When it revs high and will not shut off, check the plug, wet or dry. Is the slide bottoming out all the way? Get an aftermarket kill switch also. When you clean the carb, that means removal of all the jets, remove all the tarnish and actually poke something through to clean it, do not scratch the inside. And do the same to all the passages. I think if its an airleak, it would not idle correctly, it would rev high and erratic. You will need to replace the float valve and seat if it comes out. Racing it gets replaced yearly, otherwise, when you have jetting/carb issues, replace it and save a headache!