Oh, my God! I can't believe that no one has figured out the real problem - IT'S YOUR COMPRESSOR!! NOT THE AIRBRUSH!! NEWBIES!!  :  When you get sputtering - that's WATER in the line getting into your paint. This is because you don't have an inline filter/water evaporator attached to your tank/compressor. If you're using compressed air it'll still do the same thing. Cold air coming into contact with warm air in the line condeses, and becomes WATER. This makes any airbrush spatter like this. I learned this with my Paasche earlier this year when it did the same thing. It's because warm air is going into the cold tank, and causing condensation in the air. This becomes even worse as the tank becomes more dry (less air), and picks up water droplets, and puts them into the airhose. I've had this same problem before, but I never really thought of it until I got a new compressor with a reserve tank. The old one ran all the time, so it wouldn't store cold air - instead you got water droplets after it sat a while. Once warm it sprayed as usual. But when cold - it did the same thing that you described here. I hope this helps someone from making a costly shipping mistake!