My rock solid dependable YS140L stopped in flight two weeks ago. On disassembly, couldn't help but notice the failed connecting rod, damage to the aluminum piston near the wrist pin, the piston ring (came out in pieces) and the piston sleeve was scored. Replaced all these with new parts after thoroughly cleaning crankcase internals. Re-assemble with leak proof gaskets. Engine started immediately and operation back to normal, or so I thought.....

Engine starts right up when cold and produces full power (16 X 10 APC @ 9,200 rpm @ 85 deg. F, 100 ft. above sea level) at full throttle. The problem is, when engine warms, it loses power. Then, it's hard to start up. When it starts, it surges, then clears but only achieves partial power at full throttle, yet idles normal @ 2,200 rpm. When hot, it won't start at all. I'm running Cool Power 25% with added syn oil. YS 4 Glow plug okay. Check valve okay. Inline fuel filter free and clear. Compression very good. Best its been since I've owned it. No internal header or muffler obstructions. Disassembled regulator. Diaphragm, plunger, plastic end cap, spring, o-ring all okay. Disassembled head to check the valves, springs, seats, etc. Cleaned the valves and lapped in with jewelers rouge. Haven't run the thing since confirming regulator internals and the valves were okay. Waiting for the weekend. Gotta work and it gets dark early now.

Guys, have I overlooked something? Could it be a setting problem? Any recommondations besides sending it off to Gardnerville?

Steve