Your Diagnostic Wisdom Please - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bluec10 · 07-30-2014, 07:26 PM

I'm frustrated with trying to troubleshoot a problem with my truck.

My '69 has a 250 with a three speed manual. Its a low mileage truck and I enjoy driving a truck with the powertrain of the trucks we drove when I was a kid.'

So...I rebuilt the factory carb two years ago and it made a big difference. The truck also has a new fuel pump and a new alternator. Up until the end of last summer the truck was running great. Smooth acceleration, lots of power, and it cruised right along at highway speeds.

The problem started suddenly. The truck would accelerate relatively well to about 45 or 50 mph then start stumbling. It was like the truck wasn't getting enough fuel. The funny thing was that after sitting for a few minutes I could restart the truck and it would run better...for a while..

I checked and blew out the fuel filter. I sent some compressed air through the fuel lines to make sure there wasn't a blockage. Since that time I've run some Sea Foam through the system and refilled the tank with fresh gas.

Any ideas? I'm baffled - especially since it went from running like a top to its present state almost overnight.

07-30-2014, 07:26 PM	#1
bluec10 Registered User Join Date: Apr 2002 Location: Manitoba, Canada Posts: 663	Your Diagnostic Wisdom Please I'm frustrated with trying to troubleshoot a problem with my truck. My '69 has a 250 with a three speed manual. Its a low mileage truck and I enjoy driving a truck with the powertrain of the trucks we drove when I was a kid.' So...I rebuilt the factory carb two years ago and it made a big difference. The truck also has a new fuel pump and a new alternator. Up until the end of last summer the truck was running great. Smooth acceleration, lots of power, and it cruised right along at highway speeds. The problem started suddenly. The truck would accelerate relatively well to about 45 or 50 mph then start stumbling. It was like the truck wasn't getting enough fuel. The funny thing was that after sitting for a few minutes I could restart the truck and it would run better...for a while.. I checked and blew out the fuel filter. I sent some compressed air through the fuel lines to make sure there wasn't a blockage. Since that time I've run some Sea Foam through the system and refilled the tank with fresh gas. Any ideas? I'm baffled - especially since it went from running like a top to its present state almost overnight. __________________ Present: 2015 Tacoma. Yeah, not a GM, but I love it. 1969 GMC 32,000 - fix, drive, relax, fix... 2019 BMW R1250 GSA - Yahoooooooo 1979 Honda GL 1000 - retro touring at its best. Past: '05 Sierra 4x4 - Had 270,000 KM and running well when it was written-off by a stop sign runner. '94 F-150 from the "F word" company. I'll admit it...good truck. Sold what was left of it for $800 to a guy who came to pick it up at 11:00 PM with cash in hand. Hmm. '79 Sierra Grande (Black) organ donor - perfect rebuildable 4-bolt 350 and a good TH350. '76 Sierra Grande (Orange) - hate isn't too strong a word. Kid who bought it turned it into a hot rod. '68 C-10 R.I.P. - Dad's old truck...too far gone to resurrect. '59 C-50 - with hoist. Truck is gone, wife isn't. Nuff said.



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