I think 350 is too much heat. Try using a heat gun for the initial paint application. Make sure you "fluff"the powder prior to dipping the hot metal. You want a thin dusting of powder. If it's too hot, the coating will boil, and leave air in the paint. I would try curing the coated heads at maybe 200-250'for a bit and see if that helps. Commercial dip pots have an air supply run through the powder to keep it from clumping and maintaining a thin coat. Good luck!