Trouble Spraying High Build Primer

I talked to Barry and he said temp shouldn't be an issue. What is common is the plug at the top of the gun doesn't allow enough air in. He suggested opening it up with a 1/8th drill bit. He also said because it started spraying nice towards the end of the cup, the air tip was probably clogged and it got blown out.

He suggested a little reducer shot through it before respraying as that will melt any residual.