1968 L71 427/435 Idle

I sent the carbs for my 68 L71 to Holley to undergo their remanufacturing process. The carbs returned to me like new and I highly recommend their service.

My mechanic installed and tuned the carbs to the manufacturer’s specification. The car starts on the first turn of the key and settles into a nice 1250 to 1500 idle while cold with the kick up set. As the car warms the kick up disengages and the idle settles down to about 900 to 1000 RPM. However, when the car attains full operating temp (185º to 200º F) the idle raises to between 1500 and 2000 RPM.

Are there any suggestions as to why this occurs and what can be done to keep a reasonable idle?

Thanks

If those butterfly in the carb don't close & it's hard to see on the car you'll get a high idle. Had this problem with my speed demon & couldn't see it until I took it off & looked close at the bottom of the carb. My linkage was bent just enough to keep them open a hair. I also agree it could be a vacuum leak. Check your vacuum. I would guess that engine should read 12-15lb at idle & I would go to the lower end first. Also make sure the hoses on your carbs are hooked up properly.

Alan

Thanks gentlemen, I appreciate the insight. I took the car out this morning, ran it until hot and looked at the linkage. As usual it settled into a 1950 to 2000 RPM idle. I backed the idle screw down until it no longer touched the throttle return. The throttle stop now rests directly against the throttle body casting containing the idle adjustment screw. It’s beginning to look like something is bent. I plan to do a vacuum check this weekend.