Yamaha 55DEHD Service Manual page 253

Symptom 1: Poor performance
Symptom 2
Spark plug malfunction
Short or open connec-
tion in ignition coil cir-
cuit and ground circuit
Spark plug
sparks
Ignition coil malfunction
improperly
CDI unit malfunction
Does not advance
Ignition timing
improperly
Cylinder head gasket
malfunction
Low compres- Reed valves
sion pressure malfunction
Scratched piston or
wear the piston rings
Scratched cylinder
Propeller selection
—
improperly
Outboard motor mount-
—
ing height improperly
Gear damaged (pinion,
—
forward, reverse)
WD: See the wiring diagram
6885J11
Cause 1 Cause 2
Spark plug gap
improperly
Ignition coil
resistance out
of specifications
CDI unit output
peak voltage
less than speci-
fications
Ignition control
link broken
Control lever
stop screw
— loosened or
setting length
improperly
Trouble shooting the power unit
Checking step
Check the spark plug
gap and condition.
Check the wiring har-
—
ness continuity.
Change the ignition coil
and check the ignition
spark.
Measure the charge
coil output peak voltage
and resistance.
Check and adjust the
link rod.
Check the stop screw
locknut tightenings and
setting length.
Check the compression
pressure and disas-
—
sembling the cylinder
head.
Disassemble and
—
check the reed valves.
Check the compression
pressure and disas-
—
sembling the power
unit.
Check the propeller
—
matching.
Check the outboard
—
motor mounting height.
Disassemble the lower
case and check the
—
pinion, forward, reverse
gear.
Refer
to
1
page
3-3
2
WD
5-6
8-4
3
8-7
4
—
3-8
5
5-1
6
5-18
5-14
7
5-1
5-9
1-13
8
1-14
6-10
9
6-16
6-16
9-6