TORS.........nuff said..
haha, but really, unplug the little black box under the gas tank, to the left of the coil. then, you can get it to idle. now, for the chain jumping. grab the rear grab bar and shove it side-side. you should be able to see the swingarm move with slack in the pivot bearings. next, grab the sprocket and see how much play is on the splines. they will wear out enough for it to skip across the splines under load, and you will end up having to replace the hub and likely axle. if you don't find alot of play, then, ratchet strap the swing arm to the frame by hooking to the upper carrier bolt tube and suck it untill the sprockets and pivot bolt line up strait, and tighten up the slack in the chain, and try it out. i'm assuming you already inspected the sprockets. if you run out of adjustment, and have stock sprockets/swinger, then it's time for a new chain.