high idle with temperature increase
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Joined: Mar 2007
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From: King Of Prussia Pa
high idle with temperature increase
I have a 75 coupe. I'm using a GM Performace Parts 350/330 crate motor. This came with a Holley 600 which I used for over a year but wasn't happy with it. ONE of the problems was that as the engine temperature increased say 200/220 degrees and if I came to a stop my idle would be up around 1100 RPM in drive. When the temp got back to say 160/170 the idle would be fine. I'm using an electric fan. There is no a/c solenoid to kick the idle up and I had an electric choke. I switched to my rebuilt Quadrajet and what a difference. that carb woke that motor up big time. Now this is doing the same thing. High Idle at Higher temperatures, normal when the temperature goes down. Now I havn't pulled over and checked to see where the idle screw is or if it's on the high idle screw of the choke. Electric choke conversion on the Quadrakjet too. No other problems with the carb. Any Ideas?
Le Mans Master
Joined: Oct 2000
Posts: 8,897
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From: Santa Ana CA
If it does it with two totally different type carbs, as you suggest, I would be looking towards a vacuum leak possibly due to an improper seating (carb base, intake manifold, intake manifold fitting, etc.) somewhere that possibly expands and/or warps due to heat causing a vacuum leak with elevated temps.
Perhaps when this problem is manifesting itself, you could use carb spray, an unlit propane torch, etc. in various areas to isolate the problem.
Perhaps when this problem is manifesting itself, you could use carb spray, an unlit propane torch, etc. in various areas to isolate the problem.
Race Director
Joined: May 2006
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From: Dayton, Ohio
Lars will hopefully come in and make sense of this but I seem to remember the TCS switch would send vac to the dist when the engine got hot to raise engine idle but your probably not running the TCS.
I've had too high of fuel level cause fuel to dribble in the primary's but I think that caused a lower idle.
Ive had a too tight accelerator cable cause a high idle when hot but don't remember exactly why the heat was a factor.
Cruise control is another factor in idle depending on the linkage setup.
I wonder if heat could effect in some way the ported vacuum signal to come in while the throttle plates are still closed ?
Grasping but at least its a bump for you.
I've had too high of fuel level cause fuel to dribble in the primary's but I think that caused a lower idle.
Ive had a too tight accelerator cable cause a high idle when hot but don't remember exactly why the heat was a factor.
Cruise control is another factor in idle depending on the linkage setup.
I wonder if heat could effect in some way the ported vacuum signal to come in while the throttle plates are still closed ?
Grasping but at least its a bump for you.
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Joined: Mar 2007
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From: King Of Prussia Pa
I'm with you guys thinking in the lines of vacuum. NO TCS switch being used. No a/c solonoid. Throttle cable is actually a little loose, need to tighten this after this problem is solved. I'm also thinking maybe distributor weights sticking open. It's strange for sure. Tomorrow will be test day depending on what other topics are hit on.
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Team Owner
Joined: Jan 2006
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From: Crossville TN
If the line going to the vaccum advance is only rubber line, it could be collapsing at max vacuum and prevent that vacuum signal from ever getting to the distributor. Most systems use 3/16" or 1/4" hard line for the distributor advance system, except for some rubber tubing at each end.
Burning Brakes
Joined: Dec 2004
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From: Hanging out back with the dark horses. Wa.
If the line going to the vaccum advance is only rubber line, it could be collapsing at max vacuum and prevent that vacuum signal from ever getting to the distributor. Most systems use 3/16" or 1/4" hard line for the distributor advance system, except for some rubber tubing at each end.
I'm thinking more along the line of timing. have not read where you put a light on it. that will tell you if the advance is stuck or not. You can also put a hand pump on the line and see if it's working.
might also be to light of advance springs
