[Delawarebird]

First let me say I haven’t owned a vehicle with a quadrajet for a very long time. That being said I recently purchased a 1978 Trans Am with a pretty stock L78 400. Gave the car a complete tune up and had the original quadrajet rebuilt. Problem since day one has been from a standstill if I put the peddle to the floor the car falls flat and sometimes stalls out. Running down the road if I ease the peddle down I can feel when I hit the secondaries and the car has a slight stumble then goes. I moved the accelerator pump shaft closer to the carb for a longer pump shot with minimal to no difference. Car is pretty responsive for a car with 2.41 gears as long as you stay out of the secondaries. Have also tried tightening up the secondary spring, currently at about 3/4 and they feel pretty stiff. Side note vacuum advance is on manifold port, seems to run better there than on ported. Any thoughts would be appreciated, just not sure if the problem is too much fuel or not enough

[242177P]

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[foxgapLeMans]

I had the same type problem my Q jet on my 71 400. I called Cliff at Cliff's Automotive and got a rebuild kit from him. Use the book Cliff wrote to follow his recipes on rebuilding the carb and you will not be disappointed. GM leaned these carbs out so bad they will not run on todays gasoline. We rebuilt my carb and is like night and day in the performance of the engine.

[Delawarebird]

I did buy Cliffs book and have started to read through it. Not sure of my confidence if I have to make modifications to the carb. Might purchase his kit and plan on doing the rebuild in the fall. Car does run and would like to enjoy it while the weather is nice to shake out any other issues. Did you have to drill out anything or make any major modifications to yours?

[JSchmitz]

You might have a bad choke pull-off diaphragm. The secondary air valve spring is only part of what controls secondary opening rate. More significant is the orifice inside the pull of diaphragm. If the diaphragm is bad, it will fly open very fast and cause a stumble. Remove the vacuum line. Depress the diaphragm and hold your finger over the vacuum port. Now release the diaphragm. It should stay in until you remove your finger. Or you can test it with manifold vacuum or hand vacuum pump.

[Delawarebird]

Thank you, I did check that. Holds fine and takes about 2-2 1/2 seconds to fully release. Found what I think was part of the problem, the choke was a little loose allowing primary blades to close down a bit. Reset everything back to square one, secondary spring at about 1/2 turn after contact. Noticed I could get the secondary blades to just crack open and shoot a small amount of fuel if I hit the throttle fast in park. Noticed at idle secondary blades not completly locked, very small amount of play. Bent rod just a hair to make sure blades are closed when they should be. Car seems to run better but at a standstill and mashing the gas it still stumbles, I believe it’s flooding because I can smell fuel.

[foxgapLeMans]

I think we drilled out only one item on the list. Everything else was within tolerance. Cliff asked what my cam was, the CI of the motor and the number of the carb. Also what trans I had. The book recommended some mods to the idle springs which worked out great. Cliff asked if I had a stumble getting into the secondary's , which I did, but after the rebuild no stumble anymore.