Originally posted by BotleRocketWar
You were most likely experiencing slipstream... P-Factor is a very minor effect. Even during take-off your AOA is not high enough with an Extra for p-factor to make that much of a difference. Slow speeds and high power settings is when slipstream is most pronounced.
I guess there is no way to know, huh? 
Well, if the tail came up fast and oscillated it would yaw right left as the tail oscillated from center.
With the 12-6 you would see it do the first left turn+climb with the nose way out on the outside of the turn. Lots of drag. Right turns much easier. Probably made much more significant as it was set up tail heavy. The 11-7 was much easier to fly. Then again, the change from the 61FX to 91FX changed the takeoff completly. Roll a bit then straight up.
The plane was a bit under powered with the 61FX and the crappy pitts muffler. That made climb out slow.
Moot point as I flew the plane until it totalled itself. Guess the rudder had too much "Hanger rash" over the years.
My new GP PW Extra has little P-effect. Then again takeoff is again vertical.