Here in Brazil, the E85 is 85% ethanol / 15% water. the water acts as additive, raising and keeping heat of combustion. I think that little engines doesn´t like that water at all.

If your engines are runnig good, the answer is the gas in your E85.

And there is another problem, our gasoline have 23% of E85.

I will do some try with ethanol at 98% and castor oil.

good flying out there.