I built a T-Burner for my first forge I built. The first night I had a rough forge made and the burner built I put them together and ran it for like 10 minutes no problem. It still runs great with a reducer outside of the forge but once I put the coupler on, or the reducer for that matter, and put it in the forge it sputters.
The coupler and reducer are flame holders and I don't see it being a fuel delivery issue since outside of the forge it has no issues whatsoever. The regulator I have is 30 PSI adjustable and I was testing from 5-15 PSI with no luck at any area, also it worked perfect