Don't know if this helps but I had a similar problem that was driving me crazy for weeks.
I discovered that my gas tank - fuel pump fuel lines were rotted just enough to allow some gas to flow to the pump, but not enough for reliable delivery. It seems that RUST was the only thing holding the line together bbecause when I had a good look at the lines tthey looked like swiss cheese.
What you can do to eliminate delivery to the carb and the pump is to run a hose from a portable gas can connected directly to the fuel pump (disconnect the line to the tank). If it is getting good delivery then you can isolate your problem to either the gas tank or the line. Just be careful with the open can of gas and have a fire extinguisher handy, just in case.
