[Ashlandchris]

I also think the pressure was a bit low, but my cheap compressor can't be turned up (see image below)

So I have bought a slightly beefier compressor and that seems to have made a big difference.
I also found that my bd181 brush seemed to "spit" and it seems related to paint building up in the nozzle discharge area. I notice that the bd181 has little "v" notches cut into the nozzle, while my new iwata doesn't so I have taken the screw off nozzle bit from the "free airbrush" that came with the cheap compressor and swapped it for the v-notched one. The spitting issue seems to have gone away now and I have 2 good working airbrushes now.

Time to get painting