Listen to DMcQuinn and use the downthrust. The original Seniors were intended to use a full 5 degrees downthrust and if omitted even slight power changes resulted in substantial pitch trim changes with every little power change. The seniors are wonderful airplanes and a pleasure to fly when set up properly. Pitch trim changes with power are always a function of how far away the thrustline is, either above or below the aerodynamic center of the aircraft. The further it is below (as in a deep bellied cabin type such as the Senior) the more pronounced the pitch trim changes with power change. A seaplane with an overhead pylon mounted engine will respond exactly the opposite and pitch down with application of power. An airplane that pitchs up with power is not neccessarily indicative of a nose heavy airplane. Use the downthrust.

Look at the Cadet Senior in my avitar it only has two degrees of down thrust and has no pitch change with power but that is only because the engines thrustlines are raised up a full four inchs from the stock single engine Cadet in wing nacelles and the thrust lines are very close to the aerodynamic center.

John