remove the inbound line to the pump and see whats doin there. if its stinky old gas, or barely any comes out, etc., its ungood.
there is metal fuel line mostly except there are rubber pieces at the fuel sender and entrance exit going thru the frame. change all these rubber pieces out with new FI rated rubber fuel line from vatozone. the mechanical FP is a puller it creates negative pressure to draw fuel. this will collapse rubber fuel hoses if they are old. this will also pull air if there is a pinhole along the length, so again no fuel draw. lastly, vacuum = vapor lock (but you are not there yet).
you can unhook the line at the sending unit and at the FP and blow air thru if you have a compressor. but just change out all the rubber lines for sure.
I elected to install a mr gasket electric FP back by the tank / rear wheel area and ditched the mechanical FP with a blockoff plate. elec pump is a pusher not a puller, so there is no vacuum - we now have positive pressure. it also helps prevent vapor lock in heat, as pressure = higher boiling points same as a radiator. worked great. wire in a rollover switch or oil pressure switch to shut off the pump in case you rectum.
on my new motor I did put a mechanical FP back on, and left the elec pump as well. the main risk here is if the mech. FP gives up and I push fuel into the block... but we are at like 4 psi so..
lastly - psi. priming your carb = no don't do that. you just need fuel flow. generally speaking a carb expects 5psi-ish of fuel pressure. for a very short test, put a gascan on the roof of the car or hang it on the fence etc, and run a tube down to the carb. it has to be a few feet high so we get enough pressure from gravity. 1psi = 1foot IIRC (?)
have a fire extinguisher in case deficate interacts the rotational device.
if you have a bunch of hands, on the inbound line on the FP put your finger over the hole and crank the motor see if it has any suction.
that's all I got.
- saylor