Hi there!
Here are some advice I have picked up by reading this Forum:

- Some servos are very sensitive to operate with a Y-harness with the the problems you describe. However, since you are using them as elevons they must be plugged in to separate channels of your Rx so this can't be the problem.

- Make sure you are using the full travel of the servo to obtain the recommended throw of the control surface. By moving the link one step in to the center of the servo you may reduce the problems you have (because you are reducing the speed and acceleration of the control surface).

- If you currently are running on 5-cell Rx batteries you could try with a 4-cell pack. This will reduce the speed slightly of the servo and probably reduce the occilaton.

- If you have a Tx where you can adjust the servo speed you should have a go at it. Reduce the speed step by step and se what happens. I think there is a good chance it will solve the problem. In my oppinion you don't really need a quick servo for a Jet-model that is supposed to fly smooth and gentle.

- Yes, mass balancing will help and you don't necessary have to get 100% static balance. Take some large coins and attach them temporarely with tape close to the leading edge close to the fuse of the elevons. I'll bet it will reduce the occilation or eliminate it completely.

- Very true you have to get rid of all potential slope in the linkages.

Good luck /Johan