I agree Steve that the servo needs to be centered, otherwise the bellcrank system, which I have had to do once or twice. Another answer on some planes that I have done a lot is to "step" the two servos.....elevator servo with the pushrod centered in the fuselage, and, looking down into the cavity (low wing), the rudder servo is in front and "higher" (i.e. cables are below the elevator pushrod if the plane is right side up) with the cables running over the elevator servo and pushrod. Hope this makes sense......written as though you are looking down into the radio cavity of a low-wing airplane with the fuselage upside down.

Clair