Sounds like the paint is still to thick. Thin more. That brush uses a .3mm nozzle, very fine. Most of the more popular brushes used for modeling type media use a .5mm nozzle. Your brush is made for very, very fine work and that requires very thin paint. What is your ratio of paint and thinner? How much air pressure are you using? My Iwata Cr has a.5mm nozzle and I typically thin about 1 to 1 depending on the paint. Or half thinner and half paint. I use around 12 to 20 psi depending, again, on a few factors.
Give more thinner a try. And remember, you have a very advanced brush for a beginner. Those tiny nozzles can try the patience sometimes, even for those with more experiance. Your learning curve with that brush is liable to be very steep.
Something to take note of: The thicker the paint, the higher the pressure. And vice versa.