Agreed.
It looked like spray out of the main to me at first while watching, but it can't pressurize the bowl to make that happen because of the vent. And no way enough accelerator pump fuel got in there to make that amount of spray for several strokes. So, my guess is it's sucking (some) fuel thru the low circuit and blowing back out just as fast.

Without some history of the engine, best we can do is offer possibilities but it's obviously been apart to some degree evidenced by the aftermarket tappet guide covers. Could be simple as an improperly adjusted push rod (if it has adjustables), or a bad lifter, stuck at the top from sitting so long, holding a valve slightly open. Those would be the easiest to correct. Otherwise, the cam out of time or bad valve/seat/guide would have to be the issue.

I would do a simple compression test in hopes of finding a culprit cylinder and go from there...

 

After looking at the video on a big screen I can see more clearly that you do have a compression issue as I stated back in post 22. you definitely need to do a compression test... You can see where one cylinder is good because the diaphragm is lifting the needle, but one intake is definitely not closing 100%. As asked by others, what pushrods are in the bike? time to open it up. Could even be a lifter that won't bleed down...