smellthe2stroke

Wow I feel for your little guy..

I am familiar with belt /clutch maintenance on big  Yamahas.  

The You tubes i looked at mentioned :

1.  There are two (2) speed limiters on that machine...but i am sure you checked that

2. There is a "spark arrester" in exhaust that easily gets plugged.  That will limit power.

The dealer sould give some pointers.

BTW I have bought OEM parts off Amazon...Yeah they came in an official Yamaha parts wrapped container.  I have also bought OEM parts off EBAY...

If you are stuck with buying parts  go to the yamaha web site.  With your model number they will list parts WITH the yamaha part number.  So if you buy from Amazon or Ebay you can verify the correct OEM part with that number.

Good luck