Yamaha MBK MW125 2014 User manual

SERVICE MANUAL
MW125 2014
MW125F 2015
2CM-F8197-E0

EAS20002
MW125 2014
MW125F 2015
SERVICE MANUAL
©2014 by Thai Yamaha Motor Co.,Ltd.
First edition, May 2014
All rights reserved.
Any reproduction or unauthorized use
without the written permission of
Thai Yamaha Motor Co.,Ltd.
is expressly prohibited.

EAS20003
IMPORTANT
This manual was produced by the Thai Yamaha Motor Co., Ltd. primarily for use by Yamaha and MBK
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
and MBK 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.
Thai Yamaha Motor Co., Ltd. is continually striving to improve all of its models. Modifications and sig-
nificant changes in specifications or procedures will be forwarded to all authorized Yamaha and MBK
dealers and will appear in future editions of this manual where applicable.
TIP
Designs and specifications are subject to change without notice.
EAS30001
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 inju-
ry 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.
WARNING
NOTICE
TIP

EAS20004
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.
• The manual is divided into chapters and each chapter is divided into sections. The current section title
is shown at the top of each page “1”.
• Sub-section titles appear in smaller print than the section title “2”.
• To help identify parts and clarify procedure steps, there are exploded diagrams at the start of each
removal and disassembly section “3”.
• Numbers are given in the order of the jobs in the exploded diagram. A number indicates a disassembly
step “4”.
• Symbols indicate parts to be lubricated or replaced “5”.
Refer to “SYMBOLS”.
• A job instruction chart accompanies the exploded diagram, providing the order of jobs, names of parts,
notes in jobs, etc “6”.
This step explains removal procedure only. For installation, reverse the steps.
• Jobs requiring more information (such as special tools and technical data) are described sequentially
“7”.
1
7
3
5
4
6
2

EAS20005
SYMBOLS
The following symbols are used in this manual for easier understanding.
TIP
The following symbols are not relevant to every vehicle.
SYMBOL DEFINITION SYMBOL DEFINITION
Serviceable with engine mounted Gear oil
Filling fluid Molybdenum disulfide oil
Lubricant Brake fluid
Special tool Wheel bearing grease
Tightening torque Lithium-soap-based grease
Wear limit, clearance Molybdenum disulfide grease
Engine speed Silicone grease
Electrical data Apply locking agent (LOCTITE®).
Engine oil Replace the part with a new one.
G
M
BF
B
T
R
.
.
LS
M
S
LT
E
New

EAS10003 TABLE OF CONTENTS
GENERAL INFORMATION 1
SPECIFICATIONS 2
PERIODIC CHECKS AND
ADJUSTMENTS 3
CHASSIS 4
ENGINE 5
COOLING SYSTEM 6
FUEL SYSTEM 7
ELECTRICAL SYSTEM 8
TROUBLESHOOTING 9

1
GENERAL INFORMATION
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
INSTRUMENT FUNCTIONS .....................................................................1-4
IMPORTANT INFORMATION .........................................................................1-7
PREPARATION FOR REMOVAL AND DISASSEMBLY...........................1-7
REPLACEMENT PARTS...........................................................................1-7
GASKETS, OIL SEALS AND O-RINGS ....................................................1-7
LOCK WASHERS/PLATES AND COTTER PINS .....................................1-7
BEARINGS AND OIL SEALS ....................................................................1-8
CIRCLIPS ..................................................................................................1-8
RUBBER PARTS.......................................................................................1-8
BASIC SERVICE INFORMATION...................................................................1-9
QUICK FASTENERS.................................................................................1-9
ELECTRICAL SYSTEM...........................................................................1-10
SPECIAL TOOLS ..........................................................................................1-14

IDENTIFICATION
1-1
EAS20007
IDENTIFICATION
EAS30002
VEHICLE IDENTIFICATION NUMBER
The vehicle identification number “1” is stamped
into the frame.
EAS30003
MODEL LABEL
The model label “1” is affixed to the inside of the
storage compartment.
1
1

FEATURES
1-2
EAS20008
FEATURES
EAS30005
OUTLINE OF THE FI SYSTEM
The main function of a fuel supply system is to provide fuel to the combustion chamber at the optimum
air-fuel ratio in accordance with the engine operating conditions and the atmospheric temperature. 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 con-
ditions, such as acceleration, deceleration, or operating 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 conditions of the en-
gine.
As the requirements for the engine to deliver more performance and cleaner exhaust gases increase,
it becomes necessary to control the air-fuel ratio in a more precise and finely tuned manner. To accom-
modate 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 injection 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 response,
better fuel economy, and reduced exhaust emissions.
1
15 12 1113,14
9
6,7,8,
2,3 4 5
10
1. Engine trouble warning light
2. Lean angle sensor
3. Battery
4. Fuel pump
5. ECU (engine control unit)
6. Intake air temperature sensor
7. Intake air pressure sensor
8. Throttle position sensor
9. Crankshaft position sensor
10.Ignition coil
11. Spark plug
12. O2sensor
13. Coolant temperature sensor
14. Injector
15.Speed sensor

FEATURES
1-3
EAS30617
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 a certain level. Accordingly, when the energizing signal
from the ECU energizes the fuel injector, the fuel passage opens, causing 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
throttle position sensor, coolant temperature sensor, lean angle sensor, crankshaft position sensor, in-
take air pressure sensor, intake air temperature sensor, speed sensor and O2sensor enable the ECU
to determine the injection duration. The injection timing is determined 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
13
B
11
12
10
3
A
2
9
4
C6
5
7
8
1. Fuel pump
2. Injector
3. Coolant temperature sensor
4. ECU (engine control unit)
5. Throttle position sensor
6. Speed sensor
7. Lean angle sensor
8. Intake air temperature sensor
9. O2sensor
10.Crankshaft position sensor
11.Throttle body
12. Intake air pressure sensor
13.Air filter case
A. Fuel system
B. Air system
C. Control system

FEATURES
1-4
EAS30682
INSTRUMENT FUNCTIONS
Multi-function meter unit
WARNING
EWA12423
Be sure to stop the vehicle before making
any setting changes to the multi-function
meter unit. Changing settings while riding
can distract the operator and increase the
risk of an accident.
The multi-function meter unit is equipped with
the following:
• a speedometer
• a fuel meter
•aclock
• an outside air temperature display
• an odometer
• two tripmeters
• a fuel reserve tripmeter
• an oil change tripmeter
• a V-belt replacement tripmeter
• an oil change indicator
• a V-belt replacement indicator
TIP
• Be sure to turn the key to “ON” before using the
“SELECT” and “RESET” buttons.
• For the UK only: To switch the speedometer
and odometer/tripmeter displays between kilo-
meters and miles, press the “SELECT” button
for at least one second.
• If the coolant temperature warning light and
engine trouble warning light remain on during
the initial display mode, have the battery
charged by a Yamaha dealer.
Speedometer
The speedometer shows the vehicle’s traveling
speed.
Fuel meter
The fuel meter indicates the amount of fuel in the
fuel tank. The display segments of the fuel meter
disappear towards “E” (Empty) as the fuel level
decreases. When the bottom segment of the fuel
meter and fuel level warning indicator “ ” start
flashing, refuel as soon as possible. When the
key is turned to “ON”, all of the display segments
of the fuel meter will appear for a few seconds,
and then the fuel meter shows the actual fuel
level.
TIP
This fuel meter is equipped with a self-diagnosis
system. If a problem is detected in an electrical
circuit, all the display segments and fuel level
warning indicator start flashing. If this occurs,
check the electrical circuit.
Refer to “SIGNALING SYSTEM” on page 8-19.
1. Clock
2. “SELECT” button
3. Fuel level warning indicator “ ”
4. Fuel meter
5. Speedometer
6. “RESET” button
7. Outside air temperature display
8. Odometer/tripmeters
9. Oil change indicator “OIL CHANGE”
10.V-belt replacement indicator “V-BELT”
1 2 3 4 75 6
8910
1. Speedometer
1. Fuel level warning indicator “ ”
2. Fuel meter
1
1
2

FEATURES
1-5
Clock
[To set the clock]
1. Push the “SELECT” button and “RESET” but-
ton together for at least two seconds.
2. When the hour digits start flashing, push the
“RESET” button to set the hours.
3. Push the “SELECT” button, and the minute
digits will start flashing.
4. Push the “RESET” button to set the minute
digits.
5. Push the “SELECT” button and then release
it to start the clock.
Outside air temperature display “OUT
TEMP”
This display shows the outside air temperature
from –10 °C to 40 °C in 1 °C increments. The
temperature displayed may vary from the actual
outside air temperature.
TIP
• If the outside air temperature falls below –10
°C, a lower temperature than –10 °C will not be
displayed.
• If the outside air temperature climbs above 40
°C, a higher temperature than 40 °C will not be
displayed.
• The accuracy of the temperature reading may
be affected when riding slowly [approximately
under 20 km/h (12 mi/h)] or when stopped at
traffic signals, railroad crossings, etc.
Odometer and tripmeter modes
Push the “SELECT” button to switch the display
between the odometer mode “ODO”, the tripme-
ter modes “TRIP 1” and “TRIP 2”, the oil change
tripmeter mode “OIL TRIP” and the V-belt re-
placement tripmeter mode “BELT TRIP” in the
following order:
ODO →TRIP 1 →TRIP 2 →OIL TRIP →BELT
TRIP →ODO
When approximately 1.6 L (0.42 US gal, 0.35
Imp.gal of fuel remains in the fuel tank, the bot-
tom segment of the fuel meter and fuel level
warning indicator will start flashing, and the dis-
play will automatically change to the fuel reserve
tripmeter mode “F” and start counting the dis-
tance traveled from that point. In this case, push-
ing the “SELECT” button switches the display
between the various tripmeter and odometer
modes in the following order:
F →TRIP 1 →TRIP 2 →OIL TRIP →BELT
TRIP →ODO →F
To reset tripmeters 1, 2, or the fuel reserve trip-
meter, select it by pushing the “SELECT” button,
and then push the “RESET” button for at least
one second. If you do not reset the fuel reserve
tripmeter manually, it will reset itself automatical-
ly and the display will return to the prior mode af-
ter refueling and traveling 5 km (3 mi).
To reset the oil change tripmeter or V-belt re-
placement tripmeter, select it by pushing the
“SELECT” button, and then push the “RESET”
button for three to four seconds.
1. Clock
1. Outside air temperature display
1
1
1. Odometer/tripmeters
1

FEATURES
1-6
Oil change indicator “OIL CHANGE”
This indicator will come on at the initial 1000 km
(600 mi), then at 4000 km (2500 mi) and every
4000 km (2500 mi) thereafter to indicate that the
engine oil should be changed.
After changing the engine oil, reset the oil
change indicator and the oil change tripmeter.
To reset them both, select the oil change tripme-
ter, and then push the “RESET” button for one
second. While “OIL CHANGE” is flashing, push
the “RESET” button for three seconds. The oil
change tripmeter will be reset and the oil change
indicator will go off.
If the engine oil is changed before the oil change
indicator comes on (i.e., before the periodic oil
change interval has been reached), the oil
change tripmeter must be reset for the next peri-
odic oil change to be indicated at the correct
time.
TIP
If the oil change tripmeter is reset before the ini-
tial 1000 km (600 mi), the next periodic oil
change interval will be at every 4000 km (2500
mi) thereafter.
V-belt replacement indicator “V-BELT”
This indicator come on at every 20000 km
(12500 mi) to indicate that the V-belt should be
replaced.
If the V-belt replacement indicator has come on,
after replacing the V-belt, reset the V-belt re-
placement indicator and the V-belt replacement
tripmeter. To reset them both, select the V-belt
replacement tripmeter, and then push the “RE-
SET” button for one second. While “V-BELT” is
flashing, push the “RESET” button for three to
four seconds. The V-belt replacement tripmeter
will be reset and the V-belt replacement indica-
tor will go off.
If the V-belt is replaced before the V-belt re-
placement indicator comes on (i.e., before the
periodic V-belt replacement interval has been
reached), the V-belt replacement tripmeter must
be reset for the next periodic V-belt replacement
to be indicated at the correct time.
1. Oil change indicator “OIL CHANGE”
2. Oil change tripmeter
1. V-belt replacement indicator “V-BELT”
2. V-belt replacement tripmeter
1 2
1 2

IMPORTANT INFORMATION
1-7
EAS20009
IMPORTANT INFORMATION
EAS30006
PREPARATION FOR REMOVAL AND
DISASSEMBLY
1. Before removal and disassembly, remove all
dirt, mud, dust and foreign material.
2. Use only the proper tools and cleaning equip-
ment.
Refer to “SPECIAL TOOLS” on page 1-14.
3. When disassembling, always keep mated
parts together. This includes gears, cylinders,
pistons and other parts that have been “mat-
ed” through normal wear. Mated parts must
always be reused or replaced as an assem-
bly.
4. During disassembly, clean all of the parts and
place them in trays in the order of disassem-
bly. This will speed up assembly and allow for
the correct installation of all parts.
5. Keep all parts away from any source of fire.
EAS30007
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
inferior in quality.
EAS30008
GASKETS, OIL SEALS AND O-RINGS
1. When overhauling the engine, replace all
gaskets, seals and O-rings. All gasket surfac-
es, 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.
EAS30009
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.
1. Oil
2. Lip
3. Spring
4. Grease

IMPORTANT INFORMATION
1-8
EAS30010
BEARINGS AND OIL SEALS
Install bearings “1” and oil seals “2” 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.
NOTICE
ECA13300
Do not spin the bearing with compressed air
because this will damage the bearing surfac-
es.
EAS30011
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.
EAS30012
RUBBER PARTS
Check rubber parts for deterioration during in-
spection. Some of the rubber parts are sensitive
to gasoline, flammable oil, grease, etc. Do not al-
low any items other than the specified one to
contact the parts.

BASIC SERVICE INFORMATION
1-9
EAS20010
BASIC SERVICE INFORMATION
EAS30013
QUICK FASTENERS
Rivet type
1. Remove:
• Quick fastener
TIP
To remove the quick fastener, push its pin with a
screwdriver, then pull the fastener out.
2. Install:
• Quick fastener
TIP
To install the quick fastener, push its pin so that
it protrudes from the fastener head, then insert
the fastener into the part to be secured and push
the pin in with a screwdriver. Make sure that the
pin is flush with the fastener’s head.
Screw type
1. Remove:
• Quick fastener
TIP
To remove the quick fastener, loosen the screw
with a screwdriver, then pull the fastener out.
2. Install:
• Quick fastener
TIP
To install the quick fastener, insert the fastener
into the part to be secured and tighten the screw.

BASIC SERVICE INFORMATION
1-10
EAS30014
ELECTRICAL SYSTEM
Electrical parts handling
NOTICE
ECA16600
Never disconnect a battery lead while the en-
gine is running; otherwise, the electrical
components could be damaged.
NOTICE
ECA16751
When disconnecting the battery leads from
the battery, be sure to disconnect the nega-
tive battery lead first, then the positive bat-
tery lead. If the positive battery lead is
disconnected first and a tool or similar item
contacts the vehicle, a spark could be gener-
ated, which is extremely dangerous.
TIP
If a battery lead is difficult to disconnect due to
rust on the battery terminal, remove the rust us-
ing hot water.
NOTICE
ECA16760
Be sure to connect the battery leads to the
correct battery terminals. Reversing the bat-
tery lead connections could damage the
electrical components.
NOTICE
ECA16771
When connecting the battery leads to the
battery, be sure to connect the positive bat-
tery lead first, then the negative battery lead.
If the negative battery lead is connected first
and a tool or similar item contacts the vehi-
cle while the positive battery lead is being
connected, a spark could be generated,
which is extremely dangerous.
NOTICE
ECA16610
Turn the main switch to “OFF” before dis-
connecting or connecting an electrical com-
ponent.

BASIC SERVICE INFORMATION
1-11
NOTICE
ECA16620
Handle electrical components with special
care, and do not subject them to strong
shocks.
NOTICE
ECA16630
Electrical components are very sensitive to
and can be damaged by static electricity.
Therefore, never touch the terminals and be
sure to keep the contacts clean.
TIP
When resetting the ECU by turning the main
switch to “OFF”, be sure to wait approximately 5
seconds before turning the main switch back to
“ON”.
Checking the electrical system
TIP
Before checking the electrical system, make
sure that the battery voltage is at least 12 V.
NOTICE
ECA14371
Never insert the tester probes into the cou-
pler terminal slots. Always insert the probes
from the opposite end “a” of the coupler, tak-
ing care not to loosen or damage the leads.
NOTICE
ECA16640
For waterproof couplers, never insert the
tester probes directly into the coupler. When
performing any checks using a waterproof
coupler, use the specified test harness or a
suitable commercially available test har-
ness.
a