You might just have some trash or water in the fuel. Drain the float bowl on the carb and see if the fuel is good and clean. It might be best if you remove the carb and clean it. The pilot jet might be stopped up. Make sure air filter is clean and airbox is fully assembled. Change spark plug. Is the camshaft good. Really need more information exactly what type of problem you have. Have you owned this atv for a while or just buy it?