The 1947 - Present Chevrolet & GMC Truck Message Board Network

The 1947 - Present Chevrolet & GMC Truck Message Board Network (https://67-72chevytrucks.com/vboard/index.php)
-   Engine & Drivetrain (https://67-72chevytrucks.com/vboard/forumdisplay.php?f=24)
-   -   Idle issue (https://67-72chevytrucks.com/vboard/showthread.php?t=810132)

dave`12 08-04-2020 03:34 PM

Idle issue
 
I have an issue that I can't seem to figure out.

I put a Holly Demon carb onto the truck a while back. Since then, I've had the problem that the idle is high until I juke the throttle. I'm pretty sure the problem came with the new carb. But the carb has been on quite sometime just sitting in the garage (about a year) as I was not driving the vehicle. Now I'm recently retired and using it more, so time to address the issue.

Specifically: Truck idles around (I'm guessing 2k, no tach) when I start it up. If I juke the throttle, it will come down to what sounds right. This happens every time I drive the truck hot and cold. So each time I come to a stoplight, I have to juke the throttle for a normal idle. I played with the choke, lean and rich to no avail. I've pulled the throttle linkage (from under the hood) frontwise (which would lower the idle), and it does not move, so I don't think a stiffer idle return spring would help. I sprayed carb cleaner around, but did not find a vacuum leak.

I find it baffling that each time I juke the throttle, it goes down, but won't on it's own.

Truck runs great. Good power, smooth off idle, etc.

By the way, I have aftermarket a/c that works good; and when the a/c is on, the idle seems to do the same thing.

1967 c10. 350cid Holly Street Demon 625 electric choke.

Any help appreciated!

geezer#99 08-04-2020 05:05 PM

Re: Idle issue
 
Check the side to side movement of the primary throttle shaft.
If it moves much the throttle plates will hang up on the bore and change your idle.
You might need to pull the carb and check from the bottom.

dave`12 08-05-2020 07:21 PM

Re: Idle issue
 
Thank you geezer. I took off the air cleaner and duplicated the conditions, light throttle, and noticed that under light throttle, the choke would partially close. Then, with a "juke" it would open back up.

I disabled the choke and the issue went away.

I live in Florida, so not a big deal, but I would prefer it worked properly.

Any ideas?

thanx

geezer#99 08-05-2020 07:39 PM

Re: Idle issue
 
Lean the choke setting slightly.
Most electric chokes you just rotate the black cap. Should be some existing marks on it for reference.

The Rocknrod 08-07-2020 10:15 AM

Re: Idle issue
 
Quote:

Originally Posted by geezer#99 (Post 8787648)
Lean the choke setting slightly.
Most electric chokes you just rotate the black cap. Should be some existing marks on it for reference.

That's right. The instructions show what to do.


All times are GMT -4. The time now is 05:28 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, vBulletin Solutions Inc.
Copyright 1997-2020 67-72chevytrucks.com