Fuel problems

[DET45]

A friend and myself own a 1978 and 1979 chevy pickups. His P/U has a fresh 350 and mine has a fresh 454. Both of our trucks seems to lose fuel out of the fuel line when our trucks get to operating temperture. When we first start up our trucks our glass fuel filters fill up with gas and the trucks run fine. However after they warm up the filters start to drain and my fuel pressure gage drops to zero. Truck still runs but goes flat when driving. I have changed fuel pumps three times to include electric pump, edelbrock mech pump, and factory pump, I even used the electric and mechanical pump together and yet the fuel problem still exists. I also changed three different carburetors. After that I dropped the fuel tank and checked out thr fuel sending unit and for any obstructions (none) So I replaced all of the fuel line, still losing fuel. After that I ran the fuel line in a gas can to eliminate the trucks gas tank (still loses fuel) I checked for vacume leaks on the intake and other areas (ok?) My gas tank has one fuel supply line and one vent line, both are new and un-obstructed. I could be wrong but it looks like the fuel is being pushed out and down the fuel line from the carburetor. The reason why I say this is because I have my fuel system set up starting with the carb, then the glass fuel filter, then the fuel pressure gage, pump, then gas tank. What happens is after the truck reachs operating temperture you can see the glass fuel filter (located approx 6 inchs from carb) starting to drain then after that the fuel pressure gage (down stream from fuel filter) starts to drop to zero. That tells me that the fuel is being pushed out and down the fuel line I think? Anyway I am totally confused and don't know what else I can do. My friends 79 P/U is doing the same thing and we are both are scratching our heads. PLEASE HELP......Thank You....

[79BIG10]

Welcome to the board. When gasoline overheats and boils inside the carburetor bowl or fuel pump of a hot engine, it ceases to flow. This can cause stalling or hard starting. This is called vapor lock, and it usually happens during hot weather. If a hot engine won't start, all you can do is let it sit and cool off. You should check the cooling system to see if anything is causing the engine to run unusually hot (a bad thermostat or cooling fan, for example). Switching brands of gasoline may also help.

Being in Texas I know that it gets hot here. I've only had that happen to me once before.

[magnethead]

yea, its common in nascar, but it shouldn't be vapor locking right after warm-up, i should take quite a while. What's the gauge reading and is it stock mech fan or aftermarket electric?

[79BIG10]

But if the filter or the hose is ran next to the block or an exhaust manifold then it's going to run hotter and cause that. Also if you have steel lines on the fuel pump to the carb they also absorb alot of heat.

[DET45]

Thank you all for your replys, My truck always runs cool and the fuel filter and fuel gage are not located next to the engine block. Fuel line is three eights rubber flex line. My truck has a new four row radiator and clutch fan. Clutch on fan is new and rated for the 454 BBC. This problem occurs after the truck reachs operating temperture (around 180 degrees). I am totally confused on this one my friends.......DET45

[79BIG10]

It might be in the carb then. You could add a spacer which would help performance slightly but also might fix the problem.