Why not simply bend the float rod downward (if signalling too soon) or upward (otherwise)?
Because bending the arm changes the relative position of the wiper on the fuel level resistor to which the arm is connected, affecting the reading on the fuel gauge (if the bike is equipped with one). Altering the contact point for the low fuel indicator using the BMW-provided adjustment wheel does not upset the fuel level sender. Why "McGiver" it if you can do it properly?
The adjustment process is easy:
1. Take out the sender and set it up on the bench so that the float ball just touches the table top in its resting position. Fix the sender's base.
2. Use an ohmmeter to measure resistance between White and Brown wires
3. Lift the float arm until the ohmmeter goes from 0 ohms to open circuit. Measure the height of the float ball above the bench top.
4. Adjust the toothed wheel to add or subtract from the reserve volume as you desire.
5. Perform Step #3 again, noting the new height the float assumes when conductivity ceases -- higher above the bench for more reserve volume or lower to the bench for less reserve volume.
