it looks like we have the same carbs and jet sizes and I have a cb750. Anyways when I was rebuilding my bike I had the same issues. After gapping my valves, adjusting my chain, bench sync carbs, gapping points and timing the f mark. I was getting the same popping and stumbling, bike was running lean.
A few things That I had to go through was that my exhaust headers weren't sealed right, exhaust fumes were coming out after it would warm up, had to retorque. A couple of rubber boots had a hairline crack, bought new boots. Carb bench sync were wrong and had to redo and lower the slides to the point of almost closed. I had diachii points, needed to get Tec points and new condensers. I also checked my spark plug caps and wires and trimmed the ends to make sure my plug cap had fresh copper/contact and that caps weren't cracked because those thing get really hot and I heard they can cause funky issues. I feel like I'm missing one more step but can't remember.
I read ur thread and the only thing that stuck out was that you never mention if you gapped ur valves and in ur picture the carbs slide seemed a little higher than what I got but I can't really tell, for all I know they could b all the way down. One thing I do know u r running lean. My plugs are light chocolate brown, the colors change during spring and fall, I think they change the recipe in the gas up here when winter moves in..
Good luck
