Idle surging, up and down… - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Asshat · 01-13-2022, 08:50 PM

More often than not, the idle will move up and down a bit when I restart the truck after it has been warmed up and driven. Then, after about a minute or two, it goes away. It’s a straight six, 292, carbureted. It just started doing this recently.
Could it have something to do with the fuel pickup in the tank?
Vacuum leak - if so, why would it go away? Vacuum leaks don’t fix themselves.

val1gonzales · 01-13-2022, 08:57 PM

Could be the choke. Not sure if its vacuum operated or manual. If vacuum operated could be normal due to temperature changes from off to start. If you had a vacuum leak you'd most often get a little backfire pop, hissing from leaking line or a high idle. Try locking down choke lever and see if it still has the same problem.

Asshat · 01-13-2022, 09:12 PM

Quote:

Originally Posted by val1gonzales

Could be the choke. Not sure if its vacuum operated or manual. If vacuum operated could be normal due to temperature changes from off to start. If you had a vacuum leak you'd most often get a little backfire pop, hissing from leaking line or a high idle. Try locking down choke lever and see if it still has the same problem.

Choke is mechanical, and pretty sure it’s not moving.

**Steeveedee** · 01-13-2022, 10:50 PM

I replied in General Discussion, moments ago.

Not a vacuum leak. It sounds like it may be spilling a little fuel out of the bowl when parked, and after the engine is running awhile, it clears up. I don't like blaming carburetors for anything, but in this case it may be a suspect since it runs OK the rest of the time.

To add, here- do you run it far enough that the tail pipe turns something other than dark gray? It could be that the float is just a bit too high and it runs OK except for when parked some fuel spills over.

01-13-2022, 08:50 PM	#1
Asshat Registered User Join Date: Jul 2015 Location: South Orange County CA Posts: 1,265	Idle surging, up and down… More often than not, the idle will move up and down a bit when I restart the truck after it has been warmed up and driven. Then, after about a minute or two, it goes away. It’s a straight six, 292, carbureted. It just started doing this recently. Could it have something to do with the fuel pickup in the tank? Vacuum leak - if so, why would it go away? Vacuum leaks don’t fix themselves. __________________ 1963 C20, small window, long bed 292, 4-speed

01-13-2022, 08:57 PM	#2
val1gonzales Registered User Join Date: Apr 2019 Location: San Antonio Posts: 124	Re: Idle surging, up and down… Could be the choke. Not sure if its vacuum operated or manual. If vacuum operated could be normal due to temperature changes from off to start. If you had a vacuum leak you'd most often get a little backfire pop, hissing from leaking line or a high idle. Try locking down choke lever and see if it still has the same problem.

01-13-2022, 10:50 PM	#4
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,692	Re: Idle surging, up and down… I replied in General Discussion, moments ago. Not a vacuum leak. It sounds like it may be spilling a little fuel out of the bowl when parked, and after the engine is running awhile, it clears up. I don't like blaming carburetors for anything, but in this case it may be a suspect since it runs OK the rest of the time. To add, here- do you run it far enough that the tail pipe turns something other than dark gray? It could be that the float is just a bit too high and it runs OK except for when parked some fuel spills over. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA



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