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Ignition System (on Kz550-c); Pick-up Coil - Kawasaki KZ400 Service Manual

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The ignition system for this model
i 3
essentially a
battery and coil ignition sy5tem where the battery sup-
plies the current for the primary circuit in the ignition
system. However, this ignition system i s transistorized
and controls the current for the primary circuit by
use o f a solid state electronic switching unit called a
Darlington power transistor. The power transistors are
triggered by pick-up coils and there are no mechanical
breaker points, so the only periodic maintenance needed
i s automatic timing advancer lubrication (Pg. 262). Since
contact breaker heel wear (with resultant retarded igni-
tion timing) and breaker point pitting or burning are
eliminated, periodic inspection and adjustment of the
ignition timing are not required.
Ordinarily in a 4-stroke engine, a spark jumps acros
the spark plug electrodes only every other time that
the piston for that spark plug rises (once every 720'
of crankshaft rotation). This i s because between each
compression stroke, in which a fuellair mixture ready
for combustion is in the cylinder, there is an exhaust
stroke, in which the piston rises only to push out
t h e
burned gases. However, even i f a spark does jump across
the electrodes during the exhaust stroke, there i s no
effect since there is no compression and no fuel to burn.
Therefore, to eliminate any need for a distributor (thus
simplifying the system and making it more reliable), the
system is constructed so that both sparkoplugs fire every
time both pistons rise (once every 360 o f crankshaft
rotation) although one piston is on the compression
stroke and the other on the exhaust stroke.
Because the two spark plugs are connected in series,
the current through one spark plug also must go through
the other. Consequently, i f a spark will not jump across
the electrodes of one spark plug (due to dirty electrodes,
faulty plug lead, etc.), no spark will jump across the
electrodes o f the other plug as well.
The working electrical part of the ignition system
consists of a battery, two pick-up coils, an IC igniter,
two ignition coils, and four spark plugs. T o advance
the ignition timing as engine rpm rises, an automatic
centrifugal-type timing advancer i s used. The ignition
system comprises two parts, one part fires
cylinders, and the other part
cylinders. A
schematic wiring diagram o f one half the system is
shown in Fig.
The other half is identical. Both
work as follows.
Pick-up Coil
The pick-up coil assembly (a magnetic impulse gener-
ator) resembles the standard contact breaker assembly in
most respects except that the two
o f breaker points
have been eliminated.
In their places i s an iron timing
rotor and two magnetic pick-up coils.
Each pick-up
coil assembly consists of a pair o f permanent magnets
and a pick-up coil on a mounting plate. The timing
rotor which i s attached to the timing advancer has one
projection. As the projection on the timing rotor passes
through the magnetic field created by the permanent
magnets on the mounting plate, a magnetic field alter-
nately builds up and collapses. Each time the projection
passes a pick-up coil core an electric current i s devel-
oped. Each voltage pulse is conducted to the IC igniter
where i t is amplified and switches the Darlington power
transistor on and off to control the primary current.
Ignition Circuit
lgnition Engine Stop
Ignition Coil
Spark Plugs
P i c k - U ~


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