My dealer told me that if you do not allow for a good solid warm up period you can smoke you hyfax in a quarter mile.
These Yamahas are different than anything else I have ever ridden when it comes to hyfax, you need scratchers, an adequate warm up and throw some snow in before you take off.
When I am riding the trail I consistantly let off the throttle and see if I feel resistance; when I do, I stop and throw some snow on the track and usually with the heat on the hyfax it melts the snow and I am OK after that.
I have heard that the hyperfax works much better but even then you need to follow the right procedures.
Hope this helps.