Can paint be thickened??

mmmh, dificult question. I believe that art stores sell thick acrilic media. this is a thick gel/cream like substance that gives your paint mode "body" cq thickens it. I don't know if it compatibel with the paint you're using. And I also don't kmow if you can airbrush it. But this is the only product I can think of that could help you.

I think you'd be better off putting down a light colored primer coat then just airbrushing several thin coats of the yellow. I might take a while, but you'll get coverage after a bit, and it should end up looking good. Use a light gray or white primer underneath the yellow.

The easiest (maybe not the fastest) would be to leave the cap off and stir it every few hours. Letting the carrier evaporate will thicken paint.

Model Master Acryl is meant to be airbrushed straight from the bottle, and yellows and whites in general also are difficult to get good coverage with.

Maddafinga's suggestion to use a light primer and several coats is a good one, and I would add that you may want to increase the distance between your airbrush and model. This will allow the paint to dry a bit mid-air (but you don't want it so dry you get a grainy texture).

Thanks for the suggestions. I probably will go with the primer and then try the yellow again.