Couple poppop threads here at rcgroups:
To expand on the boiler-angle-is-bad comment I made: The angle sends liquid water to the low point of the boiler, naturally. The location of the tubes at the low point allows the water to be expelled on the first pop. If the boiler were level, the water would not pool at the tubes. Or, if the tubes were moved away from the low point, or simply stuck up through the floor of the boiler so they did not act like funnels, then my hypothesis problem would be solved.
Solutions: Moving the tubes would be hard, I think. But, depending on how hard it is to break the tube-transom seal, you might be able to level the boiler just by sliding all the tubes aft. This would lower the boiler, so you'd have to adjust the wick lengths of your burner, of course. For testing, a short stub of birthday candle would serve as a quick and easy burner.
Ooyah, I've seen Daryl Canada's videos, they are neat and he is an Expert. But I lost my downloads of the videos in a computer crash, so thanks for posting :-).
Building the diaphram style boiler appears to be an art: A friend built 2 seemingly identical boilers - one ran like the dickens, one was a complete dud. So, persistence is required to succeed with pop-pops, I conclude *smiles*.