May need to get one of those ignition replacement kits so you can advance the timing.
Changing every o-ring & gasket in carb to alcohol resistant ones
Alcohol has a higher compression ratio than gas so a higher compression piston would be a big help along with jetting changes
Also E85 will wash lubrication off the engine's cylinder walls, So find a motorcycle oil compatible with E85 & that has a good acid neutralizer. (Ethanol is slightly acidic)