I purchased a 125cc chinese atv for my son for Christmas and already had cranking issues twice. The first time I replaced the battery, spark plug and cleaned the carb, and it started running again for about two weeks. Now it wont turn over it try's to start but drags and nothing happens. Also I noticed when I did get it to start that the headlight would dim when pressing the throttle to give it gas. The battery wont stay charged Im thinking just don't really know much about atv's. Can somebody please help?

 

Probably a bad regulator. Also can be a bad battery straight out of the box.Charge the battery up and load test it to see if it's ok. Check voltage at the battery while it's running. Should be at least 13+ volts on these to keep the battery charged.If it's showing battery voltage or less then regulators are the most common cause.

 

I tested the battery and it's showing good voltage. How can I test the regulator, and do you think I could have a bad stator because the lights won't turn on and the bike will not start now.

 

Voltage on a battery isn't always a good indicator as to its condition. Here's a good article on this and how to load test one.https://www.batterystuff.com/blog/ho...ry-is-bad.html Also on most machine you can pull the yellow wires from the stator leading to the regulator and check resistance between each one. Should have some resistance between each other and no yellow should short to ground.Once running and battery isn't charging,stator charge coil has been eliminated as the problem,then a faulty regulator is usually the cause.