Thanks for your help, Troy. Good to hear from you. This YS63S (regulator up front) has over two gals. run through it. 12 X 7 APC, tachs @ 12,000 rpm, full power on the ground. After reading your thread, it appears the problem I'm experiencing may be heat related. After all, it's been a long HOT summer in Central Florida. The engine is hard mounted inverted and is surrounded by a narrow fiberglass cowling with large hole in front for the cylinder assembly and regulator to protrude through. There's another hole (half-dollar sized) in the bottom for access to the glow plug, etc. and small hole in the side for the high end needle and idle mixture screw. I've always been told the head of the regulator screw should be flush (or close to it) with the body sidewall. At present, it's turned clockwise (three turns from flush) to lean. The idle mixture screw has been turned clockwise to enrichen to compensate.

One last question, when advancing the throttle from idle to full power after allowing the tank to pressurize, the engine bogs down. Is this an indication of a lean condition or a rich condition. The YS manual that comes with all non-fuel injected engines provides instructions on adjusting the regulator to compensate for lean/rich conditions but it seems to take a trained ear (not mine) to conclude whether the transition is lean or rich.

Steve Homenda