Rick, you are correct. The Svea 123 has a self-cleaning jet; at least the later versions do. If you turn the valve counter-clockwise more than about one turn, a needle comes up and pushes dirt out of the jet. In doing so, it will shut off the flow of fuel.

Your Svea 123 has the self-cleaning jet if the valve stem body slopes down about 10 degrees from the burner riser. If the valve stem is at a right angle to the riser, then you have the older version that is not self cleaning. The older version comes with a tool, a small piece of fine piano wire mounted on a handle, for cleaning the jet. I have been firmly told that the older version works better and is more reliable. I have not found that to be the case.