I found two older post, over at RR, that describe the same problem that I'm having. The term,they used,was 4 cycling, meaning the engine is changing, back & forth from 2 to 4 cycle, thus causing the tail twitch.With my TT50, you can clearly hear the tone changing back and forth. The cause given, for the problem was improper engine tuning. One guy said he fixed the problem by slowly leaning out his high speed needle, until
the 4 cycling stopped. I'm thinking that I'm running my high speed richer than most, according to other post I've read, so I'm going to try slowly leaning out my high speed, and see what happens.
Mike