Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Quadrajet runs better without accelerator pump.

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Mudsport96:
What is your vacuum at idle?
And I'm thinking you need to go through your rod and jets sizes on the primary side. I had a similar problem and ended up going down in jet size and giving it a little more timing that brought my vacuum up. My rods were raising to early and dumping fuel as soon as I hit the throttle.
And if you don't know what rods you have, it could be anything. Is this a factory carb? Or is it a remanufactured carb?

NathansCorvette:

--- Quote from: Mudsport96 on November 22, 2024, 10:52:55 AM ---What is your vacuum at idle?
And I'm thinking you need to go through your rod and jets sizes on the primary side. I had a similar problem and ended up going down in jet size and giving it a little more timing that brought my vacuum up. My rods were raising to early and dumping fuel as soon as I hit the throttle.
And if you don't know what rods you have, it could be anything. Is this a factory carb? Or is it a remanufactured carb?

--- End quote ---

My vacuum at idle is around 16". That sounds about right. As soon as I touch the throttle fuel seems to pour out. With the accelerator pump, it was even more. I will disassemble any look at the rods when I get the chance.

It is not the original qjet to the car, but it is not reman'd. I did rebuild it myself. See my post below.

NathansCorvette:
I should note that my Corvette has a non-original qjet on it. According to the service log I have for it, when it was first barn-found, somebody put a Holley carb on and the original qjet got lost to time. The fellow I bought it from had bought a used 1974 qjet online, I believe he said from a 1974 Camaro, and installed it.

By the time I bought the car, 15 years had past and I rebuilt this non-matching carb with Cliff's kit and by Lars' guide. By looking at the internals and the state of the finish on the outside, I am confident that it is not a remanufactured unit. Mind you, it was never in bad shape, and is super clean after my rebuild.

The carb stamping is 7044502BM. This means its from a 1974 auto trans chevy with California emissions. Could it be that it being a cali emissions carb on a non-cali engine that it could be causing issues? Also my Corvette is a manual, but I doubt that would affect anything...

Kenth:
According to my notes, there are not big enough differences between 7044502 and for example 7044211 to cause the symptoms you are experiencing.

A too large inlet needle valve seat combined with too high fuel pressure will raise fuel level in bowl and start fuel delivery sooner than intended.

Cliff Ruggles:
I'd start by looking at parts directly related to the problem.

Idle tube size?  DCR's, upper/lower IAB sizes, jet size, primary metering rod size, and the power piston hanger arms. 

Since the carb is not original and unknown origin it could be something as simple as the jets were drilled out, worn out, or too big for what you are doing.  Most carbs that come in here have bent power piston hanger arms leaving the primary rods WAY too high in the jets.

If the post is still present on the power piston check the power piston height.  Maybe someone bent the APT arm in the baseplate and the piston is too high.

Those carbs are known for being lean, especially the CA versions and on this new fuel there is no reason it's so rich right off idle that adding any fuel from the accl pump is causing a rich stumble......

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