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Ducati 750 Sport Owner's Manual Page 64

Ducati motorcycles owner's manual.
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Ignition is by capacitor discharge. The current from the generator is fed through a capacitor
which discharges through a static element controlled by the generator on the transducer's
primary circuit.
The secondary circuit produces a high tension voltage which is fed to the spark plugs.
The transducer connected to the red cable (vertical head) produces a fully advanced spark as
the rotor hole and corresponding stator plate hole coincide.
After a 2700 clockwise rotation (looking at the generator) high tension current is produced in
the transducer serving the horizontal cylinder. At engine speeds lower than 1,700 r.p.m.
:! 300, the high tension impulse produced by both transducers is retarded by 280. The total
advance available in the range 1,400 to 2,000 r.p.m. being 280 :! 20.
To stop the engine it is necessary to ground the two transducers, either at the emergency
switch on the right handle bar or by using the ignition key. The two transducer leads are linked
to the one emergency switch lead through a device located inside the headlamp assembly,
and consisting of a diode and two resistors. The stator plate is a single unit which includes two
feeding coils, one for each cylinder, providing the current to charge the two capacitors, and
two magnetic pick ups one for each cylinder, controlling the timing of the capacitor discharge.
Each of these pick ups consists of two coils, positioned at a phase angle appropriate to the
ignition timing for each cylinder. '
The rotor is also a single unit fitting on to the crankshaft inside the permanent inductor
The high tension transducer includes the high tension coil and electronic components. The
three connectors run to the generator and to earth, the earth wire being brown, the high
tension outlet has a screw clip which connects on to the spark plug cable.
To check the system without using instru ments simply ensure that the wiring and connections
are in good order and replace any obviously worn or faulty parts. Thorough testing, however,
does require the use of the following:
a) Meter: to check the resistance.
b) Stroboscope: pistol type for attachment to the spark plug leads.
c) Test bench: to check the system dismounted from the motor cycle, and providing the
following facilties:
-Speed range: 0 to 8,000 r.p.m.
-Speed indicator: to show r.p.m.
- Three point spark gap: to check ignition phasing. .
-High tension peak voltmeter: to measure the H.T. voltâge unloaded (range 1-4,000V).
- Oscilloscope with H.T. cord (50KV): to check low tension and high tension values and wave
shape regularity-green, red and white cables.
DEFECT: Engine wil not start (plugs not sparking).
a) Check transducer and generator connections.
b) Check the operation of the two ignition switches (key and emergency); they may be faulty
or damp, earthing the diodes of the linking device in the headlight assembly.
c) Check whether the diodes mentioned above are shorted out using an Ohmmeter as shown
in Figure 2.


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