Scenario: Brand new .63 (old style with intergal regulator), F plug, PM 20/20, 13x6 APC, tank with nylon strapping tape, filters on both lines, fuel system consistently holds pressure. Engine will start without incident and run "ok", tach'd about 11K with current prop and there's approximately a 1/2 gal. of fuel through the engine at this point. Problem: engine intermittently quits; it will quit both at idle and partial/full throttle. When it does quit, it's immediate- as if you'd turned off the ignition. Indications: at approximately 1/3-1/2 throttle, engine seems to run erratically as if rich; when the feed line to the carb is squeezed to limit fuel flow, it seems to smooth out. The regulator was- from the factory- slightly proud of the body; I've incrementally tried screwing it "in" to limit fuel flow through the transition but this seems to have little, if any, effect. Thinking there was possibly dirt or crud in the regulator, I disassembled it but it seemed to be free of any foreign objects. The plug has been changed- out of desperation- and that didn't have any effect. Also, I've tried running it with the glow ignitor on vs. off but can't seem to discern any difference. Checked the valve clearances and they also appear to be good.

Last season I ran another .63 (late model with reg. on pushrods) without incident and never touched the needles after their initial adjustment. I try to be careful about my setup of engines and fuel systems and feel fairly confident of the integrity of the fuel system. This situation has me completely baffled (and pretty discouraged); I'm ready to take a hammer to the whole works but have managed to restrain myself (there's always tomorrow!).

Any thoughts?