Kawasaki Prairie 700 Frustration

Okay..I have about had it with my 2004 Prairie 700.  Every winter it starts to run like *((&*&...and I end up taking it in to the dealer and have it gone through which costs about $150 each time.

Well..here we go again..It runs fine in the summer..but as soon as the weather turned cold, it's backfiring, rough running, refusing to idle, and seems to have about 1/2 of its usual power.  The motor sounds muffled if that makes scence...not throaty and strong like normal.

Any suggestions to keep this from happening?  Taking it to the dealer every year is getting to be damn expensive.  And of course they will not give any suggestions..they just shrug the shoulders and laugh.

Anyone else have this problem with this model?  I purchased this machine brand new, it's stored inside, I change the oil regularly, I put in quality FRESH gas, I don't mess with the motor,  and I dont beat on it or run it through mud/water. 

It is blowing regular colored white exhaust.  I pulled the aircleaner and that is good.  I keep it clean and free from rodents as I ride it every day around my ranch.

Any suggestions before I haul it to the dealer and trade it in on a Honda? !