Appears to have one cylinder not hitting with the same amount of punch as the others.
The idle mixture screw over #1 and #3 will be a balancing act at best with the PCV hooked like it is. Make #1 hit strong and #3 will be rich. Make #3 hit strong and #1 will be lean.
Look back at one of the old videos with the 870 carburetor. The engine ran a little smoother.
https://www.youtube.com/watch?v=LeOqYtY0Dng
Clay