Need more details! i've got the same problem with my mach, i change the plugs and it runs great then fouls them a couple hours later and runs like yours. At the moment i'm thinking the guy who i just bought it from either put to big of jets in, but i'll find out tommorow when i tear it down.
A forum community dedicated to snowmobile owners and enthusiasts. Come join the discussion about performance, racing, troubleshooting, trails, maintenance, riding tips, modifications, classifieds, gear, and more!