so i just picked up this little atv and it starts ok revs and drived good, plenty of go to it, no cutting out but it does have an idle issue, it wasnt idling so i pulled the carb(25mm mikuni) took it apart and cleaned all the sand out of it, well i got it to idle, but its very rapid, it idles high then low and dies, restarts just fine, randomly it will idle ok then idle high then low again. the carb is a little beat up so im thinking of just replacing it, but i could use some idea's on whats going on?

 

Sounds like it could be:
A seal leaking/ still something in the carb/ something wrong in the carb slide allowing the needle to float.