Colorado Parks and Wildlife advises that you run all of that old stale fuel through your snowmobile at the start of the season. Don’t do it!
Drain that crummy fuel. Dispose of it; maybe have a nice bonfire. Then fill your tank with nice, fresh, clean fuel.
Pull off your air cleaner, give your carb a good spray with carb cleaner, and put it back together. Crank up your sled with that nice, fresh fuel, make sure it runs right and go have a nice ride!