Sounds like foreign material in the carburator, or a leaking filler valve. Pull the needle valve all the way out, leave the fuel line connected and blow through the vent line. Fuel should come out of the needle housing, but not through the filler valve. Then put the needle valve back in, but only a couple of turns, and do the same again to force fuel through the spray bar. Fuel should flow into the carburator throat. Turn the needle valve back in to the normal setting and take the glow plug out. Now spin the engine with the starter for 5 seconds to eject the excess fuel that ran into the carb while you were doing this. Put the plug back in and the engine will start.

Jim