Ok so I have a 125cc atv, thought it was a peace? I cant find it any where! Plastics were eagle, but no luck finding it! Anyway I have rebuilt it an have rode it, good times. Every time it does good for a minute then throws the chain. I have adjusted it, an new chain! Still happened. when I first put the new chain on, left it tight as I know it would stretch! An wow did it, but never popped off or had any problems for hours! Tightened it, rode a little, an chain popped, then it broke. At this point I'm going for new an new better chain! Any advice?

 

Make sure the rear axel is horizontal with the front wheels, if you want to be really pedantic measure the distance between front left wheel and rear right wheel, and make sure both sides is the same, an axle off centre can cause chain to throw, if that's is all okay, check that the rear axle sprocket isn't bent,warped or twisted in any part. If that's all good check front sprocket.

Is the chain coming off at rear or front, I mean once it throws does it stay on front sprocket so u can slip it partial on the back one and roll it backwards to get it back on ??