Fs 85 loses power in the heat

Check with your local Craigslist I

Try Craigslist in your area

Take a look...

This may give you a little guidance?
also check here for all things Stihl...

Stihl Trimmer Throttle Outdoor Power Equipment

And this video...

And you may find this useful...

http://www.stihlusa.com/WebContent/CMSFileLibrary/instructionmanuals/FS80_85_Manual.pdf

The E-85 is 85% alcohol. That will destroy the seals on everything, if your vehicle is not manufactured for it! so unfortunately replacing all the seals, or going through the fuel system is really the only way to correct the problem

Check your coil pak

http://www.mediafire.com/view/9duor5dwblekisn
hope this helps

http://www.mediafire.com/view/yleara73l4w78xa
This is what you asked for

I will come back to you with the method for adjusting this.
If you set the power valve to open at a higher rpm or restrict the vavle from opening to its maximum then your problem will be solved.

If you do the latter though you will definately lose your power at high rpm.

Could be several things including a broken return spring. If you are not experienced with these springs please take it to a reputable shop to avoid any personal injury.