Originally Posted by franklin_m

...Why is all this important? Because what we see is that every force on the aircraft at this point would predict a nose LEFT yaw as the engine speed increases, the aircraft starts rolling, and the nose pitches down. However, your aircraft is demonstrating the opposite behavior. So where to start?

Check the amount of right thrust built in?
Under static conditions, is the tail wheel parallel to the aircraft longitudinal axis (emphasis added)?
Under static conditions, are the main wheels parallel to the aircraft longitudinal axis?
Do these remain parallel under dynamic conditions? (i.e. no struts bend under loads as throttle comes up) (emphasis added)
Is the angle from the aircraft CG through the main wheel axles approximately 15 degrees forward of vertical axis per recommendation in note 3?
Is tail-wheel direction parallel with the longitudinal axis when rudder is neutral (emphasis added)?
Does the tail wheel stay aligned with the rudder under load (emphasis added)?
Check control surface rigging. For example, is there some built in right yaw input (tailwheel or rudder)?