Have you replaced the pump diaphragm in the carb? It's NAPA Echlin 2-4218 or Hygrade C203-5 and can make a world of a difference. If you do take the carb apart, beware of the little "BB" like check valve that often falls out. Although I think the diaphragm can be replaced without removing the carb but I don't remember right off hand. It's been awhile since I've done it, probably because the new ones can handle the modern gasoline whereas the original ones couldn't.