New Member. Second Bike, First KZ!

Hello All! New Member, Just Purchased this 1981 KZ440B(2?) for $400!! Couldn't pass up that deal. Super Excited to have a second bike to keep stock! First bike is a 1975 CB360T that I fully tore down and customized brat(ish) style. I'll post pics of that too if ya want.
So the KZ starts up and runs, but it backfires out the intake quite a bit. I checked the carbs for air leaks (they are good), checked the float lvl (good), inside of carbs are clean, valve clearance is within spec, spark plugs gaps are good. Checked the points and found out this model has electronic ignition, so not sure how to check if that is good. On the list I still plan to rebuild the petcock once the kit comes in, for now I just keep it on Prime just in case and it is flowing. And I'm going to fidget with the Primary Pilot screws. I'll try to upload or link a video of it running soon.
Any other suggestions are appreciated as I'm only familiar with my CB360.
Thanks in advance ya'll!

Here is a video showing the backfiring. After some research into the backfiring/slow rev resxponse, it sounds like it is running very lean? My main question is where do i even start fixing that, the main pilot fuel jet? Being self taught in all this is very frustrating, as soon as i feel like i know a lot about these bikes, something else happens and i have no idea what i'm doing... then again i keep coming back so, maybe i'm a sadist?

imgur.com/IiBULln

Have you checked the diaphragms in the carbs? They are under the big covers at the very top of the carbs. If they are original, chances are they have hidden pinholes which affect the slide lift when accelerating.

Also, check the intake rubbers (carb to engine) for cracks.

Is that vice grips in the video holding a vacuum line closed on carb #2? Cant see if there is an open vacuum nipple on #1. If so should have a rubber cap.

Checked the diaphrams today, they look in good shape, The previous owner did say rebuilding the carbs was the last thing they did to the bike.

Also, the intake rubbers look new as well, sprayed them a few times with starter fluid to check for air leaks and they are good. I will be going through the carbs completely in the next week or so because i'm convinced it is something with the mix. I will update when that is complete.