Lucas Service Information

Location and Remedy of Faults

Although every precaution is taken to ensure trouble-free running, electrical faults may sometimes arise and the following test procedure is recommended.

When checking the continuity of circuits, a flashlamp battery and bulb should be used. Do not "flash" the end of a live cable to earth, as this may cause heavy currents which damage the equipment. If a vehicle battery is to be used, a low wattage bulb of similar voltage must be connected in series with the circuit to be checked. Never check the continuity of alternator stator windings when the rotor is in position. The rotor should be removed to avoid demagnetisation and reduced output.

Battery Charging Systems

Engine will not start on IGN position:

  1. Turn the switch to EMG position if provided. If the engine now starts, the battery is probably discharged. If there is no EMG position, check the condition of the battery and recharge, if necessary.
  2. Remove the H.T. cable from the sparking plug and hold the cable end about 1/8" from a metal part of the engine while the fatter is turned over. If sparks occur regularly, the ignition system is functioning correctly. Check for engine defects after examining the sparking plug.
  3. If sparks do not occur in test (2), check for a fault in the low tension circuit. Check the wiring from battery to fuse, switch, coil and contact breaker. If the circuit is continuous, examine the contact breaker and if necessary clean and adjust the contacts. Also, check the engine timing.

Engine will not start on EMG position:

Carry out previous tests (2) and (3), check that the alternator rotor is the correct way round on the engine shaft (the name "Lucas" should face away from the engine).

Engine misfires:

  1. Examine the contact breaker. If necessary, clean the contacts and adjust the gap.
  2. Remove the sparking plug (or each plug in turn), rest it on the cylinder head and observe if a spark occurs at the plug points when the engine is turned. Irregular sparking may be due to dirty plugs (which may be cleaned and adjusted) or to defective high tension cables. If the insulation of any cable shows signs of deterioration or cracking it should be renewed.
  3. If sparking is regular at each plug when tested as described in (2), the trouble is probably due to engine defects, and the carburetter, petrol supply, etc., must be examined.
  4. If misfiring occurs after the engine has been running for some time, check that the ignition switch is in the normal IGN position. If run continuously in the EMG position, the rising voltage of the battery may eventually cause misfiring to occur.
A.C. Ignition


  1. Keep the contact breaker clean and ensure the maximum opening is set at 0.014'- 00l6'.
  2. Keep the sparking plug electrodes clean and correctly set.
  3. Keep to the manufacturer's timing instructions.

Engine will not start or misfires:

  1. Remove the H.T. cable from the sparking plug and hold the cable end about 18' (3 mm) from the cylinder block. Sparks should jump this gap regularly when the engine is turned at kick-start speed.
  2. If sparks are obtained, check the sparking plug, reset and clean, or renew as necessary.
  3. If no sparks are obtained, inspect the H.T. cable and renew, as necessary. Check contact breaker gap setting.
  4. If the sparking plug, H.T. cable and contact breaker gap setting are satisfactory, check for engine defects, faulty fuel supply, etc.

Charging Equipment Battery in low state of charge:

  1. This will be indicated by poor or no lights when the engine is stationary, and varying light intensity when the engine is running.
  2. Check the condition of the battery, and recharge if necessary.
  3. Check the wiring from the battery to switch, rectifier, and alternator. Ensure all connections are clean and tight.

Excessive circuit voltage:

  1. This will be indicated by burnt out or blackened bulbs and possibly burned ignition contacts.
  2. Examine the wiring for loose or broken connections.
  3. Check the earth connections to the battery, rectifier and Zener diode.
  4. Examine the battery, checking the electrolyte level and removing any corrosion.

Lighting Equipment Failure of lights:

  1. If one bulb fails to light, replace with a new bulb.
  2. If all lamps fail to light, check the fuse (if fitted) and check the battery condition, recharging if necessary.
  3. Examine the circuitry and replace broken or loose connections.

Lights fade when switched on:

  • Check the battery condition, and recharge if necessary.

Brilliance varies with engine speed:

  • Check the battery condition, and recharge if necessary.

Lights flicker:

  • Examine the wiring for loose connections or damaged cable insulation. Check the battery condition.

Headlamp illumination insufficient:

  1. If the bulb is discoloured or filaments have sagged as a result of long service, replace with a new bulb of the same type.
  2. Check the setting of the lamp and the condition of the reflector.
Lucas Service Information
Joseph Lucas (Sales & Service) LTD.

British Only Motorcycles And Parts, Inc.
32451 Park Lane
Garden City, Michigan 48135 USA
Phone: 734-421-0303
Fax: 734-422-9253

Order Desk:

1-800-BRT-ONLY or 1-800-278-6659


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