What was the temperature and the ambient humidity? That is important. But more important is a good primer base. Usually a thin first coat of etch, then a thin hi-bild primer coat lightly sand, a second thin coat .. lightly sand then the top coats. As Clark said, a number of thin coats are better than a thick coat. It appears that 2 things are happening here. No etching primer and too much primer coming out of the gun. Turn down the proper adjustment screw on the gun that controls the product feed rate. Also, make sure that your air pattern is correct.
Temp 77 F Humidity 52% used acrylic lacquer primer thinned with lacquer thinner. These parts have been sitting around for 3+ years with a phosphoric acid type coating for rust inhibition. (which is supposed to provide proper etching)
They were rinsed and dried before painting. During painting, noticed the flaking, so wiped the piece down with thinner and started over--same results. Parts shown above are forged steel pieces of Univ. Mounting frame, did notice the cast pieces of the frames also wanted to flake. Have since used liquid soap and water with SS scrubber to remove all remaining paint and hopefully rough up the metal a bit.
Don't know if that was the problem, or as you said, too much paint, wrong thinner, not enough flash between coats........and so on--So many variables
Will stay with it and see if I can figure out the problem. Further suggestions solicited
Got 4+ inches rain yesterday, so painting will be on hold till humidity drops--current 70-90%