Mariner Mercury 105/140 JET, Service Manual

Page: 70 / 797

90-824052R3 JUNE 2002 ELECTRICAL - 2A-19
IGNITION SWITCH (BULLET CONNECTIONS)
LOW SPEED/HIGH SPEED SPARK ADVANCE
MODULE DESCRIPTION:
MODEL SERIAL NUMBER
200 (Carbureted) 0D077248 thru
0D122746
The low speed/high speed spark advance
capabilities are combined in one module. If the
engine idle speed falls below approximately 550
RPM, the module will electronically advance the
timing by as much as 9
°
. This timing advance raises
the idle RPM to an acceptable level (550 RPM).
When the module senses the idle RPM is at the
acceptable level, it returns the timing to the normal
idle timing. The module also electronically
advances the timing by 6
°
when the engine speed
reaches 5000 RPM. The timing will remain
advanced until the engine speed exceeds 5600
RPM. Above 5600 RPM the high speed advance
module will retard the maximum timing by 4
°
to 6
°
.
Timing will remain retarded until engine speed is
reduced below 5600 RPM.
Low Speed/High Speed Spark Advance Module
TESTS FOR PROPER FUNCTION OF LOW
SPEED/ HIGH SPEED SPARK ADVANCE
MODULE
IMPORTANT: Due to the sensitivity characteris-
tics of individual modules and tachometer vari-
ances, the engine RPM at which the module will
advance/retard the ignition timing may vary
slightly from specification.
LOW SPEED SPARK ADVANCE TEST
Connect a timing light to No. 1 spark plug lead (top,
starboard bank). To test the low speed spark
advance function, start the engine and allow it to idle
above 600 RPM. Retard the ignition timing by slowly
pulling forward on the spark advance lever. The
system is functioning correctly if a rapid spark
advance (as much as 9
°
from the idle setting) is
observed as the engine speed slows down to below
approximately 550 RPM.
HIGH SPEED SPARK ADVANCE TEST
NOTE: If an engine dynamometer is available, the
high speed spark advance function can be checked
with a timing light while running the engine up to wide
open throttle. If a dynamometer is not available and
the boat/motor package will be lake tested, then it is
recommended that a DC voltmeter and a tachometer
be placed near one another inside the boat while the
engine is being run up to wide open throttle. The DC
voltmeter should be connected to read the NEGA-
TIVE voltage on the WHITE/BLACK wire relative to
engine ground. (The WHITE/BLACK wire connects
the output of the spark advance module to the two
switch boxes.) Normally, this voltage would be about
-30 to -35 volts DC at 5000 RPM, and should drop to
about half its previous value when the spark advance
function is activated above 5000 RPM.
NOTE: If engine speed exceeds 5600 RPM the NEG-
ATIVE voltage observed will begin to increase as the
maximum timing is retarded 4
°
to 6
°
.
NOTE: To read negative voltage, using some voltme-
ters, the red meter lead must be connected to engine
ground and the black meter lead connected to the
WHITE/BLACK wire.
The low speed/high speed spark advance module is
not repairable. Should the module fail to function as
described, it will require replacement.