I am having difficulty with spraying polyspray.

I am using a HVLP gun provided by a person who used to do auto body work. Spray temperature varies from 72F to 82F. This morning was 72F and I chilled the polyspray prior to use. Diluting 4:1 per the spec. I get "chaff" when I spray - bits of coagulated paint randomly distrusted (not all the time). The bits are about 1/32 inch and some as long as 1/4". I am careful to put the spray on wet.
I had no difficulty with the polybrush. The gun appears to be clean. when I spray a test pattern, it seems ok. I am running about 20 psi in operation.


Any advice would be helpful.
Thanks
tom