We figured out the over heating problem it was mud in the fins of the radiator now after about 1/2 hour it will shut off but will restart right away and run good then shuts off again but will always start right up it does not overheat so take a guess what this might be. The atv ran great when we bought it from the dealer, this all started when we road it in the mud. Thank you,

 

Maybe try draining all the fluid in the radiator and putting new fresh fluid in? Sounds like your radiator isnt working. Do you have a warranty? The first day I got mine and took it for a ride my radiator fan stopped working. The dealer told me a sensor fried, they got the part and fixed it.