I guess so cause it don’t wanna go in. I used my digital dial and check the new vs old and there was a very slight difference so slight that I didn’t think my cheap gage was being accurate ,it’s one form harbor freight
I also am using the 28mm pumpers. I used KY-5439N kits. I didnt need the needle jets as my original were good. I just measured the ones in the kit and the OD where the fit into the carb body is 5.21 mm
From the photos it appears that your carbs have fuel/air screws and don't have the pilot adjusters. They also have a pump on the bottom of #2 carb. I think you said your old needle jet was an O4? That would make the carbs either a '79 or '80 KZ1000 for the US market. (Canada was a bit different.) The needle used in '79 was a 5CN17 adjustable with 5 slots. In 1980 they used a 5CN29 needle with no adjusting slots. What needle is in your bike?
Edited to add that the '79 LTD used the same carbs but a larger needle jet....O6.
Edited again to add that sometimes the nets are a loose fit but sometimes they are like an interference fit. What I've done in the past for tight ones is to use a piece of wood dowel (and a small hammer) in the main jet tube to tap the needle jet into place.
I have a couple of Z1B's restored, an '80 KZ1000LTD restored, a 1981 KZ550 restored and a 2008 KLR 650 for off road fun. My wife has a 2019 Suzuki DR 650 for on and off road.