Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Q-Jet 17057274 idles too fast

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beertracker:
Problem:

Q-Jet 17057274 idles at 1500 rpm.  It's on a 75 Pontiac 400 with stock 6x-8 heads, stock cam, stock dual exhaust, auto trans. 

It has idled too fast every since I bought the car and I cannot slow the idle down by adjusting the idle mixture screws either in or out or the idle speed screw.  The fast idle cam is in the down position so it's on slow idle.   There is an air gap between the throttle stop and throttle stop screw so the primary throttle is fully closed.  If I manually  open the secondary air flap just a small amount the engine will slow down but as soon as I let go of the air flap the engine speeds up.  The carb does not have a bushing kit installed

I installed a rebuild kit from Cliff and this did not solve the fast idle problem.  I believe the kit had either .037 or .038 idle tubes.  During the rebuild I did not touch the primary or secondary throttle shafts or  plates.  I carefully set the new float to 1/4" at the toe.  I used the green spring for power pump return.  Primary rods and secondary rods were carefully inserted in to their respective jets.

After I get the fast idle problem solved I am going to install milled (.040") Pontiac 6x-4 heads, Summit headers and a Summit 2802 camshaft.

I need some ideas what to do next to solve the fast idle problem.

Thanks,
BT

Toronado:
When the cars off, are the primary throttle flaps closing all the way,
and is the throttle stop sitting on the idle screw? Could be the vacuum pulling it open
because an incorrect adjustment. If there is a gap on the throttle stop when it is off then just look and see if something is binding and preventing it from closing. Either its binding, or being held open to far because incorrect adjustment.

Cliff Ruggles:
Remove the baseplate and hold it up to a light.  All the throttle plates should be fully closed.

The air has to be coming from someplace, either leaking around the secondary throttle plates, or a big vacuum leak someplace?.....Cliff

beertracker:
The "idles too fast problem"  has been with engine running without an air filter installed in the garage.  Is this ok?  Would carb idle speed change depending if a air filter is used or not?

Thanks,
BT

Cliff Ruggles:
Not really, idling that fast is air getting in under the throttle plates.....Cliff

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