You should not be running pump fuel (mixed with alcohol), but if you can get 93 octane non-ethanol blended fuel from the pump, then it will be fine with a 12:1 piston. My CRF250 is 12.9:1 stock compression and calls for 93 octane - I found out that at 94.5 octane the engine suffers a loss of power. I have been running 91 octane non ethanol recreational gas and have no problems with either spark knock or detonation.