BTW, Your chain is loose. Way loose. omg loose. I even noticed in your video that some of the links are binding.
If your chain has a riveted link, then adjust it while the bike is on the side stand. If not see above post. I adjust mine to where the chain almost touches the swing arm when you press the bottom run up to the swingarm, midway 'tween the front and rear sprockets.
However I would lay money that you have the original chain, as most chains last 20K and I bet that the previous owner said, "WTF, I'm selling her after all so why dump 200 bucks on her". Ride the motorsickle like an old lady and the chain kit last closer to ... 27K! Notice I wrote 'kit' (two sprockets and a chain.)
