I have a 97 KingQuad that starts great, idles great but will not rev up. I drained gas and put in new, changes spark plug and sprayed a little carb cleaner in and still the same. May be running rich because the spark plug was black and sooty. I'm real handy with farm equipment but not so familiar with these small engines. Any ideas what to check next.

 

Yea sounds like its running rich, had the same problem on my Honda 300fourtrax, if you can take the carb off and clean it real good and put a smaller size main jet in it, you probably wont have to worry about the pilot jet, and some times if you dont keep that air filter clean they will rich in a heartbeat, this may help you some