Are you sure it's the 85? I guess different states have different blends? In my area E85 is ethanol blend and 87 is usually non-ethonal?

Yes, ethanol blends affect preformance, ethanol burns cooler and don't have the Btu of non-corn gas. So IMO anything without ethanol is better not to mention the lack of miosture in ethanol blended gases which over time if left in your trimmer during storage will eat up the rubber seals by deterioration.

I would use 91 just to be safe. Best without alcohol.

I've used 87 in my Echo trimmer for going on 10 years with no problems....

I used 87 in all my outdoor tools but one day, the shop asked what I use. When I told them 87, they said to switch to premium.

Apparently, it must be a better quality or something in California. Very little difference in cost but they said it will prevent many problems in the future.