No idea from watching / listening to the video.....have heard a lot, lot worse than that though in real life, ie, not on a video. What makes you think it's primary chain? Cleaning carbs and fitting new kits does not aid in anyway the the actual critical functioning or set up of the carbs. That's done by syncing them all and fine adjustments of air / mixture ratios.
Edit...it could just be a clutch basket rattle, which is very common on these bikes.