Hey Orange,
I've got a '74 3/4 ton with a 350 where a 454 used to be. I got the truck with the 350 and headers already installed on it. I had to do 3 things to get rid of a complaint exactly like yours:
1. Put a heat shield on the frame between the header pipes and the fuel lines. I made it out of 18 ga. sheet steel and pot riveted it to the c-channel.
2. Make another shield for anyplace where the exhaust pipes are routed beneath an exposed fuel pipe. I've got dual tanks on mine, so I made more shields for the tank switch valve and the crossover pipe from the drivers side tank.
3. Put a new fuel pump on there. I've used numerous brands over the years, and the only ones I trust nowadays are NAPA and AC-Delco.
Those EPA-mandated 2-line systems work pretty good to keep fuel in the pipe from overheating and vapor locking. The idea is to recirculate excess gas back into the tank so what is in the line doesn't get too hot. Leave it there and functioning.
The only things left to check, if you haven't already, are the rubber lines at the tank and anywhere else on the truck. If there are any cracks on the outside, replace them. Of course if you are going to the trouble of dropping your fuel tank to check them, then replace them regardless.
Hope this helps, as I fought those symptoms for a couple of YEARS before I got it licked. Yeah, I know, "years" is a long time, but I'm like the cobbler with the shoeless kids...
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David
newbie #4153
