Back-bubbling is when air travels backward through the paint cup, causing paint to bubble or gurgle rather than spray. It’s typically caused by a blocked or damaged nozzle that prevents paint from flowing forward, so pressurized air finds the path of least resistance — backward through the cup.
Common causes: Blocked nozzle (dried paint), bent needle tip, incorrectly seated nozzle, or crack in the nozzle.
Fix: Remove and inspect the nozzle. Soak in cleaning solution if clogged. Check the needle tip for bends. Ensure the nozzle is fully tightened (finger-tight plus a quarter turn with the nozzle wrench).
Related: Nozzle · Needle · Backflush Learn more: Airbrush Troubleshooting Guide