Difficulty airbrushing fine lines with metalizer paints.

I've been having this problem for the last year or so but have never really found the answer yet.

Everytime I try to spray a fine line with metalizer paints (either Testors or Alclad II)
I get skipping and spidery splotches.

I have 3 airbrushes and they all behave the same way. I have an Iwata Eclipse BCS, HP-C and a Highline -BH (picked it up yesterday on sale). It can't be a question of a damaged airbrush as all 3 of them were brand new and behaved this way right out of the box.

I have tried different air pressures (5 to 45psi) with no success. What basically happens is that when I hold the brush very close to the surface and ease the trigger back nothing comes out. I keep easing it back a little more and then all of a sudden 'bam!' I get a nice splotch. Sometimes I do get a fine line but then it stops after an inch and then starts again, and then splotches, etc.

I don't have this problem with my Tamiya acrylics or Testors enamels (I thin them properly) - just the metalizer paints. I tried Alcad II for the first time this week in hopes that it was just the Testors that was causing the problem but it's the same bloody thing.

Am I missing something here? Usually a problem like this is caused by improperly thinned paint but the Alclad paints specifically state not to thin them.

I really need to resolve this issue as I'm currently working on the Tamiya F16CJ and want to do some fine metallic shading of the engine but I dont want to ruin the paint job with splotches & erratic lines.

It's almost like there's surface tension in the paint cup and needs a larger needle opening to flow.

Any suggestions are appreciated.