Remove pony tank, clean and line with RedKote or similar compound. Then if it still won’t run without choke, drill out soft plug that lines up with the passage from below main jet to the hex plug holding in high speed metering well next to the cast iron carburetor Venturi. Caution is advised tightening the two bolts that hold carb bowl onto Venturi section. Also make sure the gasket between has the center bulls eye ring still intact before reassembly. Also best to remove the idle screw and long brass tube that goes all the way through from right side of carb to stick into the bowl through that center ring on the gasket. Put it back like it was but about 1 turn out from snug tight is a good starting point. That one is adjusting AIR, so backing it out leans the idle mixture. The main jet screw is vertical sticking out the top of the bowl and it is normal, out to richen, in to lean the high speed/load mixture.