Just tried the fox stunt plug on my fox 50th ann. .35 today. I have tried everything to get this engine to run right, including the wooden plug, varying tank height, uniflow, clunk, pressure, standard vent, etc. NOTHING made a difference. On a hard outside the engine would burp and die about 75% of the time. I have had the motor on 3 different profiles, all the same problem. The engine is now in a rsm ringmaster. Put in the stunt plug and the problem is fixed. Not kind of better, but truly fixed. The engine sound changes when going into a hard outside, but it is not a burp. THANK YOU FOX! I dont have to switch engines to get a reliable pattern run. Having said that, its probably just a hot idle bar plug, but whatever - it works.