I would pull the top off the carb, and check that rubber diaphragm for tears Next I would pull off the float bowl, and look for dirt/anything up in the main jet.
Also pull off the vacuum line that goes to the fuel petcock. Suck on the end of the line, and you should have a steady stream of fuel out of the tank.
Could be as simple as a bad spark plug but I think the above stuff may get it.