I was going to suggest that it was a blown motor. My buddy had the exact same issue with that sled. We thought it was electrical but ended up blown. You should be able to get it bored, new pistons and rings (assuming it's not too bad) for under $300. Find a machine shop to do the bore (usually $30-50 per cylinder), then order the pistons/rings/gaskets (pistons/rings for about $100, gasket kit for about $50) on ebay. That's a solid sled, albeit older, and is worth a $200-300 fix.
I know of a great shop in Princeton, MN that does good bore work for cheap.