So, you assume that there is not any reasoning behind delivering the Yamaha this way, eh? Could it in fact be that Yamaha want's less scrutiny over it's entire product line for EPA compliance? Could it be that they all ready know that delivering a YZ motor with a few changes is much easier for us to modify to competitive status than re-designing the whole motor, making it very expensive to meet red-sticker performance?
Nah, that couldn't be it.
My 450X took years to figure out how to get it to run fast and stay torquey. My WR took about three hours.
I would be MUCH more concerned about suspension. It took Yamaha years to catch up there......