Arctic Cat Panther 1974 Manual page 91

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THEORY OF OPERATION
breaker points are closed, the induceq voltage
flows through the points and to engine ground.
Since the magnets are alternately mounted, and
also, alternately pass the exciting coil, the magnetic
forces change direction of travel. Because the
magnetic forces travel from north to south
(positive to negative), the direction of flow changes
every 90 degrees of flywheel rotation. Therefore,
the electricity induced in the exciting coil winding
will also alternate in direction of flow. The term
for this type of flow is "alternating current".
Fig. IV-12
Magnet Breaker
Primary
1
Switches
After current is induced in the exciting coil, the
current flows to the external ignition coil
"primary", resulting in a magnetic induction with
the high voltage "secondary". To allow current
flow from the exciting coil to the low voltage
external ignition coil primary, the breaker points
and condenser must operate at a particular time
and sequence. As the crankshaft is rotating, the
breaker points open and close by means of an
activating cam that is attached to the breaker point
arm. When an engine is timed properly (16
0
BTDC), the breaker points are in an open position,
and this coincides with the maximum positive
amplitude of the voltage (current) flowing from
the exciting coil. The current flows to the external
ignition coil primary when the breaker points
open, Fig. IV-12, and in turn, breaks the exciting
coil circuit to ground, which is on the base plate.
As a result, the current flows through the external
ignition coil "primary", Fig. IV-12.
Like a transformer, the external ignition coil con -
sists of two separate windings; a low voltage
"primary" and high voltage "secondary", Fig.
IV-12. As current flows through the "primary",
the magnetic field builds up, resulting in induction
of the "secondary". Because of the required high
voltage current that is needed to jump the air gap
between the spark plugs center and side electrode,
a considerable increase in voltage must take place .
And how is this increase in voltage accomplished?
The wire turn ratio of the secondary is
considerably more than that of the primary, which
accounts for the increased secondary output.
Because the secondary has a high voltage output, it
is wound above the primary, which prevents a
short c ircu it of the coi I. Being that the secondary is
wound above the primary, the magnetic force lines
of the primary are broken, resulting in the
induction of an EMF (electromotive force) in the
secondary. Therefore, the secondary allows high
voltage current to flow to the spark plug and jump
the air gap between the center and side electrode,
Fig. IV-12. At the moment of spark, the
compressed fuel/air mixture in the combustion
chamber is ignited, causing expansion and a single
power impulse (see Section II, Engine Servicing,
Theory of Operation, pages 11-2 and 3).
The condenser is made of foil sheets with
high-quality insulation between them. It is
connected in parallel between the exciting coil and
breaker points, Fig. IV-12, and its function is to
absorb excess (unwanted) voltage when the points
open. This decreases the arc that would normally
occur between the points if there would not be a
condenser in the circuit. Without the condenser,
the breaker points would burn in a short time.
Other components that function in the ignition
system, but are not mounted on the engine, are:
the ignition switch, throttle safety switch, and the
emergency kill switch, Fig. IV-12. The switches are
all connected in parallel with the external ignition
coil primary and the engine frame, which also
serves as a common ground. If anyone of the
switches is closed (OFF), the induced exciting coil
current is routed to ground, rather than allowing
the current to flow to the external ignition coil and
spark plug. Therefore, a closed ignition switch,
emergency shut-off switch, or throttle safety
switch will not allow the engine to start due to the
absence of ignition spark.
Working between the throttle lever and
carburetor-mounted throttle, with the ability to
sense a frozen · or jammed throttle, is the
spring-actuated throttle safety switch. When
throttle cable is tensioned properly at the
carburetor-mounted throttle arm, the switch is
IV-7