What determines my overall engine rpm at WOT?

typically my machine used to run at 8500 rpm +- at WOT

my last couple rides Ive seen ~9k RPMs +- at WOT

the machine shifts fine and backshifts with no issues, Ive had the motor in and out a couple times in the last couple years clutch center to center distance was set-up with a Yam tool along with intial offset

Is it my belt thats causing the RPM increase ? it measures in spec width wise but I didnt check it for circumference, it sits correctly on the secondary clutch when its not moving ...any ideas ?

If you didn't do any clutch work it sounds like the belt is glazed and slipping causing your RPM to go up. Prep your belt and test. Also did you change your belt a hard vs soft compound with also change rpm. To control WOT RPM is mostly done with weights in the primary clucth. If you want to go from 8K to 7K you would add weight or take away weight to gain rpm also you can control rpm and belt grip with were the weight is either heel, middle or tip. Primary spring can also be used but most like is setup for engagment after you determine where your sled runs at. Clutching is like a black art there are many ways to get the same results and and most poeple have differnt ways of doing it. Then theres the secondary setup and that's a whole topic in itself

I didnt do any clutch work.

Thanks for the info re weights, the engagement rpm is good You may be right about slipping I did get some funny oscillations at 5-7000 rpms on my last ride. I just thought it was the conditions (loose powder on icey base) but may have been belt slipping. I didnt think of that so i didnt check the clutches for temperture

I know just enough about clutching to know I need someone who knows more about it than me

what do you use to prep your belt ?

Ill check the circumference this weekend too...it may just be time for a new belt even tho visually this one is in good shape

There are a few ways to clean your belt the best way for me is I use green scotch brite dish pads to scrub around the sides of the belt to get any glazing off you can also use sandpaper or streel brush. Then with a cloth and a small amount with my finger I wipe it down with acetone also the acetone is used to clean the clutch sheaves it does a great job of removing all the black blet scuffs with are caused by slipping and heat.
After you ride the clutches should be warn, but if you can't touch it then there is a issues.

What belt are you running?

the 383 doo belt is GARBAGE. And does exactly what you described after a few hundred clicks....