[2muchbluE]

Are the bearings in the back seated in the correct position...not in the "slipping" stages on the ramps?

Did you measure the stack to be within spec?
Is the clutch boss completely seated?

Those have been my 3 mistakes.

 

[2muchbluE]

1:33 it is not a yamaha but the bearings sit at the bottom of the small "ramps"
That is the best way I can explain it.....
double check..... then make sure clutch boss is seated completely.
If it is not any of those.... my last guess is the stack height......