Good evening all!
Just wanted to share my experience recently with a problem I had with one of my airbrushes (I have a "thing" for airbrushes - I buy airbrushes like my wife buy shoes. Just can't walk past the airbrush counter at the hobby store).
I bought an Iwata Neo CN when it was just released here in Canada - about 2 years ago or so (cheap, too good a deal to pass by). Notwithstanding all the horror stories one hear about the Neo series, mine worked fantastically well - so much so that my other Iwatas were used less and less. Until a couple of weeks ago....
I was working on laying down the camo pattern on a PCM Hawker Tempest, airbrush working perfectly all afternoon, as always. Next day I want to continue, and for the first time I was having issues - spitting, paint starts then stops, bubbles forming in the cup.... Take airbrush apart, and clean it (again) - still problems. I Googled around and from Don's Airbrush Tips a suggestion was that the tip ("nozzle" as Iwata calls it) may be cracked. So I examine the tip, see nothing wrong, take out a magnifying glass, still don't see anything wrong...
Eventually remember that I have access to a microscope (optical) and decided to try that. Lo and behold, under 200X magnification there is a crack visible in the tip, so big that it looks like part of the grand canyon. I was pretty baffled that I could not see a crack that size with at least a magnifying glass, try again using the naked eye & magnifying glass - the tip/nozzle looks perfectly fine. Put it back under the microscope - Yup, the crack is STILL there!
I ordered a new tip from Coast Airbrush and they delivered it three days later, I installed it and the airbrush is back to normal again. I have no idea how the nozzle cracked, suffice to say that I will be SUPER careful in future - no bumps etc if I can help it....
So if you are having inexplicable issues with your airbrush - and especially if you notice bubbles forming in the cup - it may be time for a new tip (or "nozzle" if you like).