I have a Flymo 330 Compact which constantly cuts out during operation. At first I thought it was the cutting box becoming full, but every time this occurs the box is at most a quarter full......this is becoming very irritating as it now takes ages to cut my lawn!!
it's usually the microswitch which is operated by closing the grass box lid. Flymo have had several goes at designing this and they all seem to give trouble. Check that the grass box lid is making the switch turn on when you close it.
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