There are two generic causes that might produce your symptoms. The first is that the engine is running on pure petrol rather than 2-stroke fuel, and consequently it keeps seizing up then releasing as it cools off. If that is happening, the outside of the piston is likely to show signs of distress. Hence Joe's initial question. The second generic cause is that the engine is cutting out rather than seizing, which would probably be due to either temporarily lean mixture, or an intermittent ignition fault. It would be a bad idea to assume the second generic cause and try to find an engine fault, if it is really the first generic cause: every attempt to start the engine without oil in the fuel would do additional damage to the piston, rings and bore. Hence Joe (as always) has given excellent advice. The first thing you need to do is eliminate the possibility that the first generic cause applies, by inspecting the outside of the piston.
