If You use a electronic ignition system watch out for the
If the Zener Diode is badly grounded or have worn out,
it could give more than 20 Volt!!, and make the electronic
system to set the ignition timing too high with the result of a hole
in the piston.
How to Check your Zener Diode.
Contact Breaker & Spark Plug.
The correct gap on Contact Braker is .015 in (.381 mm)
Spark timing, degrees fully advanced: 30
Spark plug: N4 ( MX N3 )
Maintenance and testing
The rectifier is a silicon semi-conductor device
which allows currellt to flow in one direction
only. lt is connected to provide full-wave rectification
of alternator output Current.
The rectifier requires no maintenance beyond checking
that the connections are clean and tight.
The nuts clamping the rectifier plates together
must not under any circumstances be slackened.
A separate nut is used to secure the rectifier and
it is important to check periodically that the
rectifier is firmly attached andI therefore well
When tightening the rectifier securing nut, hold
the rectifier with a second spanner, for if the
plates are twisted, the internal
connections will be broken.
Testing the rectifier on the machine
(1) Disconnnect the Zener Diode by removing
the straight Lucar connector with the Brown/
Blue cable from the 2 MC capacitor.
(2) Locate the snap connector junction for the
Brown/Blue cable to the box and disconnect.
(3) Connect a D.C. voltmeter (with the 1 ohm
load in parallel) with the red lead to earth
and the Black lead to the Brown/Blue cable
from the box.
(4) Locate the White/Yellow cable in the other
snap connector junction from the box. and
using a jumper lead connect the cable from
the box to the negative (-) terminal of the
(5) Start the machine and run at approximately
3.000 rev./min., and take a reading from the
voltmeter. This should not read less than
7. 75 volts, which indicates the rectifier is
operating satisfactorily. A lower reading
indicates a fault in the rectifier which can be
confirmed by a bench test.
(6) Stop engine before disconnecting the voltmeter.
2 MC ELECTROLYTIC CAPACITOR
The capacitor is an electrolytic polarised unit,
which will be irreparably damaged if incorrectly
Looking at the terminal end of the unit, two
Lucar terminals of different sizes will be observed,
the small terminal being the positive earth terminal
: for identitication the rivet has a red
The double Lucar terminal is the negative
The basic object of using the electrolytic
capacitor in the system is to enable the motorcycle
to be run without a battery giving the rider
the advantage of using the machine for competition work.
and refittilng the battery for normal
If the battery should be disconnected and the
machine run on capacitor ensure that the negative
(brown/blue) lead is well insullated.
Disconnect the battery. Start and run the
engine. Full lighting should be available.
If engine will not fire and run.
Proceed to next check.
(l) Disconnect the capacitor.
(2) Connect the capacitor direct to a 12 volt
battery for 5 seconds (see polarity note).
(3) Disconnect the battery and let the charged
capacitor stand for 5 minutes.
(4) Connect a D.C. voltmeter across the terminals (see polarity note) and note the
steady reading after the initial swing, which
should not be less than 9 volts for a serviceable unit.
The Zener diode is mounted within the electrical box at the front.
Providing the diode is kept clean, to ensure
maximum efficiency, no maintenance will be
The "earthing" stud which secures the diode
must not be subjected to a tightening torque
greater than 24 - 28 lb./in. The electrical box
lid acts as a heat sink and it is most important
that the diode makes good contact with the
Checking performance of the Zener Diode
The battery should be fully charged before
starting. If there is any doubt about the state of
charge of the battery, it should be recharged
before commencing the test.
Isolate the Zener Diode by disconnecting all
leads from the 2MC capacitor.
Connect a D.C. voltmeter Black lead to the
straight Lucar with the Brown/Blue cable and
the voltmeter Red lead to earth.
Connect a D.C. ammeter Red lead to the straight Lucar
with the Brown/Blue cable, and the Black lead
to the right angle Lucar with a Brown/Blue
Check that all electrical equipment other
than the ignition is switched off.
Start the engine and raise r.p.m. to approximately 3.000.
Take a careful note of the readings.
As the system voltage rises to 12.75 volts no
reading should occur on the ammeter.
The voltage will then continue to rise and after 12.75
volts the ammeter should start to read.
The next check occurs when the ammeter rises to 2
amps, at this point the voltmeter should read
between 13.5 and 15.5 volts.
The Zener Diode must be replaced if:-
(1) Current flow commences before 12.75 V is
(2) Voltmeter registers more than 15.5 V.
before 2 amps is shown on the ammeter.
Electric drawing 96 kb in pdf file (original)
Electric drawing 148 kb in Power Point slides by John Pugh (Homemade)
© Rickard Nebrér