This is usually caused by improper triggering technique. To do a line , push down for air, start moving in your desired direction, then pull back for paint, at the end while moving slowly move the trigger forward to stop paint flow, then let off the air. This should give you nice lines with a bit of practice. A lot of things in the beginning are pace and technique. Training your brain and hands to do everything in the correct order.
if this doesnt solve your issue. Break down your airbrush and clean and inspect the nozzle. May be some old gunk stuck in the nozzle not allowing the needle to fully seat. Be gentle with the nozzle they can crack and give you all kinda if headaches.
Hi Tcalvin, I'd say you need to make sure you are still moving your airbrush as you push the trigger forward to stop the paint. You don't need to lift your finger to turn the air off after each line. Keep the air on, start moving, then pull back for paint, push forward to stop paint while still moving and leave the air on, go down to the next line and repeat.
I believe that as you are slowly closing off the paint flow you get a bit increased pressure from the nozzle it can push a small blob out so I try never to push the needle fully forward to seat it but just enough to stop paint flow. I have noticed that pushing the needle to seat on the nozzle that blob that the needle pushes out hits the paper as one big blop.
You may need to adjust the speed you are moving at the very end of the stroke as well.
A split nozzle will give similar effects so you may want to check that.