Hi all, glad to have all the different perspectives added to mine. In watching them run, I note they all sweat moisture immediately, and postulate since the basic exhaust of an alcohol burner is water vapor and carbon dioxide, the moisture immediately mixes with any oil residue making a sticky emulsion. When I spin my cold engine over, it spins freely, but four or five cycles of burner input has it sticking, and I can stick a cotton swab in the port and pull out yellow emulsion. When I wash it out with WD, I immediately get high speed, the feeling of the solvent burning in addition to the alcohol, adding to the expansion during the valve open, and it generally gets hot enough no water condenses on either the valve or the head and cylinder, leaving just the oil residue. I've seen the additional valve in some, and have seen a ball sitting by its weight to allow the cooled air to exhaust without going through the port, so I may try this with the next one I'm in the middle of, as there is definitely a volume of air left in the cylinder when it has cooled, causing the pop and blowing out flame. The alcohol and the butane are the fuels of choice because they leave so little partially burned hydrocarbons, as well as burning at a lower temperature. These engines need a volume of hot air, hot enough for the temperature differential to allow substantial volume change, but the volume of the hot air must essentially fill the cylinder by the time the port closes, and having a hotter flame with less volume does not accomplish this, as tested with several small butane torches, requiring a "soft flame", as John has said, to provide the volume of hot gasses.
I would also note, what Nick said about the cam closing the valve, and allowing the spring to open it when the vacuum allows, has been a major factor in the better performance of the oddball, which has been my test piece. I also note that when I take my Duclos flame sucker, and set it up, brass cylinder, bronze piston, bronze valve, with the tip of the flame just a quarter of an inch from the port when cold, and give it a good spin, if I keep that red, meaning fully burned, no unburned fuel left, as in the blue part, so it is almost exclusively pulled into the port, it will come up to about half speed immediately and if I carefully maintain that tip just going in, while the rest of the flame goes across the valve, pulling it further away as it speeds up, I get no condensation, no popping, and it goes from half speed up to full speed in about thirty seconds of running, and will continue at that speed until the graphite pencil rubbings are gone and it sticks, some fifteen minutes or so.
The Duclos works well this way, but the oddball is arranged such that it doesn't have as much flame for its volume, and I can't get just the top of the flame going in, as I do with the Duclos. I believe the designer of the "poppin" was right in his putting a thin edge on the port, to minimize temperature change there, as my head is almost a quarter inch thick, and takes some time before it quits sweating moisture. If I fail with the Duclos, and get too much flame in say twice, it will require being spun over until warm before it will start off, and will pop, showing the valve is sticking due to the moisture wicking between it and the cylinder. I would suggest that is where your engine is popping or quacking, John, as the cooled air is forced out against valve pressure, causing the valve to act as a reed, even as a block of graphite. I suspect engines that are closer to "square" are more efficient as well, as long strokes mean lots of contact area between pistons and cylinders. I've reached the point with the oddball, where the valve timing is controlling the speed, and its opening is controlled by the vacuum holding the reed until the pressure equalizes, and it is almost silent once it is hot and running at about six hundred rpm. I appreciate all the chiming in, lots of good ideas to consider. Cheers, Jack