Chapter 5. Electrical System - Yamaha GP 338F Servise Manual

ELECTRICAL SYSTEM
CHAPTER 5. ELECTRICAL SYSTEM
In the GPX338F/433F, the capacitor discharge ignition
system is used.
A capacitor discharge ignition (C.D.I.) system eliminates
the need for a mechanical contact breaker and its inher-
ent disadvantages. A simple electronic circuit using a
large storage capacitor and a thyristor (Silicon Controlled
Rectifier) provides a correctly-timed, high intensity vol-
tage to the spark plug .
The C.D.I. system has many advantages. There is no
contact breaker to wear out. become misaligned, or lose
its efficiency because of pitted points, increased gap, or
contamination. There is no mechanical adjustment re-
quired for the contact gap because there are no electrical
contacts (points) . Only a screwdriver and dial gauge are
required to set the timing. There is no mechanical spark
advance system to maintain, either.
An electronic circuit automatically provides the correct
spark advance at all engine speeds.
Finally, the C.D.I. system provides a stronger, quicker
primary current pulse.
This improves ignition performance, particularly at higher
r.p .m.'s. Additionally, the stronger pulse inhibits misfire
due to oil fouling and bridging.
The following diagrams show a comparison of ignition
performance between the contact breaker system and
the C.D.I. system.
2 "'"
1. Voltage
2. Milliseconds
3. Ignition voltage curve
Fig. 5-1
- 49 -
3
2
---~
___ _
1 Vo ltage
2. Mi lliseconds
3. Ignition voltage curve
Fig. 5·2
(1) C.D.I. systems and its function
The principal parts of the Yamaha C.D.I. System and
their primary function(s) are as follows:
1) Magneto - The Yamaha C.D.I. magneto is mounted
on the crankshaft and incorporates a charging coil
for the ignition capacitor and a pulser coil to gener-
ate a trigger pulse for ignition timing.
2) C.D.I. Unit - The "black box" of the system. This
solid state, encapsulated unjt contains the electronic
control circuitry, incl uding the ignition capacitor, sili-
con controlled rectifier (S.C.R.). charging current rec-
tifiers, and automatic spark advance circuit compo-
nents.
3) Ignition Coil - A "step- up" transformer which in-
creases the voltage from the ignition capacitor to the
high voltage is used to " fire" the spark plug.