Please make sure the fuel you use in your O.S. Max .40 LA contains castor oil in the lubrication. It's a plain-bearing engine that will benefit greatly from castor oil in the fuel.

As far as RPM is concerned, we use a 10 x 6 propeller and expect to see the engine turn in the mid-11,000's. Idle should be about 2,500-2,700 RPM.