Are the blades well lubricated? also can you spot any damage on them ? are the blades pinched to tightly? if the machine runs, when you rev it does it sound like it is under load? if i is then i would suggest it was one of the above. if it sounds like it is reving up fine then i would say to look at the rotary gears that the blades attach too. if they are all fine (not damaged or worn) take a look at the clutch. i had a similar problem and the pivots on the clutch shoes were rusted and prvented them from moving out . a bit of sanding and dab of grease will do the trick.
Jamie, April 2010