Yamaha 2009 YW125Y User manual

2009
MOTORCYCLE
SERVICE MANUAL
Model : YW125Y_
32SF819770E0 *32SF819770E0*

EAS00000
YW125Y 2009
SERVICE MANUAL
©2008 byYamaha MotorTaiwan Co., Ltd.
First edition, July 2008
All rights reserved.
Any reproduction or unauthorized use
without the written permission of
Yamaha Motor Taiwan Co., Ltd.
is expressly prohibited.
0.10 ~ 0.14mm
(0.004 ~ 0.006in)
0.16 ~ 0.20mm
(0.006 ~ 0.008in)
Valve Clearance (cold)
Intake
Exhuast
Spark plug gap
0.7 ~ 0.8 mm (0.028 ~ 0.031in)
Spark Plug
U22ESR-N (DENSO)
CR7E (NGK)

EAS20070
IMPORTANT
This manual was produced by theYamaha MotorTaiwan Company, Ltd.primarily for use byYamaha
dealers and their qualified mechanics. It is not possible to include all the knowledge of a mechanic in
one manual.Therefore, anyone who uses this book to perform maintenance and repairs onYamaha
vehicles should have a basic understanding of mechanics and the techniques to repair these types
of vehicles. Repair and maintenance work attempted by anyone without this knowledge is likely to
render the vehicle unsafe and unfit for use.
This model has been designed and manufactured to perform within certain specifications in regard
to performance and emissions. Proper service with the correct tools is necessary to ensure that the
vehicle will operate as designed. If there is any question about a service procedure, it is imperative
that you contact aYamaha dealer for any service information changes that apply to this model.This
policy is intended to provide the customer with the most satisfaction from his vehicle and to conform
to federal environmental quality objectives.
Yamaha MotorTaiwan Company, Ltd.is continually striving to improve all of its models.Modifications
and significant changes in specifications or procedures will be forwarded to all authorized Yamaha
dealers and will appear in future editions of this manual where applicable.
TIP
• This Service Manual contains information regarding periodic maintenance to the emission con-
trol system. Please read this material carefully.
• Designs and specifications are subject to change without notice.
EAS20080
IMPORTANT MANUAL INFORMATION
Particularly important information is distinguished in this manual by the following notations.
This is the safety alert symbol. It is used to alert you to potential personal
injury hazards. Obey all safety messages that follow this symbol to avoid
possible injury or death.
AWARNING indicates a hazardous situation which,if not avoided,could
result in death or serious injury.
A NOTICE indicates special precautions that must be taken to avoid
damage to the vehicle or other property.
A TIP provides key information to make procedures easier or clearer.
Q
TIP
WARNING
NOTICE

EAS00007 HOWTO USETHIS MANUAL
This manual is intended as a handy, easy-to-read reference book for the mechanic.Comprehensive
explanations of all installation, removal, disassembly, assembly, repair and check procedures are
laid out with the individual steps in sequential order.
1The manual is divided into chapters. An abbreviation and symbol in the upper right corner of
each page indicate the current chapter.]
Refer to “SYMBOLS”.
2Each chapter is divided into sections.The current section title is shown at the top of each page,
except in Chapter 3 (“PERIODIC CHECKS AND ADJUSTMENTS”), where the sub-section
title(s) appears.
3Sub-section titles appear in smaller print than the section title.
4To help identify parts and clarify procedure steps, there are exploded diagrams at the start of
each removal and disassembly section.
5Numbers are given in the order of the jobs in the exploded diagram. A circled number indicates
a disassembly step.
6Symbols indicate parts to be lubricated or replaced.
Refer to “SYMBOLS”.
7Ajob instruction chart accompaniesthe exploded diagram,providingtheorder of jobs,namesof
parts, notes in jobs, etc.
8Jobs requiring more information (such as special tools and technical data) are described se-
quentially.
5-32
ENG
RemarksOrder Job/Part Q’ty
1
2
3
4
5
6
7
8
EAS00251
CYLINDER AND PISTON
Removing the cylinder and piston
Cylinder head
Timing chain guide (exhaust side)
Cylinder
Dowel pin
Cylinder gasket
Piston pin clip
Piston pin
Piston
Piston ring set
Remove the parts in the order listed.
Refer to “CYLINDER HEAD”.
Refer to “REMOVING THE CYLINDER
AND PISTON” and “INSTALLING THE
PISTON AND CYLINDER”.
Forinstallation, reversethe removalpro-
cedure.
1
1
2
1
2
1
1
1
CYLINDER AND PISTON
5
8
65
3
3
4
2
1
7
ENG
5-33
3
2
1
EAS00253
REMOVINGTHE CYLINDER AND PISTON
1. Remove:
8piston pin clip 1
8piston pin 2
8piston 3
NOTICE
Do not use a hammer to drive the piston pin
out.
TIP
8Before removing the piston pin clip, cover
the crankcase opening with a clean rag to
prevent the piston pin clip from falling into
the crankcase.
8Before removing the piston pin, deburr the
piston pin clip’s groove and the piston’s pin
borearea.
8If both areas are deburred and the piston
pin is still difficult to remove, remove it with
the piston pin puller set 4.
Piston pin puller set
90890-01304 (YU-01304)
CYLINDER AND PISTON
2. Remove:
8top ring
82nd ring
8oil ring
TIP
When removing a piston ring, open the end gap
with your fingers and lift the other side of the
ring over the piston crown.
32
4
4
5
7
6 2 1
3
8

GEN
INFO
SPEC
CHK
ADJ
ENG
TRBL
SHTG
CHAS
-+
ELEC
4M
B
LS
New
M
G
COOL
12
34
56
78
90
qw
er
i
s
hj
EAS00008
SYMBOLS
The following symbols are not relevant to every
vehicle.
Symbols 1to 9indicate the subject of each
chapter.
1Generalinformation
2Specifications
3Periodic checks and adjustments
4Chassis
5Engine
6Cooling system
7Fuel injection system
8Electrical system
9Troubleshooting
Symbols 0to uindicate the following.
0Serviceable with engine mounted
qFillingfluid
wLubricant
eSpecial tool
rTighteningtorque
tWear limit, clearance
yEngine speed
uElectrical data
Symbols ito gin the exploded diagrams indi-
cate the types of lubricants and lubrication
points.
iEngineoil
oGear oil
pMolybdenum-disulfideoil
aBrake fluid
sWheel-bearinggrease
dLithium-soap- based grease
fMolybdenum-disulfidegrease
gSilicone grease
Symbols hto jin the exploded diagrams indi-
cate the following.
hApply locking agent (LOCTITE®)
jReplace the part
T
R
.
.
t y u
LT
BF
opa
S
dfg
FI

EAS00011 TABLE OF CONTENTS
GENERAL INFORMATION
SPECIFICATIONS
PERIODIC CHECKS AND
ADJUSTMENTS
CHASSIS
ENGINE
FUEL INJECTION SYSTEM
ELECTRICAL SYSTEM
TROUBLESHOOTING
-+
GEN
INFO
SPEC
CHK
ADJ
CHAS
ENG
FI
ELEC
TRBL
SHTG
1
2
3
4
5
6
7
8

1-13
GEN
INFO
CHAPTER 1
GENERAL INFORMATION
SCOOTER IDENTIFICATION................................................................... 1-1
VEHICLE IDENTIFICATION NUMBER............................................. 1-1
MODEL LABEL..................................................................................1-1
FEATURES ............................................................................................... 1-2
OUTLINE OF THE FI SYSTEM......................................................... 1-2
FI SYSTEM ........................................................................................1-3
O2sensor............................................................................................1-4
IMPORTANT INFORMATION................................................................... 1-5
PREPARATION FOR REMOVAL AND DISASSEMBLY...................1-5
REPLACEMENT PARTS ................................................................... 1-5
GASKETS, OIL SEALS AND O-RINGS............................................1-5
LOCK WASHERS/PLATES AND COTTER PINS.............................1-6
BEARINGS AND OIL SEALS............................................................1-6
CIRCLIPS...........................................................................................1-6
EQUIPMENT PREPARATION........................................................... 1-7
CHECKING THE CONNECTIONS........................................................... 1-8
SPECIAL TOOLS......................................................................................1-9

1-1
GEN
INFO
SCOOTER IDENTIFICATION
EAS00015
GENERALINFORMATION
SCOOTER IDENTIFICATION
EAS00017
VEHICLE IDENTIFICATION NUMBER
The vehicle identification number 1is stamped
into the frame.
EAS00018
MODEL LABEL
The model label 1is affixed to the frame under
the seat.This information will be needed to or-
der spare parts.
1
1

1-2
GEN
INFO
EAS00896
FEATURES
OUTLINE OF THE FI SYSTEM
The main function of a fuel supply system is to provide fuel to the combustion chamber at the opti-
mum air-fuel ratio in accordance with the engine operating conditions and the atmospheric tempera-
ture. In the conventional carburetor system, the air-fuel ratio of the mixture that is supplied to the
combustion chamber is created by the volume of the intake air and the fuel that is metered by the jet
used in the respective carburetor.
Despite the same volume of intake air, the fuel volume requirement varies by the engine operating
conditions, such as acceleration, deceleration, or operation under a heavy load. Carburetors that
meter the fuel through the use of jets have been provided with various auxiliary devices, so that an
optimum air-fuel ratio can be achieved to accommodate the constant changes in the operating con-
ditions of the engine.
As the requirements for the engine to deliver more performance and cleaner exhaust gases in-
crease, it becomes necessary to control the air-fuel ratio in a more precise and finely tuned manner.
To accommodate this need, this model has adopted an electronically controlled fuel injection(FI)
system, in place of the conventional carburetor system.This system can achieve an optimum air-
fuel ratio required by the engine at all times by using a microprocessor that regulates the fuel injec-
tion volume according to the engine operating conditions detected by various sensors.
The adoption of the FI system has resulted in a highly precise fuel supply, improved engine re-
sponse, better fuel economy, and reduced exhaust emissions.
1ECU
2Engine trouble warning light
3Lean angle cut-off switch
4Fuel hose
5Ignitioncoil
6Fuel injector
7Intake air pressure sensor
8ISC(idle speed control) valve
9Intake air temperature sensor
0Battery
qAir filter case
wCatalytic converter
eCrankshaft position sensor
rEngine temperature sensor
tSpark plug
yFuel tank
uFuelpump
iThrottle position sensor
oO2sensor
FEATURES
q4 7
9
i
u
y8
61
2
30
t
ew
o
5
r

1-3
GEN
INFO
FEATURES
EAS00897
FI SYSTEM
The fuel pump delivers fuel to the fuel injector via the fuel filter.The pressure regulator maintains the
fuel pressure that is applied to the fuel injector at only 250 kPa (2.5 kgf/cm2, 35.6 psi). Accordingly,
when the energizing signal from the ECU energizes the fuel injector, the fuel passage opens, caus-
ing the fuel to be injected into the intake manifold only during the time the passage remains open.
Therefore, the longer the length of time the fuel injector is energized (injection duration), the greater
the volume of fuel that is supplied. Conversely, the shorter the length of time the fuel injector is
energized (injection duration), the lesser the volume of fuel that is supplied.
The injection duration and the injection timing are controlled by the ECU.Signals that are input from
the crankshaft position sensor, intake air pressure sensor, intake temperature sensor and engine
temperature sensor enable the ECU to determine the injection duration.The injection timing is deter-
mined through the signals from the crankshaft position sensor. As a result, the volume of fuel that is
required by the engine can be supplied at all times in accordance with the driving conditions.
1Fuelpump
2Fuel injector
3Ignitioncoil
4ECU
5Catalytic converter
6Engine temperature sensor
7Crankshaft position sensor
8Intake air pressure sensor
9Throttle body assembly
0Intake air temperature sensor
Illustration is for reference only.
qAir filter case
wISC (idle speed control) valve
eThrottle position sensor
rO2sensor
AFuel system
BAir system
CControl system
5
1A3
4
6
7
9
0
q
e
w
C
MAQS
B
8
REC./REG.
2
r

1-4
GEN
INFO
FEATURES
O2sensor
The O2sensor has been adopted to enable the catalyst to function at a high degree of efficiency by
maintaining the air-fuel mixture near the stoichiometric ratio (14.7:1).This sensor, which is a zirconia
type, utilizes the oxygen ion conductivity of the solid electrolyte for detecting the oxygen concentra-
tion levels. In actual operation, a zirconia tube made of solid electrolyte is exposed in the exhaust
gas, so that the exterior of the zirconia tube is in contact with the exhaust gas and the interior is in
contact with the atmosphere whose oxygen concentration level is known.When a difference in the
oxygen concentration level is created between the outside and the inside of the zirconia tube, the
oxygen ion passes through the zirconia element and generates an electromotive force.The electro-
motive force increases when the oxygen concentration level is low (rich air-fuel ratio) and the elec-
tromotive force decreases when the oxygen concentration level is high (lean air-fuel ratio). As elec-
tromotive force is generated in accordance with the concentration of the exhaust gas, the resultant
voltage is input into the ECU in order to correct the duration of the injection of fuel.
1Inner cover
2Outer cover
3Zirconia tube
4Exhaust gas
5Atmosphere
AAtmosphere
BInner electrode
CZirconiaelement
DOuter electrode
EPorous ceramic layer
FExhaust gas

1-5
GEN
INFO
IMPORTANT INFORMATION
EAS00020
IMPORTANT INFORMATION
PREPARATION FOR REMOVAL AND DISAS-
SEMBLY
1. Before removal and disassembly, remove
all dirt, mud, dust and foreign material.
2. Use only the proper tools and cleaning
equipment.
Refer to the “SPECIAL TOOLS”.
3. When disassembling, always keep mated
parts together. This includes gears, cylin-
ders,pistonsandotherpartsthat havebeen
“mated” through normal wear. Mated parts
must always be reused or replaced as an
assembly.
4. During disassembly, clean all of the parts
and place them in trays in the order of dis-
assembly.This will speed up assembly and
allow for the correct installation of all parts.
5. Keep all parts away from any source of fire.
EAS00021
REPLACEMENT PARTS
Use only genuineYamaha parts for all replace-
ments. Use oil and grease recommended by
Yamaha forall lubricationjobs.Otherbrandsmay
be similar in function and appearance, but infe-
rior in quality.
EAS00022
GASKETS, OIL SEALS AND O-RINGS
1. When overhauling the engine, replace all
gaskets, seals and O-rings. All gasket sur-
faces, oil seal lips and O-rings must be
cleaned.
2. During reassembly, properly oil all mating
parts andbearingsand lubricate theoil seal
lips with grease.

1-6
GEN
INFO
IMPORTANT INFORMATION
EAS00023
LOCK WASHERS/PLATES AND COTTER
PINS
After removal, replace all lock washers/plates
1andcotter pins.After thebolt ornut hasbeen
tightened to specification, bend the lock tabs
along a flat of the bolt or nut.
EAS00024
BEARINGS AND OIL SEALS
Install bearings and oil seals so that the
manufacturer’s marks or numbers are visible.
When installing oil seals, lubricate the oil seal
lips with a light coat of lithium-soap-based
grease. Oil bearings liberally when installing, if
appropriate.
1Oil seal
NOTICE
Do not spin the bearing with compressed
air because this will damage the bearing
surfaces.
1Bearing
EAS00025
CIRCLIPS
Before reassembly, check all circlips carefully
and replace damaged or distorted circlips. Al-
waysreplacepistonpinclips after oneuse.When
installingacirclip 1,makesurethesharp-edged
corner 2is positioned opposite the thrust 3
that the circlip receives.
4Shaft

1-7
GEN
INFO
IMPORTANT INFORMATION
EAS00021
EQUIPMENT PREPARATION
Turn Rivet (Turn type)
Assembly status of the turn rivet(turn type).
Dissembling
1. Press center pin1inward to release the
lock.
2. Remove the push rivet main body2.
Assembling
1. Restorethecenter pin,replacethe turnrivet
main body.
2. Turn in the center pin until leveling off with
the surface position of the turn rivet main
body.

1-8
GEN
INFO
CHECKING THE CONNECTIONS
EAS00026
CHECKING THE CONNECTIONS
Check the leads, couplers, and connectors for
stains, rust, moisture, etc.
1. Disconnect:
8lead
8coupler
8connector
2. Check:
8lead
8coupler
8connector
Moisture JDry with an air blower.
Rust/stains JConnect and disconnect
several times.
3. Check:
8all connections
Loose connection JConnect properly.
TIP
If the pin 1on the terminal is flattened, bend it
up.
4. Connect:
8lead
8coupler
8connector
TIP
Make sure all connections are tight.
5. Check:
8continuity
(with the pocket tester)
Pocket tester
90890-03112 (YU-03112-C)
TIP
8Ifthere isno continuity,clean the terminals.
8When checking the wire harness, perform
steps (1) to (3).
8Asa quickremedy, use acontact revitalizer
available at most part stores.

1-9
GEN
INFO
Tool NO. Tool name / Function Illustration
90890-01085(M8)
YU-01083-2
90890-01084
YU-01083-3
90890-01235
YU-01235
90890-01268
YU-01268
90890-01304
YU-01304
90890-01337
YM-33285
90890-01311
YM-08035-A
90890-01326
YM-01326
90890-01294
YM-01300-1
90890-01348
YM-01348
Slidehammerbolt(8mm)1
Weight2
Thesetoolsareneededtoremove the cam-
shaft.
Rotorholdingtool
This tool is used to hold the primary fixed
sheave and secondary sheave assembly.
Ringnutwrench
This tool is used to loosen and tighten the
exhaustandsteeringringnut.
Piston pin puller set
This tool is used to remove the piston pin.
Clutchspringholder
Thesetoolareusedforremovingthenut with
holdingthecompressionspring.
Valve adjusting tool
This tool is necessary for adjusting valve
clearance.
T-handle1
Damperrodholder2
Thesetoolsareused toholdthedamperrod
whenremovingorinstallingthe damperrod.
Locknutwrench
This tool is used when removing or install-
ing the secondary sheave nut.
SPECIAL TOOLS
1
2
12
EAS00027
SPECIAL TOOLS
The following special tools are necessary for complete and accurate tune-up and assembly. Use
only the appropriate special tools as this will help prevent damage caused by the use of inappropri-
ate tools or improvised techniques.Special tools, part numbers or both may differ depending on the
country.
When placing an order, refer to the list provided below to avoid any mistakes.
TIP
8For U.S.A. and Canada, use part number starting with "YM-", "YU-", or "ACC-".
8For others, use part number starting with "90890-".
41
46

1-10
GEN
INFO
Tool NO. Tool name / Function Illustration
SPECIAL TOOLS
90890-01189
YM-01189
90890-01367
YM-A9409-7
90890-01368
YM-A9409-4
90890-01384
YM-33299
90890-01403
YU-A9472
90890-01701
YS-01880-A
90890-03079
YM-34483
90890-03081
YU-33223
90890-03112
YU-03112-C
90890-03174
90890-06760
Flywheelpuller
This tool is used for removing the AC mag-
netorotor.
Fork seal driver weight 1
Forksealdriverattachment(Ø33mm)2
Thesetoolsare usedwheninstallingthe fork
seal.
Oil seal guide
This tool is used for protecting the oil seal
lip when installing the secondary sliding
sheave.
Steeringnutwrench
This tool is used to loosen and tighten the
steeringringnut.
Sheaveholder
This tool is used for holding the secondary
sheave.
Thicknessgauge
This tool is used to measure the valve
cleanance.
Compressiongauge
Thistoolis usedtomeasure theenginecom-
pression.
Pocket tester
This instrument is invaluable for checking
the electrical system.
Digital circuit tester
This instrument is invaluable for checking
the electrical system.
Digitaltachometer
Thistoolisneeded fordetectingenginerpm.
12

1-11
GEN
INFO
Tool NO. Tool name / Function Illustration
SPECIAL TOOLS
90890-03141
YU-03141
90890-04101
90890-04019
YM-04019
90890-04108
YM-04108
90890-04116
YM-04116
90890-04117
YM-04117
90890-04118
YM-04118
90890-06754
YM-34487
90890-03182
YU-03182
90890-03153
YU-03153
90890-03186
Timinglight
This tool is used to check the ignition tim-
ing.
Valvelapper
Thistoolisneededtoremove and installthe
valve lifters.
Valvespringcompressor
Compressoradapter(Ø19mm)
These tools are used when removing or in-
stalling the valve and the valve spring.
Valveguideremover(4.5mm)
This tool is used to remove or install the
valve guides.
Valveguideinstaller(4.5mm)
This tool is used to install the valve guides.
Valveguidereamer(4.5mm)
This tool is used to rebore the new valve
guides.
Ignitionchecker
This tool is used to check the ignition sys-
temcomponents.
FI diagnostic tool
ExecuteCOadjustment,confirmfaultcode,
self diagnosis tool.
Pressuregauge
This tool is used to measure fuel pressure.
Fuelpressureadapter
This tool is used to measure fuel pressure.

1-12
GEN
INFO
SPECIAL TOOLS
Tool NO. Tool name / Function Illustration
90890-85505
ACC-11001-05-01 YamahabondNO.1215 Sealant (Quick Gasket®)
This sealant (bond) is used to apply on
crankcase mating surfaces.

2-32
SPEC
CHAPTER 2
SPECIFICATIONS
GENERAL SPECIFICATIONS ................................................................. 2-1
ENGINE SPECIFICATIONS ..................................................................... 2-2
CHASSIS SPECIFICATIONS .................................................................2-12
ELECTRICAL SPECIFICATIONS..........................................................2-15
GENERAL TIGHTENING TORQUE SPECIFICATIONS .......................2-18
TIGHTENING TORQUES........................................................................2-19
ENGINE............................................................................................2-19
CHASSIS..........................................................................................2-21
LUBRICATION POINTS AND LUBRICANT TYPES.............................2-23
ENGINE............................................................................................2-23
CHASSIS..........................................................................................2-25
CABLE ROUTING ..................................................................................2-26