It's a "jet" burner which is really just a generic term for a wide open mix pipe. Any burner design requires that the injection of the fuel is able to pull in air that it will mix with prior to being ignited. This one seems to shoot the fuel past an adjustable opening, it mixes with the air in the large tube and then burns on the way out. I've also seen a similar design that has a small circular plate of metal mounted about an inch above the opening so as to diffuse the flame into a circle instead of a point.
Mine is similar to the one in caver95's post, but I am using a orifice out of a natural gas burner from a furnace that is on the end of a 1/8"X4" nipple that I can adjust up or down in the burner tube. I have not calculated the btu output yet, but It does sound like a jet engine when I run it full open. The bottom T fitting is 1-1/2 and the burner tube is a 1"X12" pipe nipple with the threads cut off the top. Here is a link to a drawing of one that is similar.http://www.abana.org/ronreil/Sidearm.jpg
What is the ultimate effect of moving the orifice further up into the mixing chamber? Do you get a different kind of burn or is it something that needs to be adjusted in concert with the air intake?