Pre-Ignition condition
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Instructor
Joined: Jul 2006
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From: Hamden CT
St. Jude Donor '12
Pre-Ignition condition
69 Stingray with 496" big block, Holley 850 DP, DUI Distributor. Whenever I shut the car off after a fairly long drive I get some pre-ignition (or is it post ignition?). I'm thinking it's either that the carb is running too rich and still dumps some gas down the intake after turning the key off or possibly the ported vacuum port on the carb that goes to the distributor is pulling some vacuum at idle/low rpm.uys
What do you guys think? Any other ideas?
Thanks all!
What do you guys think? Any other ideas?
Thanks all!
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The number one cause for this run-on condition is the idle being set too high.
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
That's correct. Lower your idle speed as much as possible. You might also check your transition slot exposure on the carb and make sure you are not exceeding .020" exposure on the primary side. If so, balance out the idle speed with the secondary idle speed screw to reduce transition slot exposure. This will smooth out your idle, allow a lower idle speed, and will pull less fuel through the transition slots after shutdown.
Lars
Lars
Thread Starter
Instructor
Joined: Jul 2006
Posts: 208
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From: Hamden CT
St. Jude Donor '12
It seems to be a little better if I let it idle for 15-20 secs before shutting her off.
Last edited by ja1724; Jul 2, 2010 at 01:56 PM.
Thread Starter
Instructor
Joined: Jul 2006
Posts: 208
Likes: 0
From: Hamden CT
St. Jude Donor '12
That's correct. Lower your idle speed as much as possible. You might also check your transition slot exposure on the carb and make sure you are not exceeding .020" exposure on the primary side. If so, balance out the idle speed with the secondary idle speed screw to reduce transition slot exposure. This will smooth out your idle, allow a lower idle speed, and will pull less fuel through the transition slots after shutdown.
Lars
Lars
Jim
