Tom,
I think with those outboard floats and being farther away from the cylinder heads, the Holleys don't have the same issues with boiling fuel that the Webers do (all the innards being so close to the heat source).
Since I have a mechanical pump, it's off when the engine is. I have watched the pressure rise slowly after everything is shut down, so it's pretty clear what is happening.
Spacers aren't the answer, since the clearance with the hood is already pretty tight. So I guess I'll have to put in the return line to the tank or get used to wiping down the base of the manifold with degreaser every few days.
