Moisture traps and moisture in the airbrush line

Nope, it's "Something Else".  You are experiencing "Tip Dry" which is common when using acrylics.  I also suspect that the reason it is drying so badly and the reason that you are seeing some come out thinner is for the same reason:  It isn't getting fully blended.

Use acrylic retarder or a different thinner to help with the "Tip Dry".  Mix your paint and reducer in a bottle or smooth cup and then pour it into the paint cup.  It is difficult to get thorough blending when you try and mix the paint and reducer in the paint cup on the airbrush.

I don't know anything about the Iwata line of airbrushes but yours may have to fine a nozzle.  The pigments in modeling paint are frequently quite large and won't flow well through very fine nozzles, especially when the needle is barely pulled back.  Might not be an issue, I'm just not familiar with that airbrush since all of mine are Badgers.

Thanks. I didn't know what the heck was going on. I've been airbrushing for a couple of years now I guess and I've never had that happen before. I've had to swab the needle with a Q-tip, but never fought it like I had to that time.

What advice for preventing this, on top of mixing outside the brush?

What advice for preventing this, on top of mixing outside the brush?

As I mentioned:

Use acrylic retarder or a different thinner to help with the "Tip Dry".

I have NEVER had success with MM Acryl Dark Green!

Ever!

I switch to Enamel for my dark green if I am using Acryl. But nine times out of ten I get fed up messign with the Acryl and grab my Tamiya.

David

Before the demise of my 335 I was going to use Vallejo Game Color Cayman Green to go over the screwed up dark green, since I've never had trouble with Vallejos.

I really like a lot of Tamiya's colors and they work with the airbrush really well, but I just can't seem to get a decent gloss coat to go over them, which is why I've been experimenting with some other paints like Acryl. Maybe I'll ask a question about that.

I'm gonna play with some Vallejos and see how they turn out over a primer. I've used them plenty on minis, but models have too much area that gets handled and they have a lot of rub off from the little bit I've used them on any models.