So many people have great success putting the Nibbi PE30 on a ZS 250, and with larger pilot jets. Maybe a #30 will work.
The air screw is on the intake side, so opening it will lean it out (a true air screw). Based on others experiences with the carb, I would think that 2 turns out and setting the needle as low as it can go should be too lean even with a #32 pilot jet. It is really puzzling that you haven't been able to find good jetting conditions.
I will be watching this thread to see how your jetting changes go. The kit that I got also bottomed out at #32.
https://www.chinariders.net/showpost...3&postcount=25
Yes, it's a PE28, but I run a #42 and had to lift the needle (shimmed in my case) to enrich it a bit. If it was getting more air (PE30), I would probably need to increase the pilot jet size and/or close the air screw.