What do you think about using this oil, Exxon Elite. I use it in my plane which is counter piston and air cooled. I know that these engines get alot hotter than our bike.
Aviation oils like Aeroshell, Phillips, Exxon Elite, etc. are designed specifically for use in aircraft engines. These engines usually operate under continuous RPM operation, alot like your air cooled lawn mower once the engine is started it is operated within a narrow power band. Unlike automotive or motorcycle oils which operate under a broad range of power settings. I do use aeroshell 15w50 in my John Deere mower and have no problems but once the motor is started it runs at a continous RPM until I'm finished mowing. Just like your airplane, once you are in flight the RPM range is rather narrow until you are preparing to land. Your car and motorcycle engines vary from idle speed at stoplights to high speed (RPM) on the highways. Aviation engine oils are really not going to save you any $$$ either as they cost about the same as a synthetic and If I'm not mistaken are mostly semisynthetic. Also, You might want to be sure of approval ratings as it could become an issue if warranty claims get involved.