# Stihl FS91 problems running



## AmateurSawer (Oct 20, 2020)

Bought a new FS91 a few years ago to trim the lawn and,with a tri arc or saw blade,rose briars,small rush and cedars.
I'd used it some but not much.I was liking the way the three sided blade cut tall grass and weeds and didn't wrap up.
Loaned it to a neighbor to cut a path through some high weeds. I know,bad idea, but the guy is very mechanical minded and runs his equipment like he should.
Started to use it this year and wouldn't start.I noticed the fuel didn't look good so dumped it,rinsed the tank and carb with WD40,changed fuel filter and air filter and tried again without any success.
I sent it in to my dealer to be fixed.They got it running after saying it seemed to be frozen up and the fuel tank smelled like some kind of spray pesticide.They soaked some parts and reassembled.Got it running and it was picked up.I started cleaning up some high grass with it and hit apiece of metal.Killed the engine and no restart.Dealer said I may have sheared a flywheel key.Got it back again last week.
Today,I was cutting a path for electric fence though high dead grass and multiflora rose.Didn't seem to be accelerating high enough but I just figured it was because it had been a while since I heard it run.It would idle down and run fine at idle then come back up without hesitation.Suddenly,it just stopped.No getting it to restart no matter what I tried.
I left it sitting for several hours and tried starting from cold start.No starting.
Pulled the plug.It was lightly coated a dark brown .cleaned with wire brush and tried again.Still nothing.I would have tried a new plug but didn't have one here that size.Book calls for Bosch USR 7AC but there was an R 10 in it.Don't know i dealer had substituted it or not.
I need to call and talk with the mechanic about what he found and did.One problem is a different mechanic worked on it the last time so he doesn't know the whole story.

Any ideas or experience would be helpful. If it was a few years older,it would get tossed but I doubt it's run 25 hours total and is a 350 dollar machine.Not like it's a box store homeowner model,either.


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