I'm sure this question has been asked many times before but I haven't found an answer specific to this engine so please bear with me. I've got some bad rings and am going to rebuild the engine so I'm exploring the possibility of upgrading it to 15hp while I'm at it. I've been told the only difference between the mid 80's Honda 9.9hp and 15hp is a larger jet and warmer thermostat. Anyone have any thoughts on that? Even if it is the exact same displacement, it seems to me both the carb and exhaust would be larger and maybe even the cam? 
Does anyone have any first hand knowledge of this? If all I can gather are rumors then I'll just stick with the 10hp and avoid the hassle. . .
Thanks!
Does anyone have any first hand knowledge of this? If all I can gather are rumors then I'll just stick with the 10hp and avoid the hassle. . .
Thanks!