#1 is there fuel in the tank
#2 is the fuel in the "on" or "reserve" position
#3 if so, does fuel flow freely out of the fuel hose
if not, you need to clean the petcock, if it does, move on to the carb
have you tried fresh fuel? fresh plug? does pulling the choke help? also you should do a leakdown test to make sure that you aren't needing to add that fuel (spraying the gas in) due to an air leak.