Adjusting the charge voltage

Duane Ausherman

Many of the factory delivered /5 bikes had the charge voltage adjusted well below 14 Volts. We found that it had to be above 14, and our goal was to fix it by adjusting the voltage regulator. The factory never published a procedure for this fix. The BMW solution was to offer a list of things the rider was doing wrong.

Have the motorcycle warmed up.
Remove the tank.
Under the tank is a metal box on the right forward area fastened to the frame with 2 bolts. You will remove the metal box 2 1/2″ wide, 2 1/2″ high, and 1 1/2″ deep.
Unplug the wires and remove the two bolts.
Remove the tape from around the bottom edge. This tape seals out water.
Clamp it in a vise and use a flat screwdriver. Place the screwdriver facing upwards in the seam and gently tap the screwdriver upwards.
Now you have something that should look like this photo.
I used a pen as a pointer to direct you to the place that you will adjust. See that oddly shaped piece of sheet metal? Just above it is a thin flat spring. You will use needle nose pliers to bend the sheet metal up a bit. This increases the upward pressure on the spring.
However, before you do any bending, mount it back on the bike and plug in the wires.
Rig up a way to mount the tank above the motorcycle in order to feed fuel into the carbs. Have a fire extinguisher at the ready, just in case.
Have your digital voltmeter leads directly on the battery posts.
Start the motorcycle, turn on the headlight and take it up to around 3000 rpm. Keep the engine running until the voltage reading is stable. This is your current charge voltage.
Gently bend the tab upwards or downwards under the sheet metal spring. You will see the voltage rise or fall. Keep bending until you get to 14.1 volts. If you only ride very short distances, say 5 miles to work and then back home later, set it at 14.2 volts.
Electronic regulators are available today that may be better for your application.

Updated 17 July 2022