air brush spitting paint

First thing I'd do is check the needle tip for damage/splitting under the highest magnification you have.

Also, this sounds pretty dumb but have you discharged your moisture trap? I had some spitting a year or so ago, and to my surprise and I still don't know why, my trap was full of water.

Just a couple ideas for you until the real airbrush experts chime in.

It sounds like the nozzle or needle tip is damaged.

It could be any number of things, but Airbrushes are nothing more than tiny paint spray guns. Same parts, same theory of operation. If a spray gun spits or sputters, one of the first things to check is that all the fittings are TIGHT, and that the air cap and fluid tip (on the end of the airbrush) are also tight. Anything loose breaks the vacuum pressure and causes inconsistent spraying.

I teach (real) Aircraft painting for a living.

Several possibilities, among them: Paint residue remaining in front end parts , split tip/nozzle, bent needle tip, rubber "O" ring damaged. Try a really thorough dis-assembly and cleaning, then a close visual inspection of the mentioned parts. I once experienced a very tiny split in the nozzle, required high magnification to find it. It was the Sotar from Badger, the airbrush was non operable with the split, replacement returned it to like new function.

Visit Don Wheelers airbrush website if you have not already, worlds of AB info to be had there, including the one you have. Good luck with the fix.

Patrick 

I own an Iwata Neo also and it just sprays beautifully. Have you properly stirred and thinned the paint? What psi are you using? Thick paint and low psi will cause this problem. Another issue may be bad paint. Have you tried others to see if there is any change?