Using HP-C (with adjustable handle) I am finding when using poly scale acrylic paint that I will spray for about 10 seconds then the paint builds up on the needle. Should build up be that fast? What can be the cause

have you thinned it enough/ or to far away from the kit paint may be drying too quick on leaving the A/b causing the build up

It may not be thinned enough

It probably needs thinning. Also, I like to use a tooth brush moistened with brush cleaner to scrub the front of the nozzle every now and then as I am working. It helps cut down on the build-up

I think I should have been more specific: Is it normal for the paint to build up so quickly (15 or less seconds?). i realize that it will build up but that quick?

All acrylic paints suffer from this effect. You need to keep the pressure low and the paint heavily thinned to avoid it. The advice about cleaning the needle with thinners is the best solution in the short term. I probably do this up to 100 times in a long spraying session of 30 minutes or more.

Poly scale paints are notorious for doing this...

I use an Iwata HP-B and have the same problem. They sort of coagulate and spatter like crazy in no time at all. I tried thinning them with everything from Isopropyl alcohol, distilled water, windex, windshield washer fluid.... you name it. Still clogged up...

I just don't spray them anymore.... I even added dishwashing soap (a couple of drops) to the mix to try and reduce the surface tension.... didn't clog as fast...but still clogged up.

Sorry i don't have better news... If you get yours to work out... lemme know! I am curious as well.

Later-
Jeff