Hi, I have a Chinese brand ATV (Coolster). It's only a couple years old and barely used. It was running well but then just could not get started one day. I have replaced the carburetor with a new one. It does have spark at the plug, it is getting fuel to the carb, oil is fine, and it does turn over just fine. I just can't get it to fire up and don't know why. Any advice on what to try?