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- - Im stumped!! (https://67-72chevytrucks.com/vboard/showthread.php?t=470874)

I have a 70 GMC pickup with a factory 396. I have had problems with them fuel delivery since i bought it and i have been trying to figure it out. I think it is vapor lock cause when it starts up cold it runs great but slowly leans way out. it never dies but starts to pop and cough like it is running out of gas. i installed a clear filter to watch and see what it it does. Its doing what i expected the filter starts out full then little by little about 20 minutes time the thing is bone dry. I replaced the fuel pump and also wrapped the line from the pump to the carb with insulation. the truck has headers and the fuel line runs down the frame but the line looks like its not too close to the header. do you think i could have a oven effect with the header and the frame. im lost i dont know the deal is. the truck has three tanks and it does the the same thing on all the tanks. the truck has a edelbrock carb on it do you think that could have anything to do with it.

Re: Im stumped!!

I had a similar problem with my '72 402 BB. I finally traced it to a collapsing fuel line under the cab where the the tank feeds the fuel line. The short rubber line is there to allow the cab to flex w/o damaging the fixed steel line as it runs along the frame to the fuel pump. For that matter, you may want check or change both of them. #1 at the tank under the cab, and #2 under the engine where the line feeds the fuel pump. Hope this helps.....

Re: Im stumped!!

Is your gas cap vented? Have you tried running it with the cap off?

Re: Im stumped!!

Quote:

Originally Posted by Clutch442 (Post 4748980)

Is your gas cap vented? Have you tried running it with the cap off?

^:agree: Sounds like textbook gas cap problem. A vacuum builds up in the tank and it quits letting fuel out.

Re: Im stumped!!

I did run it with the cap off no change in the problem.

Re: Im stumped!!

Im going to try a new gas cap and see what it does. I ran it with the cap off at idle but didnt drive it around with a load on the motor so im going to try and get a whole new cap. the one I have is a old locking cap and the rubber around the rim is all cracked and dried out.