Sounds like it is missing. Pull the plugs and check them out. If one is black and the other is not, do a quick compression check. If both spark plugs look the same, do a tune up on it, including pulling the carb and cleaning it out. If the compression check shows low on one side, I'd be pulling the heads. It's a video and it is really hard to tell if it is distortion in the audio..... but I think I hear a leaking head gasket.
BTW: REALLY NICE 782!!