Snowmobile Repair: carbs and cylinder, yamaha 700, best bet

Question
i have a 98 yamaha 700 vmax triple,
last season i didn't change the fuel or add stabile,so i drained the fuel and sprayed the carbs...i did not take them fully apart.
it starts and runs fine for 5 minutes and then it starts to back fire then it cuts to 2 heads and then eventually dies..it always the same head that quits "from sitting position the leftside head"
.....thanks for any help on this

Answer
Hello Chris,

   I think your best bet, is to atleast, take that cylinders carb off, and clean the inlet needle, and make sure the floats move freely. Going to denniskrk.com, and getting a rebuild kit/repair kit, would probably give you the best results. Also, try installing all new plugs, NGK has the proper ones listed here: http://www.ngksparkplugs.com/index2.asp?country=US&nav=a0000 Make sure your heads are torqued down. That symptom can be from a worn crank seal, too, but I doubt it. Hope this helps, got to get that sled going before the snow hits! Best of luck to you with the Yamaha, let me know if I can help at all. --Arcticatman