FS 80 petrol/2 stroke Stihl grass trimmerr which doesnt turn? ?

I recently cleaned the magneto field magnets removed some string that had fouled up on the shaft and replaced the sparkplug on my Stihl trimmer . When I put it together again, the motor started beautifully but the cutter at the bottom of the shaft doesnt rotate (turn).If I rotate the cutter shaft turns up to cup but not with motor. There doesnt seem to be physical connection between shaft and motor is it a magnetic coupling? if so perhaps the gap betwwen field magnets and magneto wrong?