Well, part of the poor running at wide open mystery has been revealed. One carb was certainly running much richer than the other. After another round with the carb balancer, I decided to swith the floats just to see what would happen. While pulling out the float from the richer carb, I noticed that it had managed to develop fluid inside. Shaking it produced the unmistakable sound of fluid sloshing around. Not a lot, but apparently enough. I had seen small leaks develop before that let gas in, but there was no apparent leak, and even leaving it out for days while I waited on a new float produced no discernible change !! Not the slightest scent of gasoline, no difference in the amount of fluid. Even the weight was about the same. It is obviously condensation, but this was a first. Next I will apply some heat......Meanwhile, a brand new shiny float showed up and was installed. I opted to stay with the more expensive brass float rather than the plastic alternative.