Pretty old thread, would be nice if he responds.

But if you take the cover off and both sheaves are moving up all the way then it is probably the wet clutch. Not sure if the manual has testing procedures or not for the wet clutch, or centrifugal clutch is what I think the manual calls them.

 

The original poster did say what cured it in subsequent posts. Do what he did and try it, before thinking about the centrifugal, that involves going into the oily bits.