I have a .46 SF (predecessor to the FX) in mine because I use it as a practice plane at the begging of the season before flying my pattern and warbird ships. This engine is twice the power the Eagle needs. Adding a washer to decrease the downthrust will help having to compensate with elevator trim if you want to run at full throttle (thats what I did, so I can re-adust it when I use it to train new pilots). Be careful though, because the plane will pitch down more at slower speeds. The downthrust is designed for the Eagle to stay level at slow training speeds. If you are still learning, it is better to put a stop on your throttle that prevents you from going full throttle. Your Eagle should maintain the proper attitude.

You can also try a less pitch prop.

If no matter what you do, it still climbs, then check the incidence of the horizontal stab and also, like was said before, the CG. The .46 FX, although beefier, is lighter than the older K&B's Fox's, and VECO's that the Eagle was designed around. I had to add 4 oz to the nose of mine with the older SF.

Regards,
Scott