Ink climbing up the needle bar...

[Panos tattoo]

sometimes it does happen either because the needle is too close to the tube or something blocks ink from the tip.petroleum jel,tiny piece of paper, tissue,or even small hair that blogged in tip ,allow the needle to move as if nothing is wrong but dont leave ink to flow in the front narrow part of the tip causing it to stock in the chamber and eventually ride up the tube.this happens after some time of working.if it starts as soon as you start to work its probably because the machine works very fast or in case of coils ,too much spring tension.this makes the needle travel so "violently" that creates a sucking effect which makes ink travel up the tube(try to imagine the move when you draw liquid with an injection.) .its easier to happen with large group needles.

[Mozzer337]

Try a bigger tube. One size up from your needle grouping. I always had ink flow problems, never really went up the tube, but because I have a lot of needle hang, I never got the required ink flow to the skin. Going up a size fixed it.