Bike chain?

My 2004 Yamoto 150cc bike chain keep falling off whenever I floor it on first gear. But once I get it started, it stays on. I tried tightening it bit it kept falling off. Maybe I was tightening it wrong? It would get tighter and be better but then after a while it'd fall off again. Help?
 
you need to remember to check your wheel bearings and the bearings and or bushings in the swingarm as well. they can be moving while you are in motion, throwing out the alignment etc. sometimes the rear sprocket is mounted into a drive unit that has a bearing or bushing too, along with some rubber dampers. good time to check all of that.
 
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