I have a Stihl FS-85 weed trimmer. It stalls out on full throttle. Runs great with the choke a little open, stalls when I open the choke all the way and squeeze the trigger, even with the air filter off, the spark arrestor is clean, the fuel filter is clean, spark plug is good. Gas mix is fresh. It's a 1999 and has been runnig great all these years. You could clear cut forest with the damn thing when it's on the pipe. I've been running the same pre-mix in it as I have my KX500. Phillips race 100 octane unleaded with castor oil. I'm thinking it's not getting enough fuel with the choke full open at full throttle. I blew the fuel lines out. Only likes to run and idle with the choke cracked a little. I think it's starving for fuel at WFO. What do you think??? Thank you for your thoughts.