Please get yourself an inductive tachometer. Guessing at it doesn't cut it. Plain and simple.
These trimmer idles at 2800 with clutch disengaging before reaching this lower rpm.
Plus these engines are tuned at 3100-3200 max idle speed. First warm up the engine for at least one minute then you tune L to best speed and then set LA @ 3200 rpm. You may need reset LA a few times while finding L best speed @ 3200 rpm. Then you enrich L until you drop to 2800 rpm. If the trimmer head is still turning when you are at 2800 then you have clutch problems.
And there can be a problem with the carburetor but first you got to try to tune it to the above specs as you got to remove the a possible setup problem.
As far as rebuilding it cost nearly as much as a new carburetor from since both has to be obtained from Stihl if you want a OEM kit or carburetor.
I got the new carb on and it does run better.
Checked out the clutch, and as you mentioned, the other problem was in the clutch. After removing the housing, and disconnected it from the shaft, one little turn of the bolt that holds the clutch to the fly wheel, the clutch sprung back into place. So removed the clutch, wire wheeled all the rusty spots, reassembled and at first, the head didn't turn. After I gave it throttle, it spun the head, but never released it after I let go of the throttle.
Took the housing off again, and just barely loosened one bolt, and it snapped back into place.
So there's something about tightening it down, that makes it stick out.
Weak spring? Or a bad washer? worn spacer?
Wait i think i figured it out. It's the bushings, right?