Engine - Drivetrain

Try without first.   If it acts like it's running lean get a programmer.   I did one on my wife's 09 DCT Rancher.  I put a Weisco programmer on with the top end, but I honestly think it would have run fine without it.   Didn't make much of a difference at all over the stock 420 cylinder.  Not worth doing unless your original 420 cylinder is gone too far to be bored oversize again.   I was curious as to the 520 top end, but you have to either turn down the outside of the bottom of the cylinder (Reduction Boss sells those ready to bolt on) or grind the cases a little to clear the bigger jug.    I've gotten away from 420's and am sticking with the older machines, so never got around to the 520 swap.    

Thanks guys! Got it fixed up. 

Alright I'm gonna give it a try and see what she runs like. Hopefully alls well. I will send my scope down to check the piston just to see at some point

Ive done it with a kit from a Kentucky dealer. No issues with the machine after doing it.  Fi model. Its really 475cc vs the 420.

I like the way they look. I need some too for a forman ,but don't want to pay the high price. I'll probably make some . Is that some type of rubber or plastic?