OK, looks like we've finally got things working now. I had my best friend Dave take a look and he was concerned about some "flex" in my throttle linkage. I got rid of that problem and then let him tweak the carb needles for me. I think he was right that the flex in my pushrods was stopping me from getting any consistent readings from my engine. Once that was eliminated, it was really a matter of going by the numbers until we got it running right.
Now the engine is idling (with the cowl on) quite consistently at about 1600 RPMs... with an idle-down setting that runs pretty reliably at about 1350-1400 RPMs. Transitions are very good and I'm running the top end a little rich at 6600 RPMs. It can peak at just over 6800 right now, so I'm going to leave it at 6600 for the first couple gallons, then lean up the high end later.
So far so good... hopefully nothing will change when I take it to the field... you know how those RC gremlins are!
Tom