Stuck throttle? I would imagine its congealed oil on the barrel. Two option, take the carb off and heat it a bit melt the crap, or sometimes saoking it raw fuel will help. Since it is stuck open, just putting some fuel in the venturi and letting it soak down around the barrel is not going to work. If you have a micro torch, you could probably do it still on the plane. Heck, even a heat gun would do the trick if its fuel.