I thought that the FA (fuel/air) pickup tube from an old Coleman suitcase stove of mine might be malfunctioning. (A 425C two-burner, perhaps? I don't know. I now have only the tank.) So I searched for information on exactly how these tubes work, and found what I wanted on the Coleman Collectors Forum website. Below we see a page of text and a diagram from what appears to be a piece of Coleman literature from about 1960. https://drive.google.com/file/d/0B4_5mgrc2IliZTNOc3BORWRPVzQ/view Fascinating! I had always thought that in "instant-light" mode, with the central rod down and blocking the orifice at the bottom, only fuel vapor from the fount went up and out the "generator". Instead, atomized droplets of fuel, plus air and vapor, go up and out. Apparently, the small amount of liquid fuel initially present in the pickup tube goes up the inner tube and is not replenished, except, maybe, by a tiny amount that sneaks through the orifice alongside the rod; any that does sneak by gets atomized by the air/vapor rushing up through the inner tube. Also, I had always wondered how the air/vapor flow gets blocked in liquid "run" mode so that only liquid fuel then goes up the tube. Well, when the central rod lifts and opens the orifice at the bottom, fuel rises up into the pickup tube to match the level of fuel in the fount outside the pickup tube. Equilibrations of pressure keep the level at that height. No additional air/vapor then can pass into the air inlet hole at the top of the outer tube. Magic. The three time-sequence diagrams below show these stages clearly (Coleman Fuel Valve Operation Diagram - The Coleman Collectors Forum). Ignore, in the diagrams, the spring and the way in which the valve stem controls the up-down movement of the rod (and ignore the parts laid out in the lower right). This graphic shows the FA tube in a Coleman lantern. In a typical old Coleman stove, one moves the rod up or down with a lever. In all other respects, the FA tube in a stove is essentially identical. Note how, in the middle diagram, in "instant-light" mode, with the rod down and blocking, mainly air/vapor passes down between the outer and inner tubes and then up the inner tube. Then in "run" (liquid) mode (third diagram), the fuel levels in the fount and between the tubes are equalized, thereby blocking the passage of air. So, what did this knowledge tell me about my perceived "problem" with my FA tube? I was concerned that the outer tube was "loose": it was able to twirl around within its crimped connection at the top. This crimped connection is shown about 1/3 of the way down in the second image I posted. I believe now that this "looseness" doesn't matter. No fettling required.