General Category > Quadrajet Carb Talk and Tips

q-jet idle

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prostreet64:
Good morning one and all. I posted this question over on PY but no responses yet. Anyway, I have a q-jet that the rpm will hang at 1500 when I blip the throttle. I have the idle set at 900-1000 when I first rev the motor. I am then manually closing the throttle against the fast idle stop to make sure it is closed, but the idle hangs at 1500. If I back off the idle screw the idle will come down and then I can reset it at 900. If I repeat the test I get the same result. Fuel pressure is at 7-7.5 psi; could this be causing the needle to stay open? This carb was rebuilt several years ago  by an unknown party and then put on the shelf so it hasn't been run in a longtime. Other things to look for? Thanks.

gtome:
Any chance the butterflys are hanging up on the intake? I had one act like that before and thats what it was doing. Mine had a 4 hole spacer on it just FYI.

prostreet64:
I thought about that but I was manually closing the throttle linkage at the carb  to make sure nothing was hanging up on the spacer. Even before that I had looked down the throat and worked the butterflies full open to make sure that everything was moving freely.

429bbf:
fwiw is there a chance that its hanging on the fast idle cam . that what it sounds like.dean

motorvation2go:
Good points for investigation have been suggested.
Having eliminated(?) these as the source of problems, I can't help but think of vacuum leaks (hoses, carb to manifold, manifold to heads, over enthusiastic drilling of holes in primary throttle butterflys)...
*** Also gnawing at the back of my ol' noggin is the possibility that you're running [too] light centrifugal advance springs in your distributor (and/or sticking weights) which might be causing your timing to 'hang'.
I'm sure Cliff will have better insight into your situation... but the timing issue deserves consideration.
Good luck with the chase...

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