Are you using a .35mm tip with the Iwata? I've found that for general airbrushing the .5 tip is better...either that or thin the 1200 more if it isn't spraying smoothly. Thinning it to the consistency of skim milk using a .5 tip on my HP-CS is what works for me. I think you'd really have to thin it down even more for it to spray smoothly using a .35 tip.