Ignition System; Ignition Timing Control - Yamaha F100C Service Manual

Ignition system

The computer controlled CDI system has three basic modes of operation: starting, warm-up, and
normal operation.

Ignition timing control

Starting mode
Ignition timing is fixed at 10° BTDC. The starting mode cuts off when the engine has been started
and the engine speed is over 600 r/min.
Warm-up mode
The engine speed is kept at approximately 1,100 r/min by the computer. The four main situations,
based on the cooling water temperature, that this mode operates in are as follows:
1. Below 0 °C (32 °F), this mode lasts approximately 300 seconds.
2. From 0 °C (32 °F)–20 °C (68 °F), this mode lasts approximately 180 seconds.
3. From 20 °C (68 °F)–40 °C (104 °F), this mode lasts approximately 120 seconds.
4. Over 40 °C (104 °F), this mode does not operate.
The warm-up mode will cut off if the engine speed exceeds 4,000 r/min.
Normal operation
This mode operates between 5° ATDC and 35° BTDC. The ignition timing is automatically adjusted
by the computer. The computer receives three signals (i.e, crankshaft position, engine revolution,
and throttle position) every five microseconds, and then adjusts the ignition timing accordingly.
Two pulser coils send signals to the computer which then determines the crankshaft position and
engine revolution.
The throttle position sensor also sends signals to the computer which then determines the throttle
position. The microcomputer uses these three signals to determine the proper ignition timing.
Fail-safe controls
When the engine start switch is turned on, both low oil pressure and overheat warning lights will turn
on. After the engine is started and the engine operates normally, the warning lights will turn off.
This ignition system incorporates three Fail-safe controls that are described below.
• Over-revolution control
Over 6,150 r/min, the ignition to either cylinder #1 or #4 is cut. At 6,175 r/min, the ignition to
both cylinders #1 and #4 is cut. Over 6,200 r/min, the ignition to both cylinders #1 and #4, and
either #2 or #3 is cut. Over 6,225 r/min, the ignition to cylinders #1, #2, #3, and #4 is cut.
• Overheating control
From 0–2,000 r/min (after starting the engine), this mode will not operate for 60 seconds.
From 2,000 r/min, it will not operate for 21 seconds.
When the cooling water temperature is 95 °C (203 °F) or above, this mode starts. The buzzer
will sound and the warning light will turn on. Ignition to cylinders #1 and #4 will cut off and the
engine speed will gradually lower to approximately 2,000 r/min.
This mode will stop when the cooling water temperature is 79 °C (174 °F) and the throttle is
fully closed. The buzzer will then stop and the warning light will turn off.
60C5D11
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