high and low idle - Chevelle Tech
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post #1 of 2 (permalink) Old Apr 13th, 11, 12:37 PM Thread Starter
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Join Date: May 2009
Location: clutch linkage problems
Posts: 85
high and low idle

I have a 454-Oval Port Heads-Crane Cam (not sure specs)-edelbrock intake-holley 750 double pumper-hooker headers. The car has a Muncie M21.

I recently installed a new MSD Street Fire HEI distributor. I set the initial timing at 14 with the vacuum advance disconnected.

When I first start the car, with the vacuum advance connectred, it is extremely "cold blooded" and is hard to keep running. When the car "warms up" it either idles high (1,500 rpm) to low (500 rpm). No matter how you set the carb, it keeps idling this way. The car seems to run ok.

If I disconnect the vacuum the idle is fine. The car runs fine until I get around 3,000 rpms and then it starts to miss. It also will pre-ignite on occassion.

I have installed a new set of AC Delco Rapid Fire plugs to no avail. The spark plug wires are new MSD.

I have tried to adjust the vacuum timing through the vacuum advance cannister but can not seem to locate the 5/32 hex adjusment.
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post #2 of 2 (permalink) Old Apr 13th, 11, 2:37 PM
Tech Team
Join Date: Apr 2010
Location: Fullerton, CA
Posts: 526
Re: high and low idle

Try checking the springs inside the distributor. I had this problem with my 383 and I thought it was the carb, but when I talked to Sean Murphy (I have one of his Quadrajets) he said it may still be getting some advance if the springs are too light or if they are gummed up. I changed the springs and everything is fine now.

1972 Chevelle
383 stroker
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