2009

MOTORCYCLE

SERVICE MANUAL

Model : YW125Y_

32SF819770E0 *32SF819770E0*

EAS00000

YW125Y 2009

SERVICE MANUAL

©2008 by Yamaha Motor Taiwan 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 the Yamaha Motor Taiwan Company, Ltd. primarily for use by Yamaha

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 on Yamaha

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 a Yamaha 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 Motor Taiwan 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.

A WARNING 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

HOW TO USE THIS 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.

1

The manual is divided into chapters. An abbreviation and symbol in the upper right corner of

each page indicate the current chapter.]

Refer to “SYMBOLS”.

2 Each 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.

3 Sub-section titles appear in smaller print than the section title.

4 To help identify parts and clarify procedure steps, there are exploded diagrams at the start of

each removal and disassembly section.

5 Numbers are given in the order of the jobs in the exploded diagram. A circled number indicates

a disassembly step.

6 Symbols indicate parts to be lubricated or replaced.

Refer to “SYMBOLS”.

7 A job instruction chart accompanies the exploded diagram, providing the order of jobs, names of

parts, notes in jobs, etc.

8 Jobs requiring more information (such as special tools and technical data) are described se-

quentially.

5-32

ENG

Remarks

Order

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”.

For installation, reverse the removal pro-

cedure.

1

1

2

1

2

1

1

1

CYLINDER AND PISTON

5

8

6

5

3

3

4

2

1

7

ENG

5-33

3

2

1

EAS00253

REMOVING THE 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

8 Before removing the piston pin clip, cover

the crankcase opening with a clean rag to

prevent the piston pin clip from falling into

the crankcase.

8 Before removing the piston pin, deburr the

piston pin clip’s groove and the piston’s pin

bore area.

8 If 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.

3

2

4

4

5

7

6 2

1

3

8

GEN

INFO

SPEC

CHK

ADJ

ENG

TRBL

SHTG

CHAS

-

+

ELEC

4

M

B

LS

New

M

G

COOL

1

2

3

4

5

6

7

8

9

0

q

w

e

r

i

s

h

j

EAS00008

SYMBOLS

The following symbols are not relevant to every

vehicle.

Symbols 1 to 9 indicate the subject of each

chapter.

1 General information

2 Specifications

3 Periodic checks and adjustments

4 Chassis

5 Engine

6 Cooling system

7 Fuel injection system

8 Electrical system

9 Troubleshooting

Symbols 0 to u indicate the following.

0 Serviceable with engine mounted

q Filling fluid

w Lubricant

e Special tool

r Tightening torque

t Wear limit, clearance

y Engine speed

u Electrical data

Symbols i to g in the exploded diagrams indi-

cate the types of lubricants and lubrication

points.

i Engine oil

o Gear oil

p Molybdenum-disulfide oil

a Brake fluid

s Wheel-bearing grease

d Lithium-soap- based grease

f Molybdenum-disulfide grease

g Silicone grease

Symbols h to j in the exploded diagrams indi-

cate the following.

h Apply locking agent (LOCTITE^®)

j Replace the part

T R

.

.

t y u

LT

BF

o

p

a

S

d

f

g

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

O2 sensor............................................................................................ 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

GENERAL INFORMATION

SCOOTER IDENTIFICATION

EAS00017

VEHICLE IDENTIFICATION NUMBER

The vehicle identification number 1 is stamped

into the frame.

EAS00018

MODEL LABEL

The model label 1 is 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.

1

ECU

2

Engine trouble warning light

3

Lean angle cut-off switch

4

Fuel hose

5

Ignition coil

6

Fuel injector

7

Intake air pressure sensor

8

ISC(idle speed control) valve

9

Intake air temperature sensor

0 Battery

q Air filter case

w Catalytic converter

e Crankshaft position sensor

r Engine temperature sensor

t Spark plug

y Fuel tank

u Fuel pump

i Throttle position sensor

o O2 sensor

FEATURES

q

4

7

9

i

u

y

8

6

1

2

3

0

t

e

w

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.

1

Fuel pump

2

Fuel injector

3

Ignition coil

4

ECU

5

Catalytic converter

6

Engine temperature sensor

7

Crankshaft position sensor

8

Intake air pressure sensor

9

Throttle body assembly

0

Intake air temperature sensor

Illustration is for reference only.

q

Air filter case

w

ISC (idle speed control) valve

e

Throttle position sensor

r

O2 sensor

A

Fuel system

B

Air system

C

Control system

5

1

A

3

4

6

7

9

0

q

e

w

C

MAQS

B

8

REC./REG.

2

r

1-4

GEN

INFO

FEATURES

O2 sensor

The O2 sensor 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.

1

Inner cover

2

Outer cover

3

Zirconia tube

4

Exhaust gas

5

Atmosphere

A

Atmosphere

B

Inner electrode

C

Zirconia element

D

Outer electrode

E

Porous ceramic layer

F

Exhaust 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, pistons and other parts that have been

“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 genuine Yamaha parts for all replace-

ments. Use oil and grease recommended by

Yamaha for all lubrication jobs. Other brands may

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 and bearings and lubricate the oil seal

lips with grease.

1-6

GEN

INFO

IMPORTANT INFORMATION

EAS00023

LOCK WASHERS/PLATES AND COTTER

PINS

After removal, replace all lock washers/plates

1 and cotter pins. After the bolt or nut has been

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.

1 Oil seal

NOTICE

Do not spin the bearing with compressed

air because this will damage the bearing

surfaces.

1 Bearing

EAS00025

CIRCLIPS

Before reassembly, check all circlips carefully

and replace damaged or distorted circlips. Al-

ways replace piston pin clips after one use. When

installing a circlip 1, make sure the sharp-edged

corner 2 is positioned opposite the thrust 3

that the circlip receives.

4 Shaft

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 pin1 inward to release the

lock.

2. Remove the push rivet main body2.

Assembling

1. Restore the center pin, replace the turn rivet

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 J Dry with an air blower.

Rust/stains J Connect and disconnect

several times.

3. Check:

8all connections

Loose connection J Connect properly.

TIP

If the pin 1 on 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

8 If there is no continuity, clean the terminals.

8 When checking the wire harness, perform

steps (1) to (3).

8 As a quick remedy, use a contact revitalizer

available at most part stores.