Idle surges momentarily - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Asshat · 01-13-2022, 06:42 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.

LT7A · 01-13-2022, 08:04 PM

Quote:

Originally Posted by Asshat

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.

I'm sorry I don't have a guess for you, and there are plenty of smart guys in the general discussion, but you might get more feedback more quickly if you post this in the section of trucks that cover the year that the engine was made.

**Steeveedee** · 01-13-2022, 10:29 PM

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.

geezer#99 · 01-14-2022, 01:10 AM

Or it could be sticky weights in the distributor.

Asshat · 01-14-2022, 01:18 AM

Quote:

Originally Posted by geezer#99

Or it could be sticky weights in the distributor.

Distributor is new, only be ex n on the truck for about six months. And really low miles.

blazer2007 · 01-14-2022, 10:07 AM

unfortunately new doesn,t mean much these days

**Palf70Step** · 01-14-2022, 10:55 AM

I also tend to think might be something in carb. Maybe dirt of buildup, some bad gas. Maybe try running some sea foam down the carb and see if it works something loose.

geezer#99 · 01-14-2022, 11:26 AM

Do you have any idea what your idle rpm is when hot?

Asshat · 01-14-2022, 12:41 PM

Quote:

Originally Posted by geezer#99

Do you have any idea what your idle rpm is when hot?

Probably about 800.

geezer#99 · 01-14-2022, 12:44 PM

Turn it down.
Should idle at 600 easily.
Likely at 800 the mechanical advance is just starting to add timing which increases rpm.

01-13-2022, 06:42 PM	#1
Asshat Registered User Join Date: Jul 2015 Location: South Orange County CA Posts: 1,259	Idle surges momentarily 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, 10:29 PM	#3
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,088	Re: Idle surges momentarily 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. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

01-14-2022, 01:10 AM	#4
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,512	Re: Idle surges momentarily Or it could be sticky weights in the distributor.

01-14-2022, 10:07 AM	#6
blazer2007 Registered User Join Date: Jan 2007 Location: vernon b.c. Posts: 3,022	Re: Idle surges momentarily unfortunately new doesn,t mean much these days

01-14-2022, 10:55 AM	#7
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 46,634	Re: Idle surges momentarily I also tend to think might be something in carb. Maybe dirt of buildup, some bad gas. Maybe try running some sea foam down the carb and see if it works something loose. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

01-14-2022, 11:26 AM	#8
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,512	Re: Idle surges momentarily Do you have any idea what your idle rpm is when hot?

01-14-2022, 12:44 PM	#10
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,512	Re: Idle surges momentarily Turn it down. Should idle at 600 easily. Likely at 800 the mechanical advance is just starting to add timing which increases rpm.



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