I have your exact sled except I have changed it in so many ways to try and make it perfect for me. (Shocks,A Arms,seat,Xhandlebars,skiis and bling) I bought Bill Cudney's clutch kit for the 600 sdi. The first thing I noticed was the gas mileage dropped a little. My motor is rebuilt and now pulls his kit at the rpm's desired, using his included directions. It took the annoying dead spot from the sled and made it SO much more fun to drive. The only complaint is the massive back shift! After running it for a season or two I have grown to love it as the power is always there but when others ride it they never like it. It will almost slow the sled faster than applying the brakes. As a matter of fact if I apply the brakes when riding very hard and let them off , the kit slows the sled more even after I release the lever. You learn to ride with the throttle on at all times until you actually want to come to a stop, hence the gas mileage drop. It still however gets better mileage than any other sled I have ever rode with so it isn't drastic. Performance wise, I found that dropping the top tooth in the chain case made it perfect. At a grass drag in the summer, I was forced to move up to 600 improved, because of my reeds, but right off the trail, with not other changes, it produced a time 4 tenths faster than any other 600 in the 600 amateur class. So 500ft performance is improved with the Cudney kit. Top speed never really changed, but with the new top gear and clutch kit it gets over 100 on the speedo very easily and quickly.
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