honestly, 200rpm is splitting hairs in my opinion, I would ride the sled first in snow and see if its something your tending to "think" is a problem or something that has a definite problem in the operation of the sled. When you shim that w/w/w spring its going to also affect the overall shift out. The softer shift out is what makes you use that w/w/w spring in the first place, thats the gain, it loads the engine faster then a y/w/y spring does and shifts quicker. The springs 45kg start is the same as most of the other good yamaha springs for the long cover, so just changing that wont gain you anything.They(other springs from yamaha) will engage at the same speed because they are the same 45kg start. youd have to use a aftermarket spring with a 50kg start to get it higher. The higher the engagement on snow, the less traction you get, 3900-4000 isnt high, just saying when you progress going higher what happens.
By shimming that w/w/w spring youll more then likely just be at almost the next spring which is a y/w/y spring, (45kg/128kg), or dang close which is a slower upshift,more rpm upshift. Your engagement will be higher but the shift wont be the same as intended, thats your choice.
I also would double check the roller size in the front clutch as if someone installed or used 15mm rollers not only does it lower the engagement but also the shift rpm, so then youll be looking to see why your low on peak rpm as well. It should have 15.6mm rollers in it.
I have never had a problem with the set up, this is why i pointed out the first things that came to my mind on the belt,rollers,etc, theres usually a cause behind why something doesnt work as planned in a set up.
check them rollers if you get the chance. hope this helps.
