Yamaha F2.5C User manual

F25C
SERVICE MANUAL
6D5-28197-5F-11
290539

NOTICE
This manual has been prepared by Yamaha primarily for use by Yamaha dealers and their trained
mechanics when performing maintenance procedures and repairs to Yamaha equipment. It has
been written to suit the needs of persons who have a basic understanding of the mechanical and
electrical concepts and procedures inherent in the work, for without such knowledge attempted
repairs or service to the equipment could render it unsafe or unfit for use.
Because Yamaha has a policy of continuously improving its products, models may differ in detail
from the descriptions and illustrations given in this publication. Use only the latest edition of this
manual. Authorized Yamaha dealers are notified periodically of modifications and significant
changes in specifications and procedures, and these are incorporated in successive editions of this
manual.
Important information 1
Particularly important information is distinguished in this manual by the following notations:
The Safety Alert Symbol means ATTENTION! BECOME ALERT! YOUR SAFETY IS
INVOLVED!
WARNING
Failure to follow WARNING instructions could result in severe injury or death to the machine
operator, a bystander, or a person inspecting or repairing the outboard motor.
CAUTION:
A CAUTION indicates special precautions that must be taken to avoid damage to the out-
board motor.
NOTE:
A NOTE provides key information to make procedures easier or clearer.
F25C
SERVICE MANUAL
©2003 by Yamaha Motor Co., Ltd.
1st Edition, November 2003
All rights reserved.
Any reprinting or unauthorized use
without the written permission of
Yamaha Motor Co., Ltd.
is expressly prohibited.
Printed in Japan

Contents
General information 1
GEN
INFO
Specifications 2
SPEC
Periodic checks and adjustments 3
CHK
ADJ
Fuel system 4
FUEL
Power unit 5
POWR
Lower unit 6
LOWR
Bracket unit 7
BRKT
Electrical systems 8
ELEC
Troubleshooting 9
TRBL
SHTG
Index
–+

6D55F11
GEN
INFO
1
2
3
4
5
6
7
8
9
General information
How to use this manual.................................................................................1-1
Manual format............................................................................................1-1
Symbols.....................................................................................................1-2
Safety while working......................................................................................1-3
Fire prevention...........................................................................................1-3
Ventilation..................................................................................................1-3
Self-protection ...........................................................................................1-3
Parts, lubricants, and sealants ..................................................................1-3
Good working practices .............................................................................1-4
Disassembly and assembly .......................................................................1-4
Identification...................................................................................................1-5
Applicable models .....................................................................................1-5
Serial number ............................................................................................1-5
Propeller selection.........................................................................................1-5
Propeller size.............................................................................................1-5
Selection....................................................................................................1-6
Predelivery checks ........................................................................................1-6
Checking the fuel system ..........................................................................1-6
Checking the engine oil level.....................................................................1-6
Checking the gear oil level ........................................................................1-6
Checking the outboard motor mounting height..........................................1-7
Checking the remote control cables (remote control model) .....................1-7
Checking the steering system ...................................................................1-8
Checking the gear shift and throttle operation...........................................1-8
Checking the engine stop lanyard switch ..................................................1-9
Checking the cooling water pilot holes ......................................................1-9
Test run .....................................................................................................1-9
Break-in ...................................................................................................1-10
After test run ............................................................................................1-10

GEN
INFO General information
1-1 6D55F11
How to use this manual 1
Manual format
The format of this manual has been designed to make service procedures clear and easy to under-
stand. Use the information below as a guide for effective and quality service.
1Parts are shown and detailed in an exploded diagram and are listed in the components list.
2Tightening torque specifications are provided in the exploded diagrams and after a numbered
step with tightening instructions.
3Symbols are used to indicate important aspects of a procedure, such as the grade of lubricant
and lubrication point.
4The components list consists of part names and part quantities, as well as bolt and screw dimen-
sions.
5Service points regarding removal, checking, and installation are shown in individual illustrations
to explain the relevant procedure.
NOTE:
For troubleshooting procedures, see Chapter 9, “Troubleshooting.”
LOWR Lower unit
6-5 62Y5A11
Lower unit
No. Part name Q’ty Remarks
1 Lower unit 1
2 Plastic tie 1 Not reusable
3Hose 1
4 Check screw 1
5 Gasket 2 Not reusable
6 Dowel pin 2
7 Bolt 4 M10 40 mm
8 Drain screw 1
9Grommet 1
10 Bolt 1 M10 45 mm
11 Bolt 1 M8 60 mm
12 Thrust washer 1
13 Propeller 1
14 Washer 1
15 Washer 1
16 Cotter pin 1 Not reusable
17 Propeller nut 1
18 Trim tab 1
LOWR Lower unit
6-19 62Y5A11
Removing the drive shaft
1. Remove the drive shaft assembly and
pinion, and then pull out the forward
gear.
Disassembling the drive shaft
1. Install the pinion nut 1, tighten it finger
tight, and then remove the drive shaft
bearing 2using a press.
CAUTION:
•Do not press the drive shaft threads a
directly.
•Do not reuse the bearing, always
replace it with a new one.
Disassembling the forward gear
1. Remove the taper roller bearing from the
forward gear using a press.
CAUTION:
Do not reuse the bearing, always replace
it with a new one.
2. Remove the needle bearing from the for-
ward gear.
CAUTION:
Do not reuse the bearing, always replace
it with a new one.
Drive shaft holder 4 1: 90890-06518
Pinion nut holder 2: 90890-06505
Socket adapter 2 3: 90890-06507
Bearing inner race attachment 3:
90890-06639
S62Y6850K
Bearing separator 1: 90890-06534
Stopper guide plate 2: 90890-06501
Stopper guide stand 3:
90890-06538
Bearing puller 4: 90890-06535
Bearing puller claw 1 5:
90890-06536
S62Y6740K
5
4
321

6D55F11 1-2
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7
8
9
Symbols
The symbols below are designed to indicate the content of a chapter.
General information
Specifications
Periodic checks and adjustments
Fuel system
Power unit
Lower unit
Bracket unit
Electrical systems
Troubleshooting
GEN
INFO
SPEC
CHK
ADJ
FUEL
POWR
LOWR
BRKT
ELEC
TRBL
SHTG
–+
Symbols 1to 6indicate specific data.
1Special tool
2Specified oil or fluid
3Specified engine speed
4Specified tightening torque
5Specified measurement
6Specified electrical value
(resistance, voltage, electric current)
Symbols 7to Cin an exploded diagram indicate the grade of lubricant and the lubrication point.
7Apply Yamaha 4-stroke motor oil
8Apply gear oil
9Apply water resistant grease (Yamaha grease A)
0Apply molybdenum disulfide grease
AApply corrosion resistant grease
(Yamaha grease D)
BApply low temperature resistant grease
(Yamaha grease C)
CApply injector grease
Symbols Dto Iin an exploded diagram indicate the type of sealant or locking agent and the appli-
cation point.
DApply Gasket Maker
EApply Yamabond No. 4
FApply LOCTITE 271 (red)
GApply LOCTITE 242 (blue)
HApply LOCTITE 572
IApply silicon sealant
123456
T
R
.
.
7890ABC
E G
A M
D
C I
DEFGHI
GM
4
271
LT
242
LT
572
LT SS
How to use this manual

GEN
INFO General information
1-3 6D55F11
Safety while working 1
To prevent an accident or injury and to
ensure quality service, follow the safety pro-
cedures provided below.
Fire prevention
Gasoline is highly flammable.
Keep gasoline and all flammable products
away from heat, sparks, and open flames.
Ventilation
Gasoline vapor and exhaust gas are heavier
than air and extremely poisonous. If inhaled
in large quantities they may cause loss of
consciousness and death within a short time.
When test running an engine indoors (e.g., in
a water tank) be sure to do so where ade-
quate ventilation can be maintained.
Self-protection
Protect your eyes by wearing safety glasses
or safety goggles during all operations involv-
ing drilling and grinding, or when using an air
compressor.
Protect your hands and feet by wearing pro-
tective gloves and safety shoes when neces-
sary.
Parts, lubricants, and sealants
Use only genuine Yamaha parts, lubricants,
and sealants or those recommended by
Yamaha, when servicing or repairing the out-
board motor.
Under normal conditions, the lubricants men-
tioned in this manual should not harm or be
hazardous to your skin. However, you should
follow these precautions to minimize any risk
when working with lubricants.
1. Maintain good standards of personal and
industrial hygiene.
2. Change and wash clothing as soon as
possible if soiled with lubricants.
3. Avoid contact with skin. Do not, for
example, place a soiled rag in your
pocket.
4. Wash hands and any other part of the
body thoroughly with soap and hot water
after contact with a lubricant or lubricant
soiled clothing has been made.
5. To protect your skin, apply a protective
cream to your hands before working on
the outboard motor.

6D55F11 1-4
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7
8
9
6. Keep a supply of clean, lint-free cloths for
wiping up spills, etc.
Good working practices
Special service tools
Use the recommended special service tools
to protect parts from damage. Use the right
tool in the right manner—do not improvise.
Tightening torques
Follow the tightening torque specifications
provided throughout the manual. When tight-
ening nuts, bolts, and screws, tighten the
large sizes first, and tighten fasteners starting
in the center and moving outward.
Non-reusable parts
Always use new gaskets, seals, O-rings, cot-
ter pins, circlips, etc., when installing or
assembling parts.
Disassembly and assembly
1. Use compressed air to remove dust and
dirt during disassembly.
2. Apply engine oil to the contact surfaces
of moving parts before assembly.
3. Install bearings with the manufacture
identification mark in the direction indi-
cated in the installation procedure. In
addition, be sure to lubricate the bearings
liberally.
4. Apply a thin coat of water-resistant
grease to the lip and periphery of an oil
seal before installation.
5. Check that moving parts operate nor-
mally after assembly.
Safety while working

GEN
INFO General information
1-5 6D55F11
Identification 1
Applicable models
This manual covers the following models.
Serial number
The outboard motor serial number is
stamped on a label attached to the port
clamp bracket.
1Model name
2Approved model code
3Transom height
4Serial number
Propeller selection 1
The performance of a boat and outboard
motor will be critically affected by the size
and type of propeller you choose. Propellers
greatly affect boat speed, acceleration,
engine life, fuel economy, and even boating
and steering capabilities. An incorrect choice
could adversely affect performance and
could also seriously damage the engine.
Use the following information as a guide for
selecting a propeller that meets the operating
conditions of the boat and the outboard
motor.
Propeller size
The size of the propeller is indicated on a
propeller blade, on the propeller boss end, on
the side of the propeller boss.
Applicable models
F25CMH, F25CM
Model name Approved
model code
Starting
serial No.
F25CMH 6D5
S: 1000001–
L: 1000001–
F25CM L: 1000001–
S69W1030
× -
abc
S69W1040
× -
abc
S69W1050
× -
abc

6D55F11 1-6
1
2
3
4
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6
7
8
9
aPropeller diameter (in inches)
bPropeller pitch (in inches)
cPropeller type (propeller mark)
Selection
When the engine speed is at the full throttle
operating range (5,000–6,000 r/min), the
ideal propeller for the boat is one that pro-
vides maximum performance in relation to
boat speed and fuel consumption.
Predelivery checks 1
To make the delivery process smooth and
efficient, the predelivery checks should be
completed as explained below.
Checking the fuel system
1. Check that the fuel hoses are securely
connected and that the fuel tank is full
with fuel.
CAUTION:
This is a 4-stroke engine. Never use pre-
mixed fuel.
Checking the engine oil level
1. Check the engine oil level.
NOTE:
If the engine oil is below the minimum level
mark b, add sufficient oil until the level is
between aand b.
Checking the gear oil level
1. Check the gear oil level.
Propeller size (in) Material
9 7/8 ×8 - F
Aluminum
9 7/8 ×9 - F
9 7/8 ×10 1/2 - F
9 7/8 ×11 1/4 - F
9 7/8 ×12 - F
9 7/8 ×13 - F
9 7/8 ×14 - F
Recommended engine oil:
4-stroke motor oil
API: SE, SF, SG, SH, or SJ
SAE: 10W-30 or 10W-40
Oil quantity:
With oil filter replacement:
1.9 L (2.0 US qt, 1.7 Imp qt)
S60V1290
Identification / Propeller selection / Predelivery checks

GEN
INFO General information
1-7 6D55F11
Checking the outboard motor
mounting height
1. Check that the anti-cavitation plate is
between the bottom of the boat and a
maximum of 25 mm (1 in) abelow it. If
the mounting height is too high, cavita-
tion will occur and propulsion will be
reduced. Also, the engine speed will
increase abnormally and cause the
engine to overheat. If the mounting
height is too low, water resistance will
increase and reduce engine efficiency.
NOTE:
The optimum mounting height is affected by
the combination of the boat and the outboard
motor. To determine the optimum mounting
height, test run the outboard motor at differ-
ent heights.
2. Check that the clamp brackets are
secured with the clamp screws.
Checking the remote control cables
(remote control model)
1. Set the remote control lever to the neu-
tral position and fully close the throttle
lever.
2. Check that the throttle cam 1contacts
the fully closed stopper 2.
3. Check that the shift link lever 3is verti-
cal to the mating surfaces of the engine.
WARNING
The shift/throttle cable joint must be
screwed in a minimum of 8.0 mm (0.31 in)
a.
S6D51030
a
S6D51040
21
S6D53190
a

6D55F11 1-8
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9
Checking the steering system
1. Check the steering friction for proper
adjustment.
NOTE:
•To increase the friction, turn the friction
adjusting bolt in direction a.
•To decrease the friction, turn the friction
adjusting bolt in direction b.
2. Check that the steering operates
smoothly.
3. Check that there is no interference with
wires or hoses when the outboard motor
is steered.
Checking the gear shift and throttle
operation
1. Check that the gear shift operates
smoothly when the remote control lever
or shift lever is shifted from neutral to for-
ward or reverse.
2. Check that the throttle operates smoothly
when the throttle grip (tiller handle
model) is turned from the fully closed
position to the fully open position a.
Check that the throttle operates smoothly
when the remote control lever (remote
control model) is shifted from forward or
reverse to the fully open positions a.
S6D51070
S6D51080
S6D51090
R
F
N
a
START
FAST
0 100%
S6D51130
F
N
R
a
a
Predelivery checks

GEN
INFO General information
1-9 6D55F11
Checking the engine stop lanyard
switch
1. Check that the engine turns off when the
engine stop lanyard switch is pushed or
the engine stop lanyard is pulled from the
engine stop lanyard switch.
ÈTo outboard motor
Checking the cooling water pilot
holes
1. Check that cooling water is discharged
from the cooling water pilot holes.
Test run
1. Start the engine, and then check that the
gear shift operates smoothly.
2. Check the engine idle speed after the
engine has been warmed up.
3. Operate at trolling speed.
4. Run the outboard motor for 1 hour at
2,000 r/min or at half throttle, then for
another hour at 3,000 r/min or at 3/4
throttle.
5. Check that the outboard motor does not
tilt up when shifting into reverse and that
water does not flow in over the transom.
NOTE:
The test run is part of the break-in operation.
S6D51100
S6D51110
S6D53140

6D55F11 1-10
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Break-in
During the test run, perform the break-in
operation in the following three stages.
1. One hour aat 2,000 r/min or at approxi-
mately half throttle
2. One hour bat 3,000 r/min or 3/4 throttle
and 1 minute out of every 10 at full throt-
tle
3. Eight hours cat any speed, however,
avoid running at full speed for more than
5 minutes
ÈHour
After test run
1. Check for water in the gear oil.
2. Check for fuel leakage in the cowling.
3. Flush the cooling water passage with
fresh water using the flushing kit and with
the engine running at idle.
S69J1240
01210
È
ab c
Predelivery checks

GEN
INFO General information
1-11 6D55F11
— MEMO —

6D55F11
SPEC
1
2
3
4
5
6
7
8
9
Specifications
General specifications...................................................................................2-1
Maintenance specification ............................................................................2-3
Power unit..................................................................................................2-3
Lower unit ..................................................................................................2-7
Electrical ....................................................................................................2-7
Dimensions................................................................................................2-9
Tightening torques.......................................................................................2-11
Specified torques.....................................................................................2-11
General torques.......................................................................................2-13

SPEC Specifications
2-1 6D55F11
General specifications 2
Item Unit Model
F25CMH F25CM
Dimension
Overall length mm (in) 1,151 (45.3) 703 (27.7)
Overall width mm (in) 430 (16.9) 376 (14.8)
Overall height
(S) mm (in) 1,148 (45.2) —
(L) mm (in) 1,275 (50.2)
Boat transom height
(S) mm (in) 381 (15.0) —
(L) mm (in) 508 (20.0)
Weight
(with aluminium propeller)
(S) kg (lb) 62.0 (137) —
(L) kg (lb) 64.0 (141) 63.0 (139)
Performance
Maximum output kW (hp) 18.4 (25.0) at 5,500 r/min
Full throttle operating range r/min 5,000–6,000
Maximum fuel consumption L (US gal,
lmp gal)/hr
9.2 (2.4, 2.0) at 6,000 r/min
Engine idle speed r/min 925–1,025
Power unit
Type In-line, 4-stroke, SOHC, 4 valves
Cylinder quantity L2
Total displacement cm3(cu. in) 498 (30.4)
Bore ×stroke mm (in) 65.0 ×75.0 (2.56 ×2.95)
Compression ratio 9.87
Control system Tiller handle Remote control
Starting system Manual
Enrichment system Prime Start
Ignition system Microcomputer (CDI)
Maximum generator output V, W 12, 80
Spark plug DPR6EA-9 (NGK)
Cooling system Water
Exhaust system Propeller boss
Lubrication system Wet sump

6D55F11 2-2
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(*1) RON: Research Octane Number
(*2) Meeting both API and SAE requirements
Fuel and oil
Fuel type Regular unleaded gasoline
Fuel minimum rating RON(*1) 86
Engine oil 4-stroke motor oil
Engine oil grade
API
SAE
SE, SF, SG, SH, or SJ
10W-30 or 10W-40
Engine oil quantity
(without oil filter replacement) L (US qt,
lmp qt)
1.7 (1.8, 1.5)
(with oil filter replacement) L (US qt,
lmp qt)
1.9 (2.0, 1.7)
Gear oil type Hypoid gear oil
Gear oil grade(*2) API
SAE
GL-4
90
Gear oil quantity cm3
(US oz,
lmp oz)
320 (10.8, 11.3)
Bracket unit
Tilt angle
(at 12°boat transom)
Degree 8, 12, 16, 20, 24
Tilt-up angle Degree 64
Shallow water drive angle Degree 29, 43
Steering angle Degree 45 + 45
Drive unit
Gear shift positions F-N-R
Gear ratio 2.08 (27/13)
Reduction gear type Spiral bevel gear
Clutch type Dog clutch
Propeller shaft type Spline
Propeller direction (rear view) Clockwise
Propeller identification mark F
Item Unit Model
F25CMH F25CM
General specifications

SPEC Specifications
2-3 6D55F11
Maintenance specification 2
Power unit
Item Unit Model
F25CMH F25CM
Power unit
Minimum compression
pressure(*1)
kPa
(kgf/cm2, psi)
810 (8.1, 115)
Lubrication oil pressure(*2) kPa
(kgf/cm2, psi)
80 (0.8, 11) at engine idle speed
Cylinder heads
Warpage limit mm (in) 0.10 (0.0039)
(lines indicate straightedge
position)
Cylinder head journal inside
diameter
mm (in) 37.000–37.025 (1.4567–1.4577)
Cylinders
Bore size mm (in) 65.000–65.015 (2.5590–2.5596)
Taper limit mm (in) 0.08 (0.0032)
Out-of-round limit mm (in) 0.05 (0.0020)
Pistons
Piston diameter (D) mm (in) 64.950–64.965 (2.5571–2.5577)
Measuring point (H) mm (in) 2.0 (0.08)
Piston-to-cylinder clearance mm (in) 0.035–0.065 (0.0014–0.0026)
Piston pin boss bore mm (in) 15.974–15.985 (0.6289–0.6293)
Oversize piston diameter
1st mm (in) 65.200–65.215 (2.5669–2.5675)
2nd mm (in) 65.450–65.465 (2.5768–2.5774)
Piston pins
Outside diameter mm (in) 15.965–15.970 (0.6285–0.6287)
(*1) Measure conditions:
•Ambient temperature 20 °C (68 °F), wide open throttle, with spark plugs removed from all cylinders.
The figures are for reference only.
•Since this outboard motor is equipped with an automatic decompression mechanism, accurate data may
be difficult to obtain due to differences in the way the starer rope is pulled.
(*2) The figures are for reference only.