MM spray problem

I would suspect that you need additional thinning, in spite of what is written on your paint bottles.  I've heard that MM Acryls are "supposedly" airbrush ready from the bottle, but none of the MM Acryls that I have indicate that they are airbrush ready and they all definitely need normal thinning prior to use.  Additionally, I have seen enough batch to to batch variation where some bottles of paint need little or no thinning, and other need a lot of thinner added.

So disregard the "airbrush ready" and add as much thinner as needed.

Use a retarde for the acrylic, water is by far the cheapest way.  What is happening is that the paint is drying in the brush before it gets out of the brush.

Are you using the correct thinner?  Make sure you're using Model Master Acryl Thinner.

Jesse