So I should thank you all for asking lots of questions, as I realized I am doing some things wrong. First was the mention of a plinth block under the crucible and I see that MIFCO sells them and there wasn't one with this used furnace. I see there is a bunch of slag in the bottom of the furnace that I should remove and the firebrick in the exhaust port needs to have the mortar repaired. I can see that a plinth block under the crucible will bring it up almost into the lid. So it may heat better and keep furnace gases out of the metal. This furnace has a double cover and the ID of the hole in the main lid is 7". So it will be much easier to charge the furnace with the crucible raised. I reshaped my grab & pour tongs a bit with a grinder and now it is easy to use in the furnace. I did as asked and took a bunch of pictures. In the process I also discovered the furnace has a stop where you push the burner into. I had it too far out. I found the manual for the furnace at MIFCOs web site and it has lots of useful information. They also sell repair and relining kits. I attached two pages from the manual that are quite important to understanding the burner. In the photos I took you can see that the pipe in the side of the furnace jacket is a 2-3/8" OD and the burner pipe is 1-1/2" Sch 40 pipe. There is a bulged area, apparently made from 2" Sch 40 pipe with the ends rolled in to fit against the 1-1/2" pipe on the furnace end and reduced to a 1" pipe on the blower end. That bulged area is really important for a natural gas fired furnace as you can see from the drawing! It is a venturi that accelerates the combustion air and creates a Vacuum in that chamber to actually suck the gas in. Natural gas is supplied at really low pressures so the blower could very well blow out the flame by cutting off the gas flow. So this venturi keeps the gas flowing. I also attached the BOM so you can see what parts were used. I think a big part of the cost of this furnace was in the controls. There is an electric gas valve, motor starter for the blower, a pressure switch for the air and a UV sensor and fire eye controller. This came out of a school and was used indoors so safety was very important.