Theres a chance your fuel pump is not working correctly. A good running fuel pump should push about 6-7 psi. So if it is old it could be down pretty low.

Also your rubber lines could be allowing the pump to suck air, and thus reducing available psi. Besure to check the fuel tank rubber lines too.

I would try the fuel lines first since they are cheap, and do get old. I like to use feul injection line since it is thicker and more abrasion resistant.