My brother has the Magnum 61 four stroke which is very similar (identical?) to the ASP. It spins a 12x6 prop at approximately 10,500 rpm using fuel with 15% nitromethane. My brother's engine was terrible until it had a gallon of fuel through it. Poor idle, poor transition, etc. He actually considered throwing it in the trash. Now it will idle "forever" and transitions well after prolonged idling.