Idle problem, please help
Thread Starter
Advanced
Joined: Mar 2003
Posts: 98
Likes: 3
From: Oglesby Illinois
Idle problem, please help
I have a 70 Corvette, manual, 454 LS5 I recently rebuilt. Car ran fine before, short of the broken piston 
After rebuild the car doesn’t feel like it has quite the same performance although I haven’t ran it hard due to break in period. Also it will not idle very well my biggest concer..some times 1000 or 700(ideal) or 1200 also when not at operating temp will die when taken off of choke, previously car would still idle fine. Timing is dead on where it was before, I have plugged the intake vacuum line to verify no vacuum leaks…the compression is fine although about 10% higher than before. The carb was rebuilt as well and a new fuel pump was installed. All components replaced during the rebuild were stock short of the pistons as they aren’t available anymore and we installed a high volume oil pump. Any ideas? Currently the plates on the primary side are totally closed and it still won’t idle down. I had to turn the idle screws in about 3/4 turn to get it down to 700 but won't always sit there. I know the float is adjusted correctly. Also the airhorn gasket seems to always be wet with gas...not sure if that is normal.
Thanks.
After rebuild the car doesn’t feel like it has quite the same performance although I haven’t ran it hard due to break in period. Also it will not idle very well my biggest concer..some times 1000 or 700(ideal) or 1200 also when not at operating temp will die when taken off of choke, previously car would still idle fine. Timing is dead on where it was before, I have plugged the intake vacuum line to verify no vacuum leaks…the compression is fine although about 10% higher than before. The carb was rebuilt as well and a new fuel pump was installed. All components replaced during the rebuild were stock short of the pistons as they aren’t available anymore and we installed a high volume oil pump. Any ideas? Currently the plates on the primary side are totally closed and it still won’t idle down. I had to turn the idle screws in about 3/4 turn to get it down to 700 but won't always sit there. I know the float is adjusted correctly. Also the airhorn gasket seems to always be wet with gas...not sure if that is normal.Thanks.
Race Director
Joined: May 2006
Posts: 18,692
Likes: 2,572
I'm assuming this is a quadrajet? Are the secondaries completely closed, the engine has to be getting air from somewhere if the primaries are totally closed? How do you know the float is adjusted correctly if the airhorn gasket is always wet, sounds high to me? Did you rebuild the carburetor and set the float?
Thread Starter
Advanced
Joined: Mar 2003
Posts: 98
Likes: 3
From: Oglesby Illinois
Yes i rebuilt it myself, i also rebuilt the carb on my 75 at the same time with no troubles. I am certain the float is good....not sure the needle and seat is closing all the way. So if it idles high would that indicate a gas leak or a air leak?
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
If you back out the idle speed screw (close the throttle plate) and it won't idle down you have a vacuum leak. Air has to be getting in somewhere. I had this problem and found it to be the carb base gasket did not cover completely. Easy fix.
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