Use the method all the old Sun machines had painted across the top in big letters- - - - - -"We test, not guess!"
Do a pressure, volume, and vacuum test on the fuel pump. There should be 3-5 pounds of fuel pressure at the inlet fitting of the carburetor, 10 inches of vacuum or more on the suction side of the pump, and both pressure and vacuum should hold for a few seconds after the engine stops. The pump should deliver at least a pint of fuel to a catch container in 30 seconds at idle speed. Failing any one of these three tests is a good reason to replace the pump. If the pump tests good, you've most likely got an air leak between the tank and the pump, or there's a restriction inside the tank.
Jerry
