No joy yet. The strongest spring does work all right (near as I can tell.) I had the engine running for short duration blasts, and grabbed the video camera a dozen different times but the engine wouldn't oblige me by staying running. I played with the ignition timing, first advancing it, then retarding it, looking for the "sweet spot" but never found it. I adjusted the carburetor needle to every conceivable position, but the best run I got was only about a two minute duration, with the engine gradually slowing down and coming to a stop. After about 50 different attempts to start the engine, I was rewarded with a rather ominous "clanking" sound every time it started. Nothing was visibly wrong that could be seen from outside the engine (and almost everything is on the outside of the engine.) The compression has improved exponentially, so the pressure caused by the engine firing has firmly seated the valves. I never reached the point where the engine "took off" and gained rpm until the centrifugal governor was activated, but I was able to activate it by spinning the engine fast enough with my 3/8" variable speed drill, so I know the centrifugal governor is working. I will pull the head off the engine sometime today and make sure that the piston isn't coming adrift from the connecting rod, and ascertain that my pressed together crankshaft hasn't slipped out of alignment.
The next engine will be double acting oscillating engine? 
