Paul, as noted, I have experienced no undue problems with Fox engines, thus I am not the best source for solving problems. Again if you could be more specific in describing the nature of your difficulties it would be easier to assist. Also you might try http://www.flitelinesolutions.com/. These fellows seem to know all about Fox engines. I would only add that I use fuels with a fair amount of castor in my Foxes, and thus used I believe they are among the most durable model engines made. (Let me quallify that- I ain't tried 'em all, but when I have I'll let you know).

jess