You say you were adding oil to the tank. Is this the gas tank, as in premix, or the oil tank.
If you were adding oil to the fuel tank, this is wrong. You should allways mix the fuel in a separate container and shake it up.
Disconnect the fuel line at the carb and make sure fuel flows freely. If it does, drain the tank and try new fuel mix.
If not, remove the petcock and clean it.