Dave,
Thanks for the suggestion, the little K&B .21 were the last of the .21 run and were built specifically (timed) for R/C Combat they are considerably higher performance that the "normal" .21 however this is the first one I have tried with a 1/4 pipe. I am sure it will respond some what to the pipe. I also have 5 or 6 of these little powerhouses (2 NIB) from when I was flying SCALE R/C combat (2000 class 2105 national points champion) the carb throat is about the dia of most .40's. I hope to fly before the weather chases me inside here in the Midwest. I was in Toronto last Thursday night really lousy weather but at least it was above freezing.
Sparky