Im havin trouble with my 250 atv, i get it started but it has a high and violently loud idle. Ive messed wit the idle screw but nothins happenin. Any ideas what it is and what i can do?

 

Sounds like it's sucking air from somewhere, maybe the intake boot try spraying carb. cleaner or starting fluid between the carb. and cylinder on the intake boot if it revs up then there's your problem. I am not too keen on the chinese engines but they all work basically the same. also try spraying the top where the throttle cable goes in it may be loose up there.