could be that the pump arm is worn if it's not a new pump, or the cam lobe that runs it might be worn if the cam wasn't replaced, or the gasket you used to mount the pump is too thick, or there's some sludge plugging the tank pickup or a rubber line before the pump is rotten inside and collapsing .... could start by disconnecting the line from the tank, replace it with a rubber hose into a gas can and see if that fixes it
Bill
