Manual - Chapter 6 - Ignition system

10. Ignition timing: adjusting

  1. Setting the ignition timing requires the use not only of a dial gauge with the necessary long adaptors but also a device which will indicate precisely when the trigger assembly sends a pulse to the control unit. BMW recommend a service tool 12 3 650 which is used with a test lead 12 3 651; with this equipment an LED lights when the trigger assembly reaches the firing point. Since it is expensive and not likely to be required very often, this equipment places the task beyond the scope of most owners.
  2. Accordingly, owners are advised to take their machine to an authorised BMW dealer for the work to be carried out. For those who have the equipment. proceed as follows.
  3. Note: Before starting work refer to Section 2 of this Chapter and take all the necessary precautions to prevent any risk of damage or of personal injury.
  4. On 75 models the ignition timing is set on number 3 (ie the rearmost) cylinder; on 100 models it is set on number 1 (ie the front) cylinder. Remove the spark plugs (see Maintenance - Major Service - Renew the spark plugs), install the dial gauge on the appropriate cylinder, and zero it at Top Dead Centre (TDC).
  5. Remove the fuel tank. See Chapter 5. Disconnect the trigger assembly wires at the connector on the frame top tubes and connect the test lead and ignition tester. Remove the trigger assembly front cover
  6. Turn the crankshaft backwards (ie clockwise, looking at the ignition trigger) to a point just before the specified firing point then slowly rotate it forwards again until the piston is exactly at the specified distance before TDC, whereupon the ignition tester diode should light. If not, slacken the trigger backplate mounting Allen screws and rotate the plate anticlockwise to retard the timing or clockwise to advance it. When the diode lights at the correct moment, tighten the backplate screws.
  7. Repeat the procedure to check that the setting is correct, then disconnect the test equipment and refit all disturbed components.