Good sled you have there!
I've done several years of testing on these 3X3 to know that that motor can put out serious hp!!
Unstead of repeating myself on xcr set-ups, I have found a good link that can help you get the most out of your sled!
I have run these sleds for long enough to know that this guy's set-up is pretty good - except I don't agree with some of his choices of parts.
First off, I have tried this set-up (actually, I think it's based on an article from snowtech 1996)
Don't use the carbon tech reeds with the Frett brother spacers. I mean it works, but you will be much hapier with the boyesen reeds with stock boots. (cheaper, runs crisper, and makes it easier to remove the airbox)
I don't think you want to simply "geardown" on top. Next years XCR's came with better gearing, but still not perfect. I like to use a 22 top and a 40 bottom (good for 1000' runs). Gets the ratio to 1.81. I also like to keep a 23 top handy for 2000' runs
You can use the clutching in the link, or just keep the stock 97/98 setup. I use a round wire Polaris almond with 54 grams weight. This set-up is best used on the 23/40 ratio, but it's pretty close for the 22/40. These motors run good at 7800-8300 RPM.
You will need to get a CDI from a 97/98 - trust me, best money ever spent. Run 29 deg BTDC with 97/98 cdi. Box will auto-shift you to 13 BTDC at 6000 RPM
Last but not least, TEMPA FLOW II. Most important performance mod for this sled.
jetting for me is 45 pilots, (air screw 2-3/4 turns)
Stock needle from a 97/98
Stock needle jet from a 97/98
Keep the jetting 340-360-360 with the tempa flow
I run a DG triple pack silencer on mine - throttle responce is incredible.
BUT i keep 360-380-380 mains with the tempa flow on this set-up.
Keep the front shock tight. get as much power to the ground as you can. If you find it pushes too much in corners pull in your limiter straps.
KEEP THE CARBS SYNC'd. and belt deflection right on. These motors don't really like to be run under 4600 RPM.
Don't get bent up on the idle drop after an extended stop, it's built like that... Timing retards to throw more heat into the pipe and lowers engine stress. If you want more details on that perticular subject email me.