Cdi Unit; Ignition Timing Control - Yamaha F4B Service Manual

CDI unit

When the permanent magnet a on the flywheel magnet a passes in front of the CDI unit b, the
exciter coil b in the CDI unit b induces an electric current c to produce a crank signal d that will
be transmitted to the ignition control circuit e. The electric current that has been induced by the
exciter coil b is also sent to charge the capacitor f.
When the ignition control circuit e transmits an ignition signal g, the capacitor f will discharge and
produce current h in the primary coil k, and induce a high voltage m in the secondary coil n to
ignite the spark plug c.
The CDI unit b ignites the spark plug c once per crankshaft rotation.
c
a
a

Ignition timing control

The CDI unit ignites the spark plug at the ignition timings that are programmed based on each
engine speed.
The engine speed will be calculated based on the crank signals that are input into the ignition con-
trol circuit.
b
d
e
f
k
h
g
Engine control system
b
c
n
m
2-2
0
1
2
3
4
5
6
7
8
9
10
A