Easiest and cheapest way would be to add shims to your primary sheave. I believe your model can handle 2mm worth of shims but you'll need to verify this. Also you should upgrade to a stronger spring. Shims cost around 10$ and a stronger spring threw the Epi website is like 30$. I started out with this route with excellent results for thousands of kms before sending my primary sheave to Coop45 for his custom machining process.
Mite be worth checking out www.grizzlycentral.com as that site has much more information on cvt mods to help run larger tires on Kodiak / Grizzly 450s
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