Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Idleproblems on my Cadillac 500 stroker

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MonteCarlo:
Hi. I am new at this forum but I give it a try.

Have a Cadillac 500 stroker 540 CID with rollercam .600 lift 237 duration 112 LSA. 10:6 compression. Ported heads bigger valves edelbrock intake etc.

Quadrajet 750 17059216 rebuilt in Sweden from a good workshop.

Ignition base 16 max 35   10 degrees vacuum advance.

The engine seems to pull approx 10 hg.

My problem is that I have to give it huge amount of bypass air to get it idle. I have done that througt a controlled vacuumleak (1/4 inch) together wit 0.135 bypass air. With the mix screws out about 6 turns it working but it not feel right because of that big extra hole. The butterflyes open about 1 turn, think it is pretty much ok for the transition slot. Idle between 900-1000

Specs:
Idle tube: 0.04
Restriction: 0.064
Upper air: 0.071
Lower air: 0.071
Holes in baseplate: 0.96
Idle bypass: 0.135

I think it should idle without the extra bypass througt the extra nozzle. I read in another thread where a guy had simular problems that the airbleeds was to big and that it was better to move the upper airbleed up to the horn?
happy to get any suggestions. Ready to give up ;)

Erik Olsson Stockholm Sweden

77cruiser:
That's what I did move the idle air bleed to the air horn. Drill from the bottom the hole is already started. 6-32 brass set screws 1/8 inch long. You'll plug the original bleeds.
This is how I did mine, not my pics though.

MonteCarlo:

--- Quote from: 77cruiser on September 18, 2017, 08:47:17 AM ---That's what I did move the idle air bleed to the air horn. Drill from the bottom the hole is already started. 6-32 brass set screws 1/8 inch long. You'll plug the original bleeds.
This is how I did mine, not my pics though.

--- End quote ---

Thanks, i think I try that. Was this a big inch engine to?

77cruiser:
421 SBC idles with about 12 " vac.

Cliff Ruggles:
That vacuum reading seems low to me for the CID, compression and cam specs.

Anyhow, did you try tipping in the choke flap or gently placing your hand over the choke housing to richen it up some at idle?  If the engine responds well to this it may simply need more idle fuel instead of a bunch of idle bypass air, and may like a little of both.

With .096" holes under the mixture screws you're probably at or close to maxed out on idle fuel delivery with the screws backed out 6 turns (metric threads).

I'd do the test mentioned above before blocking off the upper idle bleeds and moving them to the airhorn as it's always best to determine if the engine actually needs more fuel, or more bypass air before drastic changes to the original set-up.......Cliff

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