Question: 

Hello, your instructions included in the 91CR engine mention 

4.RUNNING-IN

      b) Plane -Fix engine on plane or test bench with propeller, run engine at low rpm at least 30 minutes??

      How low rpm, 2000,5000,8000? I don't know what low rpm is to you. Please give use a approximate number.

      For a 10 lb. airplane what size propeller do you recommend using for this break-in, 11x8, maybe?

Answer:

Thank you for contacting Novarossi and we appreciate your purchase of the Novarossi 91CR engine.  Low RPM is around 2 - 3,000 RPMs. The 30 minutes of bench time running fairly rich is sufficient.  The engine should be ready to fly. Just keep it on the slightly rich side for the first few flights. However make sure the engine is set to peak out so you have plenty of power to fly. 

The 11x 8 is a good prop for flying fast. We would suggest 12 or 13" props for normal flying. 3D flyers who fly slow and need rapid transition use 14x4 Xoar props. But the engine is very prop friendly. Use the prop that provides the performance you want on the specific airplane. The engine will handle it OK. 

The main concern to engine life is too lean runs when the engine actually sags due to a lack of fuel. The fuel in 2 cycle engine provides the lubrication and cooling needed so lean runs can damage the engine. However, other than this caution which is the same for any two cycle engine, it will handle a wide variety of props. Experiment. 

Thanks again for contacting Novarossi.