Need some Assistance and idea's on a problem
 

I have a 2003 eton yukon cxl 150, my parents bought it for my younger brother, it ran fine up until about 3 years ago, it was rebuilt bottom up, now to the problem that I'm experiencing is the bike will start and idle, when you give it throttle it shuts off, if you put it in reverse it will idle and run fine, if you put it in forward it jumps at first and like stutters about until it gets up in speed then runs fine. I can't be sure if it has something to do with the neutral safety switch or the cdi unit but any other ideas or help with getting it running properly again would be nice. I know theyre not the best atv's out there but it's what i have and would like to get it running for my brother