To determine the jetting, you have to pull the carbs and remove the bowls. Take the jets out and read what's stamped on them. You want to jet for the lower elevations. Yes, the temp dropping with elevation increasing works in your favor to keep it from getting "too rich". But, if you jet for the higher elevations / lower temps, you're going to burn the motor down at the lower elevations.
If you have fresh oil in the chaincase, check the adjustment on the tensioner. Put the rear end up in the air, remove the drive belt, loosen the jam nut on the tensioner, and unscrew the tensioner a couple of turns. Screw the tensioner back in by hand as far as you can, spin the track or secondary a little in each direction as you continue to snug the tensioner. Loosen the tensioner 1/4 turn, hold in place, and tighten the jam nut.
Put the new belt on, warm it up with some gentle riding for a few minutes (similar to how you would warm it up when you head off for a ride and the sled is cold), then check the offset and deflection.
The "proper" way to sync the carbs is with a sync tool. However, since the only reason that the vacuum that they develop would really be different is if there was an air leak, you can do it totally without a sync tool. In fact, doing it without the tool actually makes it more likely for you to identify a difference of conditions between the cylinders.
Syncing the carbs:
- You need to adjust the free play in the throttle so that there is about 2-3mm of play. This is necessary for the safety switches to function properly.
- With the kill switch engaged and the key off, zip tie the throttle wide open (or have a buddy hold it).
- Remove the airbox so that you can easily see and access the intake side of the carbs.
- Ensure that the slide is installed correctly with the cable inserted correctly into it.
- Ensure that the slide cap is screwed on all the way.
- Ensure that the top edge of the carb slide is -just- above the bottom edge of the carb intake throat. If it is not, adjust the cable on the slide cap until it is.
- Repeat for each carb.
- Remove the zip tie / release the throttle lever.
- Rest the solid part of the drill bit in the carb opening "the long way" and adjust the idle screw until the slide -just- comes in contact with the bit. This will give you a reasonable starting point for the idle.
- Once all of the carbs have been adjusted, slowly squeeze the throttle and ensure that all of the slides begin to move at exactly the same time and go up exactly the same amount.
- Adjust the air screws according to the manufacturer's setting.
Now, adjust the choke plungers.
- Get a thin gauge piece of solid wire and bend it at a 90 degree angle about 1" from the end
- Remove the airbox so you can easily access the intake side of the carbs
- Apply the choke
- Slip the bent section of wire into the enrichment hole on one carb and release the choke - make sure that you can not easily pull the wire out
- If the wire comes out easily, you need to screw the plunger adjuster into the carb body until you feel it contacting the wire and keeping it from moving
- Screw the adjuster in another half turn from that point and tighten the jam nut
- If the wire does NOT come out easily, pull on the choke lever until you feel tension in the cable - you should only have to move the handle a small amount after you feel tension before you can remove the wire
- If, after lightly applying the choke, you still can't remove the wire, you will need to unscrew the plunger adjuster from carb body
- Unscrew it until, with the choke off, you are able to remove the wire then use the process above to adjust it correctly
- Re-install the airbox
You're now ready to start the sled and tweak the air screw and idle settings until it's where it needs to be.