Cutaway, do you have some known good fuel for comparison, or is the gift fuel all you have to run in these motors? I'd try to get some fresh Powermaster GMA 10/29 at the LHS. If they don't have that (and most don't), get some Wildcat Premium Extra 10% nitro (18% total lube) and amplify it with castor oil to 28-29% total lube. To do this, put 4 oz of castor oil in a quart container and fill it with the Wildcat Premium Extra fuel. That'll give you 28.25% total lube, which is sufficient for the Fox. Try it and see how it compares. If that fixes the problem, you know what to do round file the bad fuel. If not, then at least try a fresh hot glow plug in the motor just to eliminate this variable.