I have a Byron F16 with a Rossi 81. I have not been able to fly it yet because the engine will load up and die! I have ran Rossi for many years ( since 1980) in boats using as much as 70% Nitro and they have been great engines! The OS has a much better carb ( for Idel speeeds!). The rossi's carb is large for more power which hurts its low speed some. I would get the OS!