You're going to have to "dig in" to the fuel tank to find out what is going on in there. You have a problem with the suction hose and or baffles in the fuel tank. A missing or damaged suction hose can cause these symptoms. Drain ALL of the fuel, remove the fuel pump, wipe out the fuel tank, and inspect carefully the suction hose and baffles. Replace any deteriorated or missing parts. Be careful when reinstalling the fuel pump and boot, if you don't install correctly and turn it you can kink the suction hose. Some of us have installed a spring inside the suction hose to prevent it from kinking or collapsing. David Teitelbaum vin 10757