Hello and welcome to Just Answer,
Check the oil level and see if the oil is overfull or if it smells like gasoline. If it does then the carburetor needle valve is likely leaking. The carburetor will need to be rebuilt. If the carburetor does not seem to be the problem, then check the valves adjustments. The valves are set at .003" on the intake and .005" on the exhaust. The piston needs to be at 1/4" past Top dead center of the compression stroke when you set the valves.