TOHATSU 40 Service Manual page 194

Pulser Coil Set
Each pulser coil in the coil consists of a permanent magnet with
many windings of wire wrapped around it. The flywheel has a
metallic cam, called an interrupter, molded on it. When the
interrupter passes in close proximity to the pulser coil, the lines of
force produced by the permanent magnet collapse momentarily. At
cranking speed this produces a 4.75 to 5.0 DVA signal in the coil.
The output voltage from each pulser coil is used to control a small
electronic switch (SCR) located inside of the CD Unit. When the CD
Unit receives an output from a pulser coil, it directs an output,
approximately 220 DVA, to the appropriate ignition coil primary.
• 3 cylinder models - Three pulser coils are provided, one per cylinder.
• 4 cylinder models - Four pulser coils are provided, one per
cylinder.
CDUnit
The CD Unit has three major functions:
• The CD Unit receives its operating voltage from the exciter coil(s)
and converts it into pulsating direct current for storage.
• The CD Unit stores this pulsating direct current in a capacitor.
• The CD Unit uses a series of electronic switches (SCRs),
activated by pulser coil output, to select the correct ignition coil
primary winding for firing. The CD Unit has one SCR for each
ignition coil it controls.
Depending upon the engine model, the CD Unit will limit the engine
speed to about half its maximum RPM when the overheat sensor,
water pressure sensor, or oil level sensor signals an abnormal
condition. A safety feature provided by the CD Unit on all engine
models, is over-speed limitation. The 115, 120 and 140 model
engines have a third type of speed limitation. The CD Unit will limit
the top engine speed to about 1500 RPM if the RED/YELLOW lead
from the CD Unit to the remote control box is not properly
connected. Refer to the RPM Limitation Test section for more detail
on RPM limitation functions.
The engines of the models 115, 120 and 140 are provided with a
starting-automatic-advance mechanism that is described below.
Angle of
Choke solenoid
advance
when inactive 6 degrees
when active 6 degrees
IgnitionCoil
Each ignition coil consists of two windings of wire wrapped around
a compacted ferrite material. The coil has a primary and secondary
terminal connection and a ground plate.
Through mutual induction, the ignition coil transforms the output
from the CD Unit to as much as 40,000 volts to fire the spark plug.
• 3 cylinder models - Three ignition coils are provided, one per
cylinder.
3-/ 4-Cylinder
Period of connection
1 to 4 seconds
When the choke solenoid is
active, and 30 seconds after it
stops its operation
ELECTRICAL SYSTEM
7-15