[native1]

Make sure plugs are clean. Carbon deposits can glow and cause run on. Also can check timing, and idle/air mixture on carb. Don't run it too fat on the mixture. I had the same problem and this helped me. But when its hot it will sometimes do it anyway. I am always ready to pop the clutch during shut down to stop the engine over run. I hear it is bad for the valve train to run on so try not to let it happen. Of course 100 octane always helps. Good luck.