RV Repair: onan genset 4000 fuel pump, screw gun, gun battery

Question
I am having trouble getting my generator to start. Everything appears to be working and have traced it to a dry gas line. When I siphoned the gas line I could start the generator but it went dead after the gas in the line was used up. I originally thought it might be the fuel pump, but that wouldn't explain the generator running when I siphoned fresh gas into the line. Is there a way to test the pump to confirm? If it isn't the pump is there another explanation for the gas line to dry up?

Answer
yes you can take the fuel line off where it goes to the carburetor and take a cordless screw gun battery and jump it to see if it will pull fuel.
it could be a weak fuel pump the only run about 2 to 3 psi so if its gotten weak it could only be pulling about 1 psi