First off ik you wanna try and use it for back country but if that includes any kind of steep or deep snow that sled is going to be a bitch! They were very heavy sleds with short tracks. getting it started is the easy part. If i were you i would wanna go for as much weight loss on the sled as possible and then maybe invest in a track extension. that being said ill give you a quick run down as to getting it running.
fisrt: Gas!! gas degrades after time so its important to clean the tank lines and most important the carbs. easy to do cheap and should be done every year.
second: please check spark plugs nothing makes a bad sled like dirty gas/carbs and fouled plugs.
If those two things dont get the sled goin check your electronics. such as the switches!!!!!!! yes they do go bad.
And If these few steps dont work for you to get it running there may be a bigger problem such as pistions and rings that would be a total rebbuild of the engine costing $$..
My freind bought a 03 prox 440 and we are in the middle of a total rebuild and restore cost him with sled 2000$ not bad but it came with jets from 0-120000 ft and weights
finally if this sled doesnt have an elevation kit and you wanna ride high alttitude get the damn kit!!!!! otherwise the sled is gunna go BOOM!!! i can gaurente.
If you have any questions PM me or post your Q's here please :) and have fun