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Check to see if the thermostat is opening and closing faster you go the more snow kicks up and you get better cooling

Check the coil and connections if the coil and connections check okay then it is probably the stator if it is the stator check out rm stator web site

If your belt is worn it won't allow you to get max rpm, also if you have stock jetting the main jets may be too fat (rich).

Sounds like it's running rich, I don't have much experience with this type of sled but that's what it sounds like.

Check and clean the points. You might have to gap them, open them up with a tiny screwdriver, being careful, and spray contact cleaner, then just rub a rag lightly through them. Gapping is usually...

I am looking for a shop manual for a 2004 mxz renegade 800, hopefully free.