Kohler K9J Service Manual page 72

MAGNETO IGNITION
COIL
~----HIGH
TENSION LEAD
CONDENSER
w---TO
~
~TO
BREAKER
POINTS
Figure 8-2. Typical Flywheel Magneto Ignition Coil And Stator.
The stator windings are connected to the magneto
ignition coil. Current flow in the ignition coil
reaches its highest peak at the instant the mag-
netic flux reverses direction. This is the point at
which the .system is timed to provide a spark at
the spark plug.
The ignition coil has a low tension primary winding
and a high tension secondary winding. The secon-
dary winding has approximately 1 00 turns of wire
for every 1 turn in the primary. This relationship
causes the voltage induced in the secondary wind-
ing to be about 100 times higher than in the pri-
mary. If the magneto produces 250 volts in the
primary winding, the secondary winding voltage will
be 25,000 volts.
When ignition is required, the breaker points open
to break the primary circuit. The resultant sudden
collapse of the field around the primary winding
causes sufficient energy to be produced in the
secondary winding to bridge the spark plug gap.
The collapsing field also induces energy in the pri-
mary winding, but the condenser shunts this en-
ergy to ground, preventing it from bridging the
breaker point gap. Figure 8-2 shows a typical sta-
tor and coil assembly.
Magneto Ignition Timing
Engines are equipped with a timing sight hole
either in the bearing plate or in the blower hous-
ing. If a snap button covers the hole, pry it out
with a screwdriver or similar tool so that the timing
marks may be seen. Two marks will be present on
the flywheel; T for top dead center, and S or SP
for the firing point (20 deg. before top dead cen-
ter).
There are two ways to time a magneto ignition
system, static and timing light. The timing light
8.2
method is the more accurate of the two. A stor-
age battery is needed for use with most timing
lights.
Static Timing Method - Perform static timing as
follows.
1 . Remove the breaker point cover.
2. Remove the spark plug lead to prevent unin-
tentional starting of the engine.
3. Rotate the engine slowly by hand in the direc-
tion of normal operation. Rotation should be
clockwise when viewed from the flywheel end.
4. The breaker points should just begin to open
when the S ,or SP mark (T mark on Model
K91) appears in the center of the timing sight
hole. Continue rotating the engine until the
breaker points are fully opened.
5. Measure the breaker point gap with a feeler
gauge. The gap should be .020".
6. If the gap is not .020", loosen the gap adjust-
ment screw and adjust the gap.
7. Tighten the gap adjustment screw.
8. Replace the breaker point cover.
Timing Light Timing Method - Several different
types of timing lights are available. Follow the
manufacturer's directions for use. Perform timing
with a timing light as follows.
1 . Remove the lead from the spark plug.
2. Wrap one end of a short piece of fine bare
wire around the spark plug terminal and re-
place the lead. The free end of the wire must
protrude from beneath the rubber boot on the
lead.