Tech. 6


Article supplied by Peter Lawrence on trouble shooting the Boyer Bransden Ignition system

This system normally produces very good quality bright blue sparks at the plugs, due to the combination of the high quality modern design of ignition coil and the ignition unit, which is matched to it. The most likely cause of weak sparks is a poor 12-volt supply to the ignition unit & coil. This could be a bad electrical connection, poor switch contacts, bad earth or discharged/faulty battery. You can connect the positive terminal of the ignition coil directly to the battery positive (preferably via an 8amp fuse), no relay required. The ignition switch would then feed +12 volts to just the ignition only (red wire). Wiring the ignition this way helps overcome poor switches / poor connections, but it is preferable to trace the problem and rectify it.

After fitting electronic ignition it is not uncommon to experience a slight increase in idle speed due to improved combustion. Adjusting the idle setting on the carburettor(s) should rectify this. 

The working voltage range for our ignition units is 10 to 16 volts. The ignition coil is switched with high current pulses (approx. 6 amps) for a short period; the average current draw is approx. 1 amp. The static current (engine not running) is approx. 40mA. 

We hope that the above information is of help in solving running problems,

Yours sincerely, 

Technical Dept.

Boyer Bransden Electronics Ltd.



BATTERY HAS POWER.  (Switch on headlamp, this should stay bright for one minute) 

THE FUSE KEEPS BLOWING.  Replace the fuse with a 21 watt indicator bulb. As the 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 bright with nothing switched on, remove wires from components in turn until the bulb goes out, the last one removed will be the area of the faulty circuit. 

IGNITION UNIT HAS POWER.  Using a bulb or voltmeter check the main power feed in to the ignition unit. This would be the wire from the ignition switch or kill switch.  A 21 watt indicator bulb with wires attached makes a very good test lamp. With this connected between the frame and ignition feed wire, the lamp should glow brightly, if dim or varying try moving the fuse holder, wiring, handlebars, to locate any faulty connections. Also test between the feed wire and the wire used to ground or earth the system, as a poor earth connection can be most difficult to find.  The bulb draws similar current to the ignition and is a more useful test than the voltmeter only. 

THE UNIT HAS POWER   Most MKlll 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 the coils are used singularly or connected in a chain in series.  One coil failing can stop sparking but if it becomes short circuit to its case the coils after it in the chain will stop working. It is possible that a working coil is shorting to case, and stopping the other coils in the chain from working. This is very common when a Lucas coil is over tightened 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. 

SPARKS ON SWITCHING ON & OFF   but not on cranking.  Disconnect the wires from the ignition box that go to the stator plate. With the ignition on, touch these two wires together ,making and breaking should produce a spark at the sparkplugs. If sparks are present then the ignition box is most likely to be in good order, if none are present the box is faulty. The only units that will not trigger in this way are the racing crank triggered Digital, and Norton rotary unit.  Check that the rotor magnets are running within the two metal pole pieces. On British machines, if necessary the rotor can be moved out slightly by placing a thin metal shim around the taper. The ignition will not fire if turned by hand at less than 200 RPM.

 CHECKING THE STATOR 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 and then the total resistance across the wires or terminal With the meter still connected, run your fingers round the coils, if the resistance changes there could be a broken winding inside. 

CHECKING THE ROTOR..   The magnets should just hold the weight of the rotor when placed against apiece of steel.  Check the marking spots are the same way round. All magnets should have a similar amount of strength. 

SPARKS ON CRANKING BUT WON'T FIRE.   Check the stator wires do not change colour in the wiring loom, as swapping these will make the ignition fire over 50 degrees retarded.   With a digital system check you have suppressed plug caps fitted of approx. 5,000 ohms.   lf timing has just been done, don't forget that the timing angle on the camshaft is half of the crankshafts (ie on a 650 Triumph full advance timing is 38 degrees crankshaft 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 coated frames must have a good earth return to the engine case. A wrong type of ignition coil with a very low primary resistance, this will draw a very high current and produce a large volt drop across the wiring. The unit will keep turning on and off generating a chain of sparks.

 ENGINE RUNS FAST AT IDLE ,KICKS BACK ON STARTING.    Poor fuse connection or wiring running low or variable voltage to the ignition. As the alternator charges into the system with increasing speed the problem canclear.

 ENGINE RUNS(POOR STARTING) BUT MISFIRES.   Poor ignition switch or bad connection vibrating on and off.  Spark plug caps open circuit (suppressors broken up).

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