Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Can't get idle down. Several cases...

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Marx3:
Yes I this was the only way to lower the idle below 7-800.
Not in any way ideal, I know.
So I guess the recipes ARE too generous.
The weird things is, one carb was a early 80's Chevy unit, one was the original 1976 Cadillac unit and one was an oddball 7045186. That one was definitely some sort of service replacement or rebuild unit.
It had main air bleeds about 4-6 mm ( 5/32"-15/64" ) long, making them stick out of the air horn and Venturi.
My point is, that these were 3 completely different carbs, set up the same way on the same engine. And 2 of them had the exact same problem.

Cliff Ruggles:
Too much timing on a basically stock engine can do the same thing.  If you are running a lot of timing and manifold vacuum to the advance on a big 500 Caddy engine you could loose control of the idle speed as it would be sucking pretty hard on the entire intake system. 

The engine still has to get air from someplace, and if all the throttle plates are tightly shut at idle, then bypass air is all that is left, aside from the little bit of air it gets from the PCV system.....Cliff

Marx3:
The first engine was at ~18 degrees initial with ported vacum if I recall correctly, and that did not give me any trouble keeping idle lower than 800.
The two other engines had 15 degrees initial, but can't remember if VA was manifold or ported.
I see your point though. I will check if it helps to put the VA on a ported source.

Actually I am having the same problem on my stock SBC.
The carb is calibrated for the 214/224@050 cam I am about to install ( along with 10:1 cr ).
.036 tubes
.051 DCR
.070 IAB
.085 mixture holes
.065 bypass.
Going to ported VA helped get the idle down to 700 rpm with 17 degrees initial.

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