Yamaha YZ 125 User manual

B0V-28199-12LIT-11626-34-28
Read this manual carefully before operating this vehicle.
YZ125M2
OWNER’S MANUAL
YZ125
2021
PRINTED IN JAPAN
2020.05-0.4×1 !
(E)
B0V-28199-12_cover.indd 1-3 2020/04/30 14:40:38

Operating, servicing and
maintaining a passenger vehicle or off-road vehicle can
expose you to chemicals including engine exhaust,
carbon monoxide, phthalates, and lead, which are
known to the State of California to cause cancer and
birth defects or other reproductive harm. To minimize
exposure, avoid breathing exhaust, do not idle the
engine except as necessary, service your vehicle in a
well-ventilated area and wear gloves or wash your
hands frequently when servicing your vehicle. For more
information go to
www.P65Warnings.ca.gov/passenger-vehicle
QRead this manual carefully before operating this vehicle. This manual should stay with this vehicle
if it is sold.
EAM20160Genuine Yamaha Parts text
For your best ownership experience, think Genuine Yamaha!
Genuine Yamaha Parts – Genuine Yamaha replacement parts are the exact same parts as the ones
originally equipped on your vehicle, providing you with the performance and durability you have come
to expect. Why settle for aftermarket parts that may not provide full confidence and satisfaction?
Genuine Yamaha Accessories – Yamaha only offers accessories that meet our high standards for
quality and performance. Buy with confidence, knowing your Genuine Yamaha Accessories will fit right
and perform right – right out of the box.
Yamalube – Take care of your Yamaha with legendary Yamalube oils, lubricants, and care products.
They’re formulated and approved by the toughest judges we know: the Yamaha engineering teams that
know your Yamaha from the inside out.
Genuine Yamaha Service Manuals – Get the same factory manual for your vehicle that the techni-
cians at your authorized Yamaha dealer use. Service manuals are available through your Yamaha
dealer or you can order them directly through yamahapubs.com.
Genuine Yamaha products are available only from your Yamaha dealer.
Find out more at yamaha-motor.com
B0V-28199-12_cover.indd 4-6 2020/04/30 14:40:39

EAM20080
YZ125M2
OWNER’S MANUAL
©2021 by Yamaha Motor Corporation, U.S.A.
First edition, May 2020
All rights reserved.
Any reprinting or unauthorized use
without the written permission of
Yamaha Motor Corporation, U.S.A.
is expressly prohibited.
P/N. LIT-11626-34-28
Printed in Japan.

EAM20180
IMPORTANT
Congratulations on your purchase of a Yamaha YZ series. This model is the culmination of Yamaha’s
vast experience in the production of pacesetting racing machines. It represents the highest grade of
craftsmanship and reliability that have made Yamaha a leader.
This manual explains operation, inspection, basic maintenance and tuning of your machine. If you have
any questions about this manual or your machine, please contact your Yamaha dealer.
TIP
•Yamaha continually seeks advancements in product design and quality. Therefore, while this manual
contains the most current product information available at the time of printing, there may be minor dis-
crepancies between your machine and this manual. If you have any questions concerning this man-
ual, please consult your Yamaha dealer.
•This manual is intended for those who have basic knowledge and skill concerning the servicing of
Yamaha motorcycles (e.g., Yamaha dealers, service engineers, etc.). Those who have little knowl-
edge and skill concerning servicing are requested not to undertake inspection, adjustment, disassem-
bly, or reassembly only by reference to this manual. It may lead to servicing trouble and mechanical
damage.
WARNING
EWA20270
PLEASE READ THIS MANUAL CAREFULLY AND COMPLETELY BEFORE OPERATING THIS
MACHINE. DO NOT ATTEMPT TO OPERATE THIS MACHINE UNTIL YOU HAVE ATTAINED A
SATISFACTORY KNOWLEDGE OF ITS CONTROLS AND OPERATING FEATURES AND UNTIL
YOU HAVE BEEN TRAINED IN SAFE AND PROPER RIDING TECHNIQUES. REGULAR INSPEC-
TIONS AND CAREFUL MAINTENANCE, ALONG WITH GOOD RIDING SKILLS, WILL ENSURE
THAT YOU SAFETY ENJOY THE CAPABILITIES AND THE RELIABILITY OF THIS MACHINE.
EAM30001
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 per-
sonal 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.
WARNING
NOTICE
TIP

EAM20162
YAMAHA MOTOR CORPORATION, U.S.A. YZ MOTORCYCLE LIMITED
WARRANTY

GENERAL INFORMATION 1
SPECIFICATIONS 2
PERIODIC CHECKS AND
ADJUSTMENTS 3
CHASSIS 4
ENGINE 5
ELECTRICAL SYSTEM 6
TROUBLESHOOTING 7
TUNING 8
EAM10003
TABLE OF CONTENTS

1
2
3
4
5
6
7
8
9
10
GENERAL INFORMATION
SAFETY INFORMATION ..................................................................................1-1
FOR SAFETY, BE SURE TO OBEY THE FOLLOWING:...........................1-1
LOCATION OF IMPORTANT LABELS.............................................................1-4
DESCRIPTION..................................................................................................1-5
IDENTIFICATION ..............................................................................................1-6
VEHICLE IDENTIFICATION NUMBER ......................................................1-6
ENGINE SERIAL NUMBER........................................................................1-6
INCLUDED PARTS ...........................................................................................1-7
SIDESTAND ...............................................................................................1-7
NIPPLE WRENCH......................................................................................1-7
VALVE JOINT.............................................................................................1-7
COLLAR (tool for YPVS) ............................................................................1-7
IMPORTANT INFORMATION ...........................................................................1-8
PREPARATION FOR REMOVAL AND DISASSEMBLY............................1-8
REPLACEMENT PARTS............................................................................1-8
INSTRUMENT AND CONTROL FUNCTIONS .................................................1-9
ENGINE STOP SWITCH ............................................................................1-9
SHIFT PEDAL.............................................................................................1-9
KICKSTARTER LEVER..............................................................................1-9
FRONT BRAKE LEVER .............................................................................1-9
REAR BRAKE PEDAL................................................................................1-9
FUEL COCK ...............................................................................................1-9
STARTER KNOB (CHOKE)......................................................................1-10
STARTING AND BREAK-IN ...........................................................................1-11
FUEL AND ENGINE MIXING OIL.............................................................1-11
STARTING A COLD ENGINE ..................................................................1-11
STARTING A WARM ENGINE .................................................................1-11
BREAK-IN PROCEDURES ......................................................................1-11
MAINTENANCE AFTER BREAK-IN ..............................................................1-13
MAJOR MAINTENANCE ..........................................................................1-13
AIR FILTER MAINTENANCE ...................................................................1-13
TORQUE-CHECK POINTS.............................................................................1-14
MOTORCYCLE CARE AND STORAGE.........................................................1-16
CARE........................................................................................................1-16

STORAGE ................................................................................................1-17