For the bubbles in your cup:
Paint to thick and clogging your tip - reduce paint.
Paint has too much reducer and creating tip dry - add more paint.
Crud in the nozzle tip. Remove nozzle (after emptying the paint) and give a good deep clean. A long bristle hairy brush is really good at getting into the nozzle.
A split or flared nozzle. Replace nozzle
An air leak from the air cap. Use beeswax (chapstick will suffice) use a cocktail stick and put a little on the threads - too much can clog your air channels. This usually fixes 80% of leaks. try it and see if it makes a difference.
*** remember that all threads on an airbrush only need to be finger tight, you don’t need a spammer/wrench to tighten them as much as possible- you will cause damage to delicate threads guaranteed ***