Quadra-jet idle problem
I've got a problem with my '72 SB idling properly. When I first start the car the chock does it's job and the car idles fine for the first mile or so after warmup. However, after the engine is up to full operating temp. the idle speed is about 1200 rpm. I've got two springs (inner and outer) on the idle control arm to help pull the idle down, but everything I've tried so far has failed to solve my problem. And, no, I don't want to put a Holley on. Anyone out there have any suggestions?
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Kurt Geis
Chairman, Midway USA Chapter
Targa Blue 1972, Top Flight and Duntov Award, 2014
Arctic White 1994, Top Flight, Hrt. of Amer. Reg. 2011
Arctic White 2013 60th Anniv Special Edition Conv. -
Re: Quadra-jet idle problem
if the choke is clear open you have a problem with the choke linkage not coming off of the fast idle cam -
Re: Quadra-jet idle problem
I agree, there is a small colil spring that ensures that this happens properly. Check and make sure that spring hasn't slipped, or is broken. You can also try to clean and lubricate all the linkage componants that control the fast idle cam.Comment
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Re: Quadra-jet idle problem
kurt,
Are you saying the throttle arm is not returning to the idle adjust screw or do you mean the screw is backed out and the engine still idles fast?Comment
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Re: Quadra-jet idle problem
The throttle arm is not returning to the idle screw. The chock is working fine. That was my first suspect. For some reason the throttle linkage won't return all the way to the icle screw.Kurt Geis
Chairman, Midway USA Chapter
Targa Blue 1972, Top Flight and Duntov Award, 2014
Arctic White 1994, Top Flight, Hrt. of Amer. Reg. 2011
Arctic White 2013 60th Anniv Special Edition Conv.Comment
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Re: Quadra-jet idle problem
Kurt,
The problem may be wore throttle bore if the choke is open and all linkage is clear. Do you know how many miles on the carburetor?
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Re: Quadra-jet idle problem
I'm not sure that the carb screw is the primary means of controlling idle speed on a '72. Do you have an electrical solenoid on the left front of the carb? If so, the plunger must be adjusted, not the carb.Comment
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Re: Quadra-jet idle problem
OK, it's not rocket science! You can play with it, find the problem(s) and fix...
The way the carb is designed is for the choke rod to lift the choke plate to its cold start closed position AND swing the high idle cam up to its cold-start engaged position. These actions (which step of the high idle cam does the throttle stop on and how far does the choke plate close) are dictated by straightness/bend of the choke rod and the high idle adjust screw.
As the engine warms and the choke's bi-metal changes dimension, the choke plate and the fast idle cam are supposed to release. The fast idle cam has a counter weight arm that 'should' pull it down with gravity and progressively slow the idle RPM until the cam is totally released and the carb returns to its normal curb idle setting.
IF the carb was re-assembled incorrectly and the fast idle cam mechanism is installed backwards, you've got a problem! Next, the fast idle cam adjusting screw may be mis-adjusted causing it to hold the cam up/in-place too long. Last, you can develop 'gunk' on the moving parts that cause them to stick (a spritz of carb cleaner solves this).
Soooooo, you diagnose by getting the engine warm/hot and with your fingers FORCE the fast idle cam to its engaged position. Now, move the throttle cable to momentarily rev the engine and you ought to see the fast idle cam fall down and release on its own due to gravity.
If it doesn't self-disengage, the odds are good you're fighting one of the three 'cockpit' problems I described....Comment
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