# Stihl FS-85



## arcas (Nov 14, 2004)

Hi. I recently bought a used FS-85 brushcutter and I've noticed that the idle speed seems to gradually increase the longer the engine runs. Around the house I can do the trimming in 30 minutes or less so this increase is barely noticible. But I just took the trimmer down to my parents' farm to help clear out some fence rows and after a couple hours of use, I noticed that the engine's idle speed was noticibly higher and in fact the clutch was slightly engaging causing the head to slowly spin. I'd guess 100RPM or so.

Is this a symptom of a problem? Oviously, I could reduce the idle speed so that the clutch no longer engages but I'm afraid if I do that then the engine will have difficulty idling when cold. I admit I haven't actually done this yet since I didn't have a screwdriver with me in the field and I'd have to let the engine run for a long time here at the house in order to test it (I'm sure my neighbors would love that).

Thanks for any info.


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## T-Trim (Nov 5, 2004)

I think it's because the saw is small with good amount of mass to it plus that engine is pretty warm up by that time.
I have a echo brushcutter and it does the same thing 

Tony
:roll:


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## bugman (Aug 12, 2004)

when metal gets hot it will expand letting a little more air and fuel in. nothing to worry about its natural with alluminum


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## arcas (Nov 14, 2004)

Thanks for the quick responses. I guess I should have realized this was simply due to the metal expanding but seeing how this guy appears to have been abused by the previous owner, I wasn't sure.

Thanks again.


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## bugman (Aug 12, 2004)

well its well built


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