SETTING THE MAGNETO
Because the magneto has a low supply voltage when starting the motorcycle, it is important to setup the magneto right. The points should open at the most effective moment. In practice that is luckily quite easy. For them who want to read more about the details, have a look at "abrisz". The magnet that is attached to the camshaft is marked. Also the magneto baseplate has a mark, a small notch in the top edge of the brass plate. When the S-mark on the flywheel is in the middle of the inspection hole, these two magneto marks should line up. It is a little difficult to see. Looking from the side you get too much deviation. Usually I lay down on the floor, peeking from below. Then I feel the two marks with a small screwdriver. If the screwdriver sticks out perpendicular to the brass plate, it's okay. On some models you can see it between the horn and the front fender.
When the marks are a little bit out of line, you can loosen the two M6 screws that hold down the magneto body, and turn the body. When the error is very big, you will have to rotate the magnet. The magnet has a non-indexed taper fit on the camshaft. That means that you can loosen the magnet, turn it in the right position and retighten it again. Have a look at
tools to see how you can loosen the magnet.Next you set the points opening width. Turn the engine until the points are opened maximal, and set the points width to about 0.4 mm. Always set the points width first, before you set the timing, because changing the width, also alters the timing.
A common mistake in the BMW world is to set the timing by turning the magneto body around. They loosen the M6 bolts, then point a stroboscope at the timing marks on the flywheel, and turn the body until the S-mark is in the middle of the inspection window. All very convenient, but with this method you throw away the abrisz setting that you made some paragraphs before. The proper way for setting the ignition timing is to remove the centrifugal advance unit, loosen the two screws that hold the pointsplate, turn it a little, reattach the advance unit, check the timing again, etc. You can turn the pointsplate without interfering with the pointswidth or the abrisz setting. Because this is a little inconvenient, there is a special pointsplate available that replaces the whole brassplate, and which makes it possible to change the ignition timing directly.
For checking the ignition timing I recomment to use a stroboscope. Direct the beam of the stroboscope at the inspection port, and you will see an image of the S-mark, which should be in the middle. When you use the static timing method, don't send a big current through the primairy coil, because that can impair the magnetic strength. So either use a buzzer or testlamp with a small battery or disconnect the wire from the points to the coil.