My 2001 -700MXZ done the same.I took it to the dealer for correction and they told me there was no problems concerning the carbs.It was quite a bit harder on gas and oil than my 2000 mxz 700.I heard also that this was a common problem with the 800's and the dealer said the 700 had no complaints,so I suggested I had an 800 in my MXZ 700 or I was the first to complain.The dealer did nothing but set the oil pump to talke a little less oil.This did not help,but my brother in law and I looked at it and found the lever on the carbs not returning all the way.
When it is warm and idling high ,you can either hit the throttle lever quickly a time or two and it will idle or reach down at lever on the carbs and you can see it is sticking.I believe the spring on the lever is too light ,but be cautious because if you strengthen the spring it will be stiffer on the thumb.The best fix I came up with was I sold it and bought a new Rev. 800HO.
