On venturi burners ( atmospheric) there are several things that cause problems that are sometimes hard to figure out.
One is too low pressure, another is too high pressure. Too low and the flame wants to climb back in the burner tube, causing sputtering and squealing.
Too high and it blows out, then reignites, causing sputtering and popping.
Also, if the burner tube ,or the flare, sticks out in the chamber, it heats up. Once it gets hot enough, the flame wants to ignite too soon, and tries to burn back in the tube, where the heat ignites it.
Placement of the jet tube is critical, and must be set at the forge site. Even if it was set at the factory, differences in equipment,altitude, and other things can change how the venturi draws air.
Some solutions to all these are:
1)Make sure the orifice is clear and the proper size. It should be pointing straight down the center of the burner.
2)Make sure the jet tube (with the orifice on the end) is placed in the exact spot to create the venturi.
3)Make sure the forge has enough exhaust porting to allow the chamber pressure to stay low enough to prevent back pressure in the burner tube.Too high a chamber pressure will cause collapse of the venturi, causing sputtering or flame-out. With the forge running at full blast, and up to high heat, there is a lot of hot expanded gas trying to get out the ports. Most forges are designed to have big enough openings. Block one up and you cut the exhaust porting in half. (Try putting a 1" tail pipe on your V-8 and see how it runs.)
4)Make sure the burner flare or burner tube is not projecting into the chamber. The flare should be about 1/2 to 3/4" back, smoothly bedded in a cone of refractory. The burner tube should be placed so it is just at the start of the flare, or slightly back from that point.
5)Raise or lower the pressure and observe the changes.
6) As pointed out, adding a damper plate to the air port can make fine tuning easier.
7) Change to a blown burner and eliminate most of these problems.
Stacy