Not sure what a 'packing nut' is, I have Iwata's with that large self centering nozzle. I do have started to clean the nozzle opening, in addition to the nozzle, which I like to think helped a little. But the biggest gain was probably proper thinning of paint AND equally important, sifting my paint/primer to avoid clogging.
I noticed some time ago, that when I sprayed water, when pushing out only air, tiny droplets of water came out which is not good. Unsure why that happened. If, unclean parts, or badly manufactured parts, or.. maybe I should have given the needle a slight tap with my finger after inserting it into the airbrush (an advice I saw on youtube which I now follow).
Hm, packing nut. I wonder if that could be the tiny screw inside the airbrush (when removing the rear part) that I think tightens the tiny o-ring behind the paint cup where the needles is pulled back into. I haven't been able to adjust that screw to my satisfaction, so I have just left it as is. Ah, it makes sense I guess that this screw isn't too tight, but I don't have any personal experience with such an issue I will admit.
10. June, 15:41