Yamaha F150B, Service Manual

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Electronic control system
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Ignition timing control system
F150B uses ignition timing control system to control the ignition timing and the duration of ignition
coil energization. High output power, improved fuel economy, and low exhaust emissions are
attained by properly controlling the ignition timing and the duration of ignition coil energization in
response to every engine operating conditions, based on the signals from each sensor and the map
data.
Basic ignition timing
computation Optimal ignition timing is selected from the map data in accordance with
the signals from each sensor.
Computation for com-
pensation Ignition timing is advanced or retarded in response to the engine operat-
ing conditions determined by the signals from each sensor.
Stable idle
speed
As the idle speed drops, ignition timing is advanced to
make it stable. Ignition timing is retarded as the idle speed
gets higher.
Start-up
operation Engine startability is improved by applying the advanced
ignition timing at the engine start-up. Subsequently, the
ignition timing is controlled to go back to the standard angle
gradually.
compensati
on for
acceleration Ignition timing is temporarily retarded at acceleration to
improve the throttle response.
Shift-cutout When the conditions are met for implementing the shift cut-
out control, the specified angle is added to the ignition tim-
ing at every updating cycle until it reaches the shift-cutout
compensation angle. Otherwise, the specified angle is sub-
tracted from the ignition timing at every updating cycle until
it reaches 0°CA.
Ignition timing
restriction Engine
temperature
restriction Optimal ignition timing is selected from the map data
depending on the cooling water temperature detected by
the engine temperature sensor.
Ignition
timing upper
and lower
limits
restriction Limit values for advancing and retarding the ignition timing
are computed by the map data in accordance with the
engine speed detected by the pulser coil.
Computing the
duration of
energization The duration of ignition coil energization is controlled based on the engine
speed and the supply voltage to the ignition coil.