The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Seems like I have to keep advancing my timing

rich weyand · 08-10-2016, 03:36 AM

I keep thinking about your problem. It could also be a vacuum leak. One thing you could try is disconnecting the brake booster and transmission lines and blocking the ports on the carb, just for testing at idle. If it clears up the problem, you have a leak in a line, or a bad brake booster or transmission vacuum modulator.

The reason I say a vacuum leak is it will leak air into the manifold, making the mixture leaner, which slows the burn, which will want more advance.

08-10-2016, 03:36 AM	#22
rich weyand Registered User Join Date: Apr 2014 Location: Bloomington Indiana Posts: 1,041	Re: Seems like I have to keep advancing my timing I keep thinking about your problem. It could also be a vacuum leak. One thing you could try is disconnecting the brake booster and transmission lines and blocking the ports on the carb, just for testing at idle. If it clears up the problem, you have a leak in a line, or a bad brake booster or transmission vacuum modulator. The reason I say a vacuum leak is it will leak air into the manifold, making the mixture leaner, which slows the burn, which will want more advance. __________________ Rich Weyand 1978 K10 RCSB DD.