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Helping keep British Motorcycles on the road for over 30 years - established 1977

Ernie Bransden, the owner and brains behind Boyer ignitions, offers the following suggestions to diagnose problems with a bike fitted with an electronic ignition…


BATTERY HAS POWER?: Switch on headlamp and activate stop lamp. They should stay bright for more than one minute.

THE FUSE KEEPS BLOWING: Replace the fuse with a 21 watt indicator bulb. As the individual electrical circuits are switched on, the bulb will glow dimly, if a faulty circuit is connected, the bulb will glow brightly. If the bulb glows brightly with nothing switched on, remove wires from components in turn until the bulb goes out; the last one removed will be the faulty circuit.

IGNITION UNIT HAS POWER?: Using a bulb or voltmeter check the main power feed to the ignition unit. This would be the wire from the ignition or kill switch. With bulb connected between the ignition feed wire at the ignition box and battery ground, the bulb should glow brightly. If dim or varying, try moving the fuse holder, wiring, handlebars, to locate any faulty connection.

Then test between the ignition feed wire at the box and the wire used to ground or earth the ignition system. If the bulb glowed brightly when connected between the feed wire and battery ground system, but is dim when connected between the ignition feed wire and the wire used to ground the ignition, you have a faulty ground. (The bulb draws similar current to the ignition and is a more useful test than the voltmeter only.) Poor earth connections are hard to locate.

THE UNIT HAS POWER – SPARKS ON SWITCHING ON AND OFF: Most early MKIII (not Micro-MKIII, Micro-Digital or Micro-Power which will not spark when turned on and off) ignition units will produce a spark on switching on and off; if this is so and sparks are produced on all cylinders then the ignition coils must be in good order. If one or more fail to spark, a coil could be faulty. On four cylinder machines try disconnecting one coil at a time, and switching on and off, checking for sparks. On other machines that use more than one coil in series one coil failing can stop sparking due to coil failure and cause all the coils not to spark.. Also one coil can have an internal short to ground, and while it will fire, it can cause the coils after it in the chain (which are in good working order) to stop working. This is very common when a Lucas/PVL coils that are overtightened in the metal clamp. The case becomes crushed and touches the windings inside. This can occur when the coil warms up. The Micro-MKIII, Micro-Digital and Micro-Power units all turn off when not being triggered, therefore, it is best to carry out the next test as you may not always have a spark on turning on and off.

THE UNIT HAS POWER – NO SPARKS ON SWITCHING ON AND OFF AND NO SPARKS WHEN CRANKING: After performing the bulb test above to ensure the box has power, disconnect the wires from the ignition box that go to the pickup trigger plate. With the ignition on, touch these two wires together. Making and breaking the connection should make a spark at the spark plugs. If no spark is present then the ignition box is most likely (see checking coils above) faulty. The only units that will not trigger in this way are the racing crank triggered Digital and Norton rotary units (A rapid tap on the end of the pickup will induce the ignition to fire. A single tap will arm the ignition, but if it does not see additional signals after a few seconds will turn off the box and inadvertently fire the coil). Check that the rotor magnets are running within the two metal pole pieces on the trigger plate. On British machines it is possible to move the rotor out slightly by placing a thin metal shim around the taper. The ignition will not fire by hand at less than 200 rpm.

CHECKING THE PICKUP PLATE: A full visual check of the condition of the circuit board and coils looking for loose or broken parts. Check for signs of the rotor touching the solder connections. Using a multimeter check the resistance of each pickup coil (should be approx. 65 ohms or 130 ohms across the two coils) and the total resistance across the wires or terminals. With the meter still attached, run your fingers around the coils, if the resistance changes there could be a broken winding inside. Attach the meter across the trigger plate’s wires and pull on them. If the resistance changes you could have a broken wire.

CHECKING THE ROTOR: The magnets on the Boyer ignition rotor should just hold the weight of the rotor when placed against a piece of steel. Check the marking spots are the same way around. All magnets should have a similar amount of strength.

SPARKS ON CRANKING BUT WON’T FIRE: Check the pickup wires do not change colour in the wiring loom, as swapping these will make the ignition fire over 50 degrees retarded. With the digital system, check that you have suppressed plug caps fitted of approx. 5,000 ohm. If timing has just been done, don ‘t forget that the timing angle on the camshaft is half of the crankshaft’s (i.e. on a 650 Triumph full advance timing is 38 degrees but is set at 19 degrees on the camshaft.)

CONTINUOUS SPARKING WITHOUT CRANKING THE ENGINE: A poor battery with a battery charger connected or one or more bad cells in the battery. A high resistance in the wiring circuit or earth return. Check that the engine is earthed back to the frame and battery circuit. Plastic (powder coated) frames must have a good earth connection to the engine case and battery. A wrong type of ignition coil with a very low primary resistance (under 2 to 3 ohms) will draw a very high current and produce a large volt drop across the wiring. All these will keep turning the ignition on and off, generating a chain of sparks.

ENGINE RUNS FAST AT IDLE AND KICKS BACK ON STARTING. Poor fuse connection, battery running low or variable voltage to the ignition. As the alternator charges the system with increasing engine speed the problem can clear. But as the engine speed decreases the system voltage drops and the problem reappears as the motor returns to idle.

ENGINE RUNS (POOR STARTING), BUT MISFIRES: Poor connection at rivet attaching terminal of ignition switch or bad connection vibrating on and off. Also suppressor plug caps with open (internally broken) circuit.

(Thanks to John at T.I.O.C. for the above information)

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