Help!! Can't figure this out!!!

[Seatown-gmc]

I have a 70 gmc with factory 396/402 big block. The truck runs fine at start up and when it gets up to running temp it starts to run out of gas! I put a new fuel pump on(mechanical) and also blew the line out back up threw the tank so I know the line is clear also rebuilt the carb. I have clear fuel filter on it so i can see what the fuel is doing. When I shut the truck off and the motor cools the fuel comes back. The truck does have two saddle tanks but I don't use them. The truck has headers to. I'm lost any advice?
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[Andy4639]

Just a thought. Next time when you crank it let it run then shut it off when it starts doing it. Then crack the gas cap and see if it's pulling vacum on it. U should here it sucking air into the tank. If so get a vented gas cap are check the vent line for being clogged.

[Seatown-gmc]

Cool ill try that! Thanks for the reply!
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[custom1970]

Maybe a piece of trash in your fuel tank? Should be a screen but it could have come off.
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[Andy4639]

Let us know what u find out.

[Secret Squirrel]

Not sure this applies but,

I had the same symptoms in my 72 olds 442 after replacing old pump, turns out it was vapor locking. Next time it starts to act up touch the fuel pump to see if it is hotter than normal.

I had a clear plastic fuel filter in the line near the carb when the engine got to operating temp there was no more gas.

I tried to get a spacer to get the pump off the block, ended up going with a electric.

[rsmarr1982]

is the fuel line from the tank ran inside the frame rail? my buddy put a 402 in a 73-87 body style truck that originally came with a small block and the fuel line would vapor lock when the engine warmed up. the 73-87 big block trucks have the fuel line ran on the outside of the frame rail. the "C" of the frame holds the heat.

[Seatown-gmc]

I did pour water down the line from the filter to the pump when it was running and the fuel seemed to come back. The pump could be getting hot. Is that normal with a factory set up?
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[Seatown-gmc]

The fuel line runs down the inside of the frame rail.
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[rsmarr1982]

ive never had a factory 67-72 big block im not sure how the line is ran from the factory . headers do add extra heat. if the fuel line is ran inside the frame rail by the engine id reroute it to the outside to see if that fixes it.

[Secret Squirrel]

Originally Posted by Seatown-gmc

I did pour water down the line from the filter to the pump when it was running and the fuel seemed to come back. The pump could be getting hot. Is that normal with a factory set up?
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Mine did, I did not even run headers. Maybe some new pumps are not insulated enough?

[CC69Rat]

An old hot rodder's trick is to clip two wooden clothes pins on various places of the fuel line from the pump to the carb. It will cause the heat to dissipate off the line.. if this makes it better, I'm thinking vapor lock too.

Do you have an Edelbrock carb?

[knomadd]

Originally Posted by Seatown-gmc

I did pour water down the line from the filter to the pump when it was running and the fuel seemed to come back. The pump could be getting hot. Is that normal with a factory set up?
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If this worked, then it is vapor lock. Cooling the line keeps the fuel from vaporizing due to heat. Check the routing of the fuel line and make sure it is not touching any part of your block, intake, or exhaust. If it's within an inch of the block, try to route it differently so it isn't so close to a heat source. Until you move the line away from the heat, you'll be chasing vapor lock.

If your line isn't close to a heat source, then your pump is running too hot causing the vapor lock. Either try a different brand or go electric.

[haminator]

LOL I had a flat plastic bread tie in my tank once. The sock was long gone and after about a 2-5 miles of driving it would suck right to end of the pick up. Just thought I'd share. On another note I have heard the Edelbrock carbs are bad about cooking the fuel with out a thick carb gasket.

[ole dollor]

there could be something inside the tank that sucks up to the fuel line, i have seen this before...i also have fixed several by putting a three line fuel pump on and running the small return line back to the top of the tank and installing a fitting on the tank so the fuel keeps moving and has time to cool off, this works very good with the old carter afb...that is now the edelbrock , they can't stand any dirt,and flood real easy when pressure goes up...i have done this to the q-jet with much success ....hope this helps.

[1970 C10 MJW]

another fix would be if the pump is the problem getting to much heat, wrap your headers with the high temp header wrap found at most of your car parts stores, i did this to my 70 and i love it, engine runs so much cooler, and i gained HP and the engine bay is much quieter, i used the bran DEI good stuff