Butterfly Valve Sticking...dieseling... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

SCdigger · 06-05-2009, 02:06 PM

Hey guys,

Been a while since I've been on (like a few years!)...have been having some trouble with dieseling with my '72 C10...took off the air filter cover and noticed that the butterfly valve was about a 1/3 of the way open...gave it a little tap, and it shut...started messing with it a bit, and realized that the valve most often did not close all the way or seemed to be sticking...is this something that can be resolved with a little lubricant like WD40 or tighting the little spring...I'm not a mechanic, but it does seem like it should be a simple fix...but wanted to get some input before I tore anything up...thanks for any input in advance.

Getting ready to clean her up and take some new pics! Haven't taken any since the time of digital cameras....

Greg Toney

webfoot · 06-05-2009, 03:00 PM

WD40 is not a permanent lubricant, use some light oil or penetrating oil which will not evaporate.

68gmsee · 06-05-2009, 03:13 PM

Mine was gummy and I used carb cleaner to clean it out. Sprayed it while working it and it loosened up. If you have a flat spot, tightening the spring may help.

Re: dieseling. I used stp and chevron additives everytime I gassed up for a month before it finally stopped. Now I use it about one a month or so. If you fix that sticky butterfly valve, that will help.

Longhorn Man · 06-05-2009, 03:45 PM

you are looking at this backwards. The butterfly flapper deal is supposed to be OPEN when the engine is warmed up. It doesn't close untill the choke is set.
You need to look at your timing, your idle speed, vac leaks, fuel quality, and if all that checks out, then there;'s a chance that the heads are carbon'd up and need cleaned. You can do that with a glass of water. When the engine is running at high idle, slowly dribble the water into the carb. The water turns to steam in the heat and fire, and it blasts the carbon off the bottom of the head.
Don't let the scared guys who will cry "don't pour water in your motor man" scare you. This trick is as old as the internal combustion engine, and is used on a somewhat regular basis in smog testing shops.

06-05-2009, 02:06 PM	#1
SCdigger Registered User Join Date: Aug 2005 Location: Anderson, SC Posts: 12	Butterfly Valve Sticking...dieseling... Hey guys, Been a while since I've been on (like a few years!)...have been having some trouble with dieseling with my '72 C10...took off the air filter cover and noticed that the butterfly valve was about a 1/3 of the way open...gave it a little tap, and it shut...started messing with it a bit, and realized that the valve most often did not close all the way or seemed to be sticking...is this something that can be resolved with a little lubricant like WD40 or tighting the little spring...I'm not a mechanic, but it does seem like it should be a simple fix...but wanted to get some input before I tore anything up...thanks for any input in advance. Getting ready to clean her up and take some new pics! Haven't taken any since the time of digital cameras.... Greg Toney

06-05-2009, 03:00 PM	#2
webfoot Registered User Join Date: Nov 2007 Location: Hermiston, OR Posts: 947	Re: Butterfly Valve Sticking...dieseling... WD40 is not a permanent lubricant, use some light oil or penetrating oil which will not evaporate. __________________ *Running in place gets you nowhere fast.* -me 1968 GTO 4-spd covnvertible 1970 K-20 4-speed, factory AC. Last edited by webfoot; 06-05-2009 at 03:01 PM.

06-05-2009, 03:13 PM	#3
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Butterfly Valve Sticking...dieseling... Mine was gummy and I used carb cleaner to clean it out. Sprayed it while working it and it loosened up. If you have a flat spot, tightening the spring may help. Re: dieseling. I used stp and chevron additives everytime I gassed up for a month before it finally stopped. Now I use it about one a month or so. If you fix that sticky butterfly valve, that will help.

06-05-2009, 03:45 PM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Butterfly Valve Sticking...dieseling... you are looking at this backwards. The butterfly flapper deal is supposed to be OPEN when the engine is warmed up. It doesn't close untill the choke is set. You need to look at your timing, your idle speed, vac leaks, fuel quality, and if all that checks out, then there;'s a chance that the heads are carbon'd up and need cleaned. You can do that with a glass of water. When the engine is running at high idle, slowly dribble the water into the carb. The water turns to steam in the heat and fire, and it blasts the carbon off the bottom of the head. Don't let the scared guys who will cry "don't pour water in your motor man" scare you. This trick is as old as the internal combustion engine, and is used on a somewhat regular basis in smog testing shops.



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