First time this has happened, one of my airbrushes (top feed gravity) won't spray, in the cup the paint bubbles and shoots out of the cup, just spent 2 hours taking it apart and cleaning every part, still does it, any ideas?

Did you clean nice the hole on the cup cover?

The only time I ever get blowback in the cup is when there is indeed a clog. If you've scrubbed it thoroughly and you're sure there's no paint in there then check the little rubber o-ring inside. Some models have them others may not. I use Iwata HPC and HPB. On occasion the o-rings were wrenched in there too tight. You'll know if that may be part of the problem because it will be tough to feed the needle through.(Or they could be worn down and need replacing) If that doesn't do it then what I often do is mix 50 /50 hot water and rubbing alcohol and let the airbrush soak (dismantled) in the solution for a few minutes then scrub it again. If its acrylic paint you've got in there the alcohol will help dissolve it and scrubbing it out may be a bit easier. It may just be a trial and error thing for you. But I'm willing to bet there's something stuck in there somewhere.