What is your altitude in TX? The altitude and rich mixture would account for the differance in power. In fact the rich mixture alone would. Any engine turning a prop over 10,000 at a full four cycle is doing very good indeed. Most C/L engines turn 8 to 9,000 at a full four cycle and burst to 1,000 to 2,000 RPM higher when breaking into a two cycle. Though they are set up to turn larger props at slower speeds than most R/C engines.