Just installed a new carburetor, fuel lines, regulator, Holley blue pump, filters before pump and at carburetor inlet. Pressure set at 7.5 psi per carb builder's recommendation. My problem is the pressure drops to about 3.5 psi after driving a few miles. The pump is mounted not quite as low as the bottom of the tank so is this really the issue? It doesn't really seem to be a venting issue. I'm gonna pull the tank and check for an obstruction in the pickup, sending unit assembly. Anyone out there running an in-tank pump and a carbureted engine? I'd really like to get rid of the electric frame mounted pump.

 

I guess I have a couple questions to ask, what size motor and what size fuel line are you running?
My motor is a 496 and run 5.5 psi with no issues, maybe try lowering the psi?
I ran the blue pump/ regulator with my 396 and a #6AN fuel line and didn't have any issues with my pressure being set a 6psi when I raced my car.
I can't tell from you picture, but is your fuel line close to the exhaust? If so, insulate the fuel line to keep the heat away from the gas.