The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Truck has started running rich & terrible MPG

rich weyand · 09-24-2016, 10:00 PM

At 65, 5000 rpms? Sounds like you were in second gear.

Which would be the case if the vacuum line from the back of the carb down to the transmission broke. The tranny thinks you are at WOT.

And the carb is struggling to add enough gas to keep up with the vacuum leak.

I'd start with the vacuum line to the tranny. Inspect it where it connects to the vacuum modulator on the transmission, and all the way back. Replace the rubber portion on general principles.

09-24-2016, 10:00 PM	#2
rich weyand Registered User Join Date: Apr 2014 Location: Bloomington Indiana Posts: 1,041	Re: Truck has started running rich & terrible MPG At 65, 5000 rpms? Sounds like you were in second gear. Which would be the case if the vacuum line from the back of the carb down to the transmission broke. The tranny thinks you are at WOT. And the carb is struggling to add enough gas to keep up with the vacuum leak. I'd start with the vacuum line to the tranny. Inspect it where it connects to the vacuum modulator on the transmission, and all the way back. Replace the rubber portion on general principles. __________________ Rich Weyand 1978 K10 RCSB DD.