[Bruce]

For up/down thrust:
- trim the plane for straight & level flight at power
- make a horizontal pass at power and then chop the throttle
- without power, the plane will respond to the trim you put in to overcome any uneven up/down thrust. For example, if you have too much up thrust in the motor, you had to put in down trim to overcome it and achieve level flight. So, in this example, when you cut power, the plane will desend quickly telling you that you need to reduce the up thrust in the motor. If the thrust is close to correct, when you chop power the plane should continue level for a bit and then desend in a smooth arc that you would expect with loss of speed. Too much down thrust is simply the reverse of this example.
- Adjust by shimming the motor in the appropriate direction and try again.

This, like most trimming issues, is a compromise. What you are after is minimizing up/down variation with throttle changes for the style/speed/plane you fly.