I recently acquired an O.S. 70 Surpass which starts O.K., but will not reach peak RPM (above 8,000 with 12.5x8 prop). Also after it runs for a minute or 2, will quit running. It can be restarted in a minute or so, but the trouble repeats. Have checked the valves and set the mixture screw to factory setting. Bearings seem O.K. in that the engine turns smoothly and quiet. Compression seems good.

Suspect possible cylinder liner and/or piston problem, but I have not disassembled the engine.

Any comments/suggestions appreciated.

Thanks,

DaveB