Many trainers that come with lighter engines, like the OS, LA's tend to have this problem. The first thing to do is to put the battery pack under or over the fuel tank, as far forward as possible. Wrapped well in foam and rubber band the foam in place. You can also do new servo trays and move all of the servos as far forward as possible. Depending on what type of elevator and rudder controls you have, you can go to pull/pull on the rudder with very light weight metal cable and use Sullivan golden rod push rods (all light plastic). For every ounce you get out of the tail you need about three or four ounces less on the nose. Moving the engine forward some will also help, so take the easiest things to do first and keep checking as you go. I just took over two pounds out of my 33% Extra (from 25 pounds down to 23 pounds) what a difference. The absolute last thing you want to do is to add weight. The lighter the wing loading, the better it flies and responds.

Hope this helps, any questions you can email me at [email protected]