praire 200 automatic.

I bought this quad for my little brother and when driving its kinda bucking. Like Rev - Dead-rev -dead -rev-dead. Just like when you go in reverse it kinda gives out like no spark so you cant go fast.
Well its happening while going foward now and im not sure how to fix this.
and its cutting out consistently so i doubt its a carb thing. If i hold the gas down while its doing this it will back fire and stuff. At the same time it cuts out the lights dim. The electric start wont work, i think the battery is dead.
I would imagine it is an eletrical problem. Please help my bro is out here untill tommorow and wants to get some riding in.

Any input greatly appreciated.

 

thats a 300 automatic, sorry