I built this forge about 3 months ago. I am having a problem with the flame "snuffing out" when the chamber gets hot. The forge is built out of a 12" pipe, lined with kao wool, and three fire bricks internally, one on the bottom, and one on each side. It runs good for about 10 to 15 minutes, but as soon as it gets a little hot, the flame snuffs out, and restarts itself from the heat in the chamber. The hotter it gets the worse the problem gets. I notice the internal burner is glowing red hot when the problem starts to happen. The internal burner is about 5" from the bottom fire brick. The burner is a 1-1/4" tee reduced to 1", and is inserted into a stationary 1-1/4" pipe that goes about 3" into the chamber. But like I said it burns great until it gets hot. Any help to this newbie is appreciated. Thanks