2005 kawaski prairie 360 problem help?

i got a kawasaki prairie 360 i rode it for about 4 hours and parked it i went to go ride it again that nite and at a quarter throutle it loss power and started backfireing on me so i brought in the shop to work on it. i started with the carp i pulled it out cleaned and while apart i but a jet kit in it. i put it back together and it still did the same thing so i change the spark plug. still did the same thing. i empty all the gas out of the carp and the tank and put new in. it still didnt help if anyone has any more ideas it would be greatly helpfull