The centering spring adjustment requires removing the mouthpiece, lip button, front cover (four screws), and the joystick gimbal. The adjustment screws are on the back of the gimbal. A 1.5 mm hex wrench is used to adjust them. There are several fragile wires and tubes in-between the gimbal and the circuit board that need to be in the right places. Observe their positions before lifting the gimbal off the four standoffs.
The "strong" setting has the spring stretched to the maximum distance. The light setting is about half-way. Turn the set screw counter-clockwise to increase the tension. Clockwise to lighten the tension.
When replacing the gimbal on the four metal standoffs, ensure the wires can freely move when the gimbal is moved up and down, and that the tubing is not pinched.