Yamaha YZ125X 2021 Application guide

Read this manual carefully before operating this vehicle.
2021
OWNER’S SERVICE MANUAL
YZ125X
YZ125XM
LIT-11626-34-08 B1B-2819U-10

EAM20161Read this manual carefully
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
Read this manual carefully before operating this vehicle. This manual should stay with this vehicle
if it is sold.

EAM20080
YZ125XM
OWNER’S SERVICE MANUAL
©2021 by Yamaha Motor Corporation, U.S.A.
First edition, March 2020
All rights reserved.
Any reproduction or unauthorized use
without the written permission of
Yamaha Motor Corporation, U.S.A.
is expressly prohibited.
P/N. LIT-11626-34-08

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.
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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

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

EAM20082
HOW TO USE THIS MANUAL
In this manual, descriptions of installation, removal, disassembly, assembly, check, and adjustment
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
“1” is shown at the top of each page.
•Sub-section titles “2” appear in smaller print than the section title.
•To help identify parts and clarify procedure steps, there are exploded diagrams “3” at the start of each
removal and disassembly section.
•Numbers “4” are given in the order of the jobs in the exploded diagram. A number indicates a removal
or a disassembly step.
•Symbols “5” indicate parts to be lubricated or replaced.
Refer to “SYMBOLS”.
•A job instruction chart “6” accompanies the exploded diagram, providing the order of jobs, the names
of parts, the notes in jobs, etc. This step explains removal and disassembly procedure only. For in-
stallation and assembly procedure, reverse the steps.
•Jobs “7” requiring more information (such as special tools and technical data) are described sequen-
tially.
1
7
3
5
4
6
2
G088877

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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

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
TUNING
10
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TABLE OF CONTENTS