Thanks Kenneth. Am hoping the additional air, hot plug, and smaller prop will get this motor out of the doldrums. A local buddy seems pretty sure that that should do the trick. I know that these old Foxes are being run successfully on 10% nitro fuel on Yankee Nippers, Coyotes, and other S/L combat planes, so mine should work as well. I've read rather vague descriptions of "unreliable" performance on the Mk 3 with restrictor installed. Apparently, Fox changed the restrictor on the Mk 4 and subsequent version to keep the slow combat guys happy -- must have been a reason, but I haven't been able to get details on what the problem was. My engine has the restrictor epoxied in, so I'm guessing it leaked air pretty badly. It may work much better with a suction setup, but that's not something I'm willing to go to yet on a combat plane. One of the joys of a pressure fuel system, when it works, is rock steady rpm regardless of attitude.