[wizard]

Here are a couple of things to check. Lateral balance. Lift the plane by the prop and rudder, if one wing tip drops every time, it is heavy. Add weight to the other wing tip. There are some very good threads on trimming you plane on the site. Just do a thread search on trimming.

The other possibility is that your elevator halves are not moving the same distance. Tape a piece of carbon fiber rod, or popsicle stick to each rudder half and have the tips just about touching. Slowly work the elevator through the entire range of travel and insure that they are moving together.

This is just a couple of ideas but might get you started, on finding the problem.