Diggs, If you are talking about the nelson that I sold you....that engine has 1 run for 45 seconds on it that I ran,,,asside from whatever dave put on it when he rebuilt it,,,and I agree. I know of an engine at the nats that only turned 17200 on the ground, and was one of the fastest engines in the air, so ground RPM means NOTHING!..
Prop it and run it.