MYSON HAS A YAHAMA 400,EITHER '02 OR'03, GRIZZLY. hE JUST HAD IT BORED AND A NEW PISTON INSTALLED TO CORRECT PROBLEMS WITH SMOKING, DUE TO THE BAD RINGS,ETC. NOW IT BACK TOGETHER AND RUNS GREAT, AS FAR AS THE PREVIOUS PROBLEM, BUT NOW IT IS RUNNING HOT. IT HAS PLENTY OF FLUIDS, THE RADIATOR DOESN'T LEAK OR ANYTHING. IT DIDNOT RUN HOT BEFORE THE OVER-HAUL. ANY SUGGESTIONS?

 

Make sure that the thermostat was installed properly. There is a tab on the head and a small vent hole on the thermostat. They are suppose to line up with each other. Had similar issue with my 2000 Kodiak and that was the problem. It inhibits the water flow if they are not aligned properly.

 

also check and make sure you are not running too lean, since you reworked the engine it is drawing more air now. you might have to rejet the carb