I have an old '77 B200 van with a 360. When I first got the van everything was totally stock, and it suffered from a very bad vapor-lock problem.

To cure the problem (and add a little power), I swapped in a Holley 600 carb, Edelbrock RPM Air-Gap intake, Mallory 140 GPM electric pump and return-style pressure regulator, and plumbed the system with -6an inlet line and -8an return line.

The regulator (with gauge) makes pressure adjustsments easy, but I have noticed that the set pressure drops from 7psi cold, to around 3 psi after the engine is fully warmed (185 degrees). The pressure change also changes the float level which screws-up the fuel mixture.

Any ideas what might be causing the pressure changes?

 

Are the new lines in the same general location as the old ones? Have you wrapped them in some sort of heat shield material?

Just going out on limb here, thinking that maybe you compensated somewhat for the vapor-lock problem by adding the better fuel management system but if the lines are in the same place, maybe the heat is still affecting the pressure.

Eric