Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

17085292 Idle Speed

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Raoul Ross:
85 Chev C10 Suburban. I cannot get the idle speed down. Idle speed is 900-1k

Idle speed screw is completely backed off tab. Unit was rebuilt at least once, the mixture screws are exposed. Timing is set to spec. Butterflies are closed on secondary side. Vacuum is 20in. at idle. It has a mixture solenoid but no TPS.

Kenth:
Vacuum leak or still on fast idle cam?

quadrajam:
Is the choke fully off and the fast idle cam out of the way?(Adjustment screw down low on passenger side)
Maybe a small vacuum leak?
Check that the throttle cable and trans cable are not tight at idle.
Make sure the link between primary and secondary shafts is not tight at idle.
Has the idle bypass air been modified?
Manifold or ported vaccum to advance can?

I have a couple of that same carb and no such problem.

QJ

Kenth:
BTW, this carb has no mixture solenoid.
It has the ordinary power piston, metering rods and jets.
The solenoid used is for the "dual capacity pump" feature.

Raoul Ross:
Excellent point about the throttle/trans cables, I will definitely look into that!

I looked at the secondary linkage, plenty of slack there, definitely in spec. There doesn't seem to be any slack in the throttle shafts either. 20in. of vacuum at idle tells me it's not a vacuum leak.

Manifold vacuum to dizzy at idle. When pulled (to check timing) vacuum goes down to 12ish inches though I didn't plug it. I just wanted to check that somebody hadn't bumped the timing up. We usta do that 'Back in the Day' to impress the customer with your tune-up expertise!  8)

Dual capacity what?  :-\

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