Seems like people have regular carb jetting problems as the most common problem with ATV's and motorcycles, I know I get a lot of questions directed my way about it. Below is a helpful video for those that want to diagnose the problem themselves.
First off I find most problems start with a less than clean fuel system. This is especially true with machines that have been sitting for 6 months or more. Also the smaller the carburetor the more sensitive it is to fine particles of dirt or debris from a fill up at the track or trail can affect the carburetor. This is one of the first things to be done before trying to diagnose any other fuel related problem.
Remember proper safety gear is always a must when using chemicals.