You can kill it by touching a gloved finger or a stick or whatever against the flywheel while it's idleing. That way it doesn't run out of fuel and lean out. Be sure to move the piston to bottom dead center while the engine cools between tanks. If it's top dead center it may stick there because of the pinch area. let it cool completely between tanks. If it's hard to get it to turn over try heating the head with a heat gun or hair dryer. That will make the sleeve expand a little and let it turn over easier.