IF you don't over-lean it, the 10% won't give you any problem,, this engine needs little break in.. I have mine for over a year and to this day has never dead-stick on me.. I'm using 5% Nitro w/18% Synth/Castor blend (I live at sea level.. Inidiana is not much higher, but at least is higher than 12 masl, at our field