Possible vacuum leak, now with video

No, it makes sense but... if your number 3 carb's vacuum pull was way off you wouldn't be able to synch the others to it. On a different manufacturer's engine for instance, the number two carb's slide "closed" position is not adjustable. It is factory set. The vacuum pull you get on that carb is the baseline for the other carbs. If that vacuum pull is wrong, you have to fix that carb or cylinder or whatever you have to do to get the vacuum proper. This is not so on the Kaw as the number two carb could be way off just from the slide position.

When I mentioned your carb synch screw could be stripped I meant that maybe adjusting it isn't affecting the slide position on that carb. You think you are moving the slide up and down when you turn the screw and you are looking for the corresponding change on the gauge but you may not be moving the slide at all. Something to look at.
If you indeed have a leaky #3 cylinder then you wouldn't be able to get the proper vacuum to begin with. That's a game changer.

Thank you for all your help. Once I became privy to the fact that there is no baseline carb I set out to sync 2 to 3. Once I started syncing 2, 3 started to be effected and from there I was able to sync them all together and the bike runs very good. My next step is to adjust the valves, can anybody tell me what the gap is supposed to be? Is there a step by step on the forum somewhere?

Thanks again