the same kit as my 77 L48 AT.
"IF" your carburetor is original the air horn gasket should be the same, notice the extra hole in the gasket on the right that serves no purpose.
That's just the way they come now, I get my kits from Cliffs High Performance.
Photo for reference if you desire to match yours.
From: At my Bar drinking and wrenching in Lafayette Colorado
Carter - The first thing I'm seeing on your carb is that you are getting severe exhaust gas reversion sooting up through your intake and through the carb (your choke is black). This is an indication of significant engine tuning issues not related to the carb - most often severely retarded timing combined with possible inoperable vacuum advance. A well-running carb cannot compensate for badly set timing, so you need to first fix your timing problem.
That's not to say you don't also have a carb problem - you do.
You have a fuel level control problem, with fuel discharging from the main discharge nozzles at idle. This fuel hits the throttle blades and wicks out the throttle shaft to cause the dripping you see. It also wets the airhorn gasket and causes your idle mixture screws to be non-responsive. It has nothing to do with the airhorn gasket itself.
Fuel level control problems can be caused by the following issues, among other things:
Incorrect float installed
Defective float installed
Float or float arms binding on bowl casting walls
Float level incorrectly set
Float hinge pin not correctly arched
Float needle clip incorrectly installed
Dirt in needle/seat
Seat gasket improperly installed
Incorrect needle/seat assembly installed
Excessive fuel pressure/defective fuel pump
All these issues need to be checked and corrected.
However, you indicated that the carb had been previously rebuilt. If your carb is a commercially rebuilt carb (I can see indications of commercial hardware installed in the carb in your photos above), your carb will have at least a dozen other serious problems that need to be identified and corrected.
Bottom line: You have a parts problem or a workmanship problem (or both) on your carb. It needs a complete disassembly, cleanup, and thorough inspection to identify the issues, and a proper rebuild with good quality parts and a proper setup.
Originally Posted by bmotojoe
I also see that the EFE TVS vacuum switch has been deleted (That's OK) but the vacuum port on the carburetor is open and should be capped off...That is a major vacuum leak as it is Full Manifold Vacuum...
I agree. You have an uncapped port on the carb, and it's sucking air and further causing you more problems - you have a vacuum leak, which will cause an inconsistent idle. It won't cause the fuel level control problem you have, but it's contributing to your issues - you have multiple problems.
Lars
If you purchased a carburetor kit from one of the big box stores there are normally 2 or 3 different air horn gaskets.
Are you 100% positive you selected the exact match for your application?
Yes, I am very sure I got the correct one. I matched up the old one with the new one and made sure I could see light though all the holes. I forgot where I got the rebuild kit. It was online. It did come with a bunch of options.
Originally Posted by bmotojoe
I also see that the EFE TVS vacuum switch has been deleted (That's OK) but the vacuum port on the carburetor is open and should be capped off...That is a major vacuum leak as it is Full Manifold Vacuum...
Yes, in the video it was unplugged. I must’ve forgot to plug it in. But I have had it plugged the whole time.
Carter - The first thing I'm seeing on your carb is that you are getting severe exhaust gas reversion sooting up through your intake and through the carb (your choke is black). This is an indication of significant engine tuning issues not related to the carb - most often severely retarded timing combined with possible inoperable vacuum advance. A well-running carb cannot compensate for badly set timing, so you need to first fix your timing problem.
That's not to say you don't also have a carb problem - you do.
You have a fuel level contrrol problem, with fuel discharging from the main discharge nozzles at idle. This fuel hits the throttle blades and wicks out the throttle shaft to cause the dripping you see. It also wets the airhorn gasket and causes your idle mixture screws to be non-responsive. It has nothing to do with the airhorn gasket itself.
Fuel level control problems can be caused by the following issues, among other things:
Incorrect float installed
Defective float installed
Float or float arms binding on bowl casting walls
Float level incorrectly set
Float hinge pin not correctly arched
Float needle clip incorrectly installed
Dirt in needle/seat
Seat gasket improperly installed
Incorrect needle/seat assembly installed
Excessive fuel pressure/defective fuel pump
All these issues need to be checked and corrected.
However, you indicated that the carb had been previously rebuilt. If your carb is a commercially rebuilt carb (I can see indications of commercial hardware installed in the carb in your photos above), your carb will have at least a dozen other serious problems that need to be identified and corrected.
Bottom line: You have a parts problem or a workmanship problem (or both) on your carb. It needs a complete disassembly, cleanup, and thorough inspection to identify the issues, and a proper rebuild with good quality parts and a proper setup.
Lars
Thank you. I’m gonna set the timing correctly, I’ve known it’s been off but I didn’t know much it’s off. I’ll also take the carb apart, clean it up and try to diagnose the problems.
CarterDawson
I have the original Quadrajet carb for this 76 Vette. I took it off, took the top off and it’s already been rebuilt. So I replaced the gaskets and put it back together and put it back on the car. Now I can’t get the car to idle or run right for very long periods of time. I’ve adjusted the choke to where it should be. I’ve turned the idle screws in and out all the way to 6 turns out and nothing changes with how it runs. It runs when I push the choke blade down and sometimes it runs for 20 mins or longer. It seem like if I’m having to choke it off it running lean. My first thought was a vacuum leak, but I plugged off every line individually and nothing ever changed. I thought I had it running good the other day because we were able to drive it around town with no issues. But clearly something’s off. This video shows what its doing.
The video is private so you have to click this link every time you go to watch it.
Great advice by all. I would add that if you are a quart up in the crank case, it may be fuel. On many levels, that can spell disaster for your engine. Change the oil. Jerry
...and if you want me to check out the carb, just send it out and I'll run it on the test stand engine and provide you with results.
Lars
Thank You. I’ll try to figure it out myself first, but if I don’t get anywhere I will. I’m out of town so I won’t be able to work on it for a few days.
Terrible Idle. What’s wrong?
