Just bought a 2008 450 grizzly.
Wicked!
love it!
only real gripe is the clutch engages and disengages at too high revs.
especially going downhill. . the clutch lets go much too soon compared to my old 300 kingquad.
so far not found anything about adjustment etc
Theres stuff about shims and clutch kits, in some detail.
but what problem shims etc solve?

 

On Yam Grizzlys the clutch is a centrifugal type like most quads. There is a one way clutch for the overrun in the centrifugal clutch which may have failed. The variator system can have faults but there is a lot of guesswork and wrong info on the net, few know what they are talking about. I'm fairly sure the Grizzly variator belt is engaged with the pulleys all the time so won't disengage at all unless the belt is slipping.