According to the guys at Sta-bil, ethanol attracts water which in-turn can cause acids to form. Sta-bil supposedly fixes the ethanol problem. All I know is that my weedeater brand engines run like crap on E-10. This season I'm using fuel with no ethanol (or at least there was no indication on the fuel pump that the gas had any ethanol in it) and some Sta-bil. I ran my FX26SC tonight and it ran great, the leaf blower had some old fuel but is starting to sound better because I added some of the new fuel.