What Stump said, check for a vapor lock (heat) prob then plumb the pump inlet to a can of gas to elim or confirm a prob from there rearward (line dia too small/pinhole in line/pickup and sock restriction) then what is left is pump/line capacity up front. I like to T at the carb inlet & run it to a reg & then to a return line to the tank & use the reg to modulate the amt of return flow to the tank to control the psi and to keep a constant flow of fuel