I have an OS 46fx that doesn`t want to shut down, even when I`ve gone to idle and pulled the trim all the way down ( air intake appears fully closed ). It will rather slowly shut down and kill, but not like my other engines which shut down quickly. No problems in flight with it, however. Could this be an air leak ? Other possible causes? I suppose this is a better problem than having one that doesn`t want to run at all !!