A J, I never knew you replied till today.
once I got the plane to the field and ran it a 2nd time the RPM came up another 300 to 12.500 peaked, and 11,900 tuned for flight (APC 11x8). I still think I can lean it a click or 2 more. I will keep it checked by the plug. the better pilots at the field say she does 100 mph LOL
and with that big Heli carb the engine runs and idles beautifully with a prop.

if you click on my link below you will see the stock OS 50sx is the same engine, same liner and same piston, but a smaller plane carb of course, the review says the SX with the smaller plane carb and stock muffler turns the APC 11x8 at 11.000 peaked (5% nitro), so I am 900 over that

BTW, once this 15% is gone I have 3 gallons of 30% Heli fuel

OS Max 50SX

Jim