Yamaha YZ125 Owner's Manual
  1. Manuals
  2. Brands
  3. Yamaha Manuals
  4. Motorcycle
  5. YZ 125
  6. Owner's manual

Yamaha YZ125 Owner's Manual

Hide thumbs Also See for YZ125:
Table of Contents

Advertisement

Quick Links

2021
OWNER'S MANUAL
YZ125
Read this manual carefully before operating this vehicle.
YZ125M2
LIT-11626-34-28
B0V-28199-12

Advertisement

Table of Contents
loading

Related Manuals for Yamaha YZ125

Summary of Contents for Yamaha YZ125

  • Page 1 2021 OWNER’S MANUAL YZ125 Read this manual carefully before operating this vehicle. YZ125M2 LIT-11626-34-28 B0V-28199-12...
  • Page 2 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...
  • Page 3 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.
  • Page 4 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.
  • Page 5 EAM20162 YAMAHA MOTOR CORPORATION, U.S.A. YZ MOTORCYCLE LIMITED WARRANTY...

  • Page 7: Table Of Contents

    TABLE OF CONTENTS EAM10003 GENERAL INFORMATION SPECIFICATIONS PERIODIC CHECKS AND ADJUSTMENTS CHASSIS ENGINE ELECTRICAL SYSTEM TROUBLESHOOTING TUNING...
  • Page 9 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...
  • Page 10 STORAGE ....................1-17...

  • Page 11: Safety Information

    Yamaha ma- accidents. Many accidents have been chine, and take care to maintain it properly and caused by an automobile driver who did not operate it safely.
  • Page 12 1. Always wear an approved helmet. Yamaha can neither endorse nor recommend 2. Wear a face shield or goggles. Wind in your the use of accessories not sold by Yamaha or unprotected eyes could contribute to an im- modifications not specifically recommended by...
  • Page 13 SAFETY INFORMATION Aftermarket Tires and Rims The tires and rims that came with your motorcy- cle were designed to match the performance ca- pabilities and to provide the best combination of handling, braking, and comfort. Other tires, rims, sizes, and combinations may not be appropriate. Refer to “CHECKING THE TIRES”...

  • Page 14: Location Of Important Labels

    LOCATION OF IMPORTANT LABELS EAM20085 LOCATION OF IMPORTANT LABELS Please read the following important labels carefully before operating this vehicle. 3, 4...

  • Page 15: Description

    DESCRIPTION EAM20086 DESCRIPTION 13 14 15 11 10 11.Check bolt (Transmission oil level) 1. Clutch lever 12.Rear brake pedal 2. Engine stop switch 13.Valve joint 3. Front brake lever 4. Throttle grip 14.Fuel cock 15.Air filter 5. Radiator cap 6. Fuel tank cap 16.Drive chain 17.Shift pedal 7.

  • Page 16: Identification

    There are two significant reasons for knowing the serial number of your vehicle: 1. When ordering parts, you can give the num- ber to your Yamaha dealer for positive identi- fication of the model you own. 2. If your vehicle is stolen, the authorities will need the number to search for and identify your vehicle.

  • Page 17: Included Parts

    INCLUDED PARTS EAM20088 INCLUDED PARTS EAM30372 SIDESTAND This sidestand “1” is used to support only the machine when standing or transporting it. EWA20260 WARNING • Never apply additional force to the sides- tand. • Remove this sidestand before starting out. EAM30615 COLLAR (tool for YPVS) This collar “1”...

  • Page 18: Important Information

    YAMAHA genuine Refer to “CARE” on page 1-16. parts and recommended parts.

  • Page 19: Instrument And Control Functions

    INSTRUMENT AND CONTROL FUNCTIONS EAM20181 INSTRUMENT AND CONTROL FUNCTIONS EAM30182 ENGINE STOP SWITCH The engine stop switch “1” is located on the left handlebar. Continue pushing the engine stop switch till the engine comes to a stop. EAM30188 FRONT BRAKE LEVER The front brake lever “1”...

  • Page 20: Starter Knob (Choke)

    INSTRUMENT AND CONTROL FUNCTIONS in this position. EAM30444 STARTER KNOB (CHOKE) When cold, the engine requires a richer air-fuel mixture for starting. A separate starter circuit, which is controlled by the starter knob “1”, sup- plies this mixture. Pull the starter knob out to open the circuit for starting.

  • Page 21: Starting And Break-In

    STARTING AND BREAK-IN 4. Run the engine at idle or slightly higher until it EAM20123 STARTING AND BREAK-IN warms up: this usually takes about one or two minutes. EAM30538 5. The engine is warmed up when it responds FUEL AND ENGINE MIXING OIL normally to the throttle with the starter knob Mix oil with the gas at the ratio specified below.
  • Page 22 STARTING AND BREAK-IN ECA25821 NOTICE After a break-in or after each race, always check the points shown in “TORQUE- CHECK POINTS” for tightening torques and retighten them. Also when the following parts are replaced, a break-in is required. • Cylinder and Crankshaft: A break-in is re- quired for about an hour.

  • Page 23: Maintenance After Break-In

    Disassemble the carburetor and clean the AIR FILTER MAINTENANCE small holes, blowing them with compressed Apply the Yamaha foam air filter oil or other qual- air. ity foam air filter oil to the element. (Excess oil in • CDI magneto...

  • Page 24: Torque-Check Points

    TORQUE-CHECK POINTS EAM20125 TORQUE-CHECK POINTS Frame construction Combined seat and fuel tank Fuel tank to frame Frame to rear frame Engine mounting Frame to engine Engine bracket to engine Engine bracket to frame Seat Seat to frame Steering Steering stem to handlebar Steering stem to frame Steering stem to upper bracket Upper bracket to handlebar...
  • Page 25 TORQUE-CHECK POINTS Plastic cover Tightening of front fender Tightening of fork leg protector Tightening of air scoop Left cover to rear frame Tightening of side cover Tightening of rear fender Tightening of mud flap Tightening of rear brake disc cover Tightening of rear brake caliper cover Concerning the tightening torque, refer to “TIGHTENING TORQUES”...

  • Page 26: Motorcycle Care And Storage

    MOTORCYCLE CARE AND STORAGE ucts are used on hard-to-remove dirt, do EAM20126 MOTORCYCLE CARE AND STOR- not leave the cleaner on the affected area any longer than instructed. Also, thorough- ly rinse the area off with water, immediately dry it, and then apply a corrosion protec- EAM30200 CARE tion spray.
  • Page 27 Salt sprayed on roads in the winter may remain well into spring. • Consult a Yamaha dealer for advice on what 1. Clean the motorcycle with cold water and a products to use.
  • Page 28 MOTORCYCLE CARE AND STORAGE stored. Long-term Before storing your motorcycle for several months: 1. Follow all the instructions in “CARE” on page 1-16. 2. Drain the fuel tank, fuel lines, and the carbu- retor float bowl. 3. Perform the following steps to protect the cyl- inder, piston rings, etc.

  • Page 29: Specifications

    SPECIFICATIONS GENERAL SPECIFICATIONS ................2-1 ENGINE SPECIFICATIONS................2-2 CHASSIS SPECIFICATIONS................2-4 TIGHTENING TORQUES..................2-7 GENERAL TIGHTENING TORQUE SPECIFICATIONS ......2-7 ENGINE TIGHTENING TORQUES ............2-8 CHASSIS TIGHTENING TORQUES ............2-9...

  • Page 30: General Specifications

    GENERAL SPECIFICATIONS EAM20127 GENERAL SPECIFICATIONS Model Model B0VA Dimensions Overall length 2135 mm (84.1 in) Overall width 825 mm (32.5 in) Overall height 1295 mm (51.0 in) Seat height 975 mm (38.4 in) Wheelbase 1445 mm (56.9 in) Ground clearance 365 mm (14.37 in) Weight Curb weight...

  • Page 31: Engine Specifications

    ENGINE SPECIFICATIONS EAM20128 ENGINE SPECIFICATIONS Engine Combustion cycle 2-stroke Cooling system Liquid cooled Induction system Reed valve Displacement 125 cm³ Number of cylinders Single cylinder Bore  stroke 54.0  54.5 mm (2.13  2.15 in) Compression ratio 8.6–10.7 : 1 Starting system Kickstarter Fuel...
  • Page 32 3.692 (48/13) Final drive Chain Air filter Air filter element Wet element Air filter oil grade Yamaha foam air filter oil or other quality foam air filter oil Carburetor Type  quantity TMXx38  1 ID mark 1C37 51 Main jet...

  • Page 33: Chassis Specifications

    Fork spring free length limit 449.0 mm (17.68 in) Inner tube bending limit 0.2 mm (0.01 in) Recommended oil Yamaha Suspension Oil S1 Quantity (left) 510.0 cm³ (17.24 US oz, 17.99 Imp.oz) Quantity (right) 510.0 cm³ (17.24 US oz, 17.99 Imp.oz)
  • Page 34 CHASSIS SPECIFICATIONS Adjustment value from the start position (Hard) Compression damping Adjusting system Mechanical adjustable type Unit for compression damping adjustment Click Adjustment value from the start position (Soft) Adjustment value from the start position (STD) Adjustment value from the start position (Hard) Rear suspension Type...
  • Page 35 CHASSIS SPECIFICATIONS Drive chain slack (Maintenance stand) 48.0–58.0 mm (1.89–2.28 in) 15-link length limit 242.9 mm (9.56 in)

  • Page 36: Tightening Torques

    TIGHTENING TORQUES EAM20131 TIGHTENING TORQUES EAM30205 GENERAL TIGHTENING TORQUE SPECIFICATIONS This chart specifies tightening torques for stan- dard fasteners with a standard ISO thread pitch. Tightening torque specifications for special com- ponents or assemblies are provided for each chapter of this manual. To avoid warpage, tight- en multi-fastener assemblies in a crisscross pat- tern and progressive stages until the specified tightening torque is reached.
  • Page 37 TIGHTENING TORQUES EAM30203 ENGINE TIGHTENING TORQUES - marked portion shall be checked for torque tightening after break-in or before each race. Thread Item Q’ty Tightening torques Remarks size Spark plug M14S 20 N·m (2.0 kgf·m, 15 lb·ft) Cylinder head nut 28 N·m (2.8 kgf·m, 21 lb·ft) Cylinder head stud bolt 13 N·m (1.3 kgf·m, 9.6 lb·ft)
  • Page 38 TIGHTENING TORQUES Thread Item Q’ty Tightening torques Remarks size Oil check bolt 10 N·m (1.0 kgf·m, 7.4 lb·ft) Oil drain bolt 20 N·m (2.0 kgf·m, 15 lb·ft) Kickstarter lever 10 N·m (1.0 kgf·m, 7.4 lb·ft) Clutch cover bolt 10 N·m (1.0 kgf·m, 7.4 lb·ft) Primary drive gear bolt 48 N·m (4.8 kgf·m, 35 lb·ft) Use a lock...
  • Page 39 TIGHTENING TORQUES Thread Item Q’ty Tightening torques Remarks size Inner tube and adjuster 55 N·m (5.5 kgf·m, 41 lb·ft) Base valve (front fork) 29 N·m (2.9 kgf·m, 21 lb·ft) Adjuster (damper assembly) 29 N·m (2.9 kgf·m, 21 lb·ft) Bleed screw (front fork) 1.3 N·m (0.13 kgf·m, 0.95 lb·ft) Front fork protector bolt 5 N·m (0.5 kgf·m, 3.7 lb·ft)
  • Page 40 TIGHTENING TORQUES Thread Item Q’ty Tightening torques Remarks size Nipple (spoke) — 2.5 N·m (0.25 kgf·m, 1.8 lb·ft)  Rear wheel sprocket nut 42 N·m (4.2 kgf·m, 31 lb·ft)  Rear brake disc cover bolt 10 N·m (1.0 kgf·m, 7.4 lb·ft) ...
  • Page 41 TIGHTENING TORQUES Thread Item Q’ty Tightening torques Remarks size Screw (mud flap) — 1.3 N·m (0.13 kgf·m, 0.95 lb·ft)  Side cover bolt 7 N·m (0.7 kgf·m, 5.2 lb·ft)  Seat bolt 19 N·m (1.9 kgf·m, 14 lb·ft)  Number plate bolt 7 N·m (0.7 kgf·m, 5.2 lb·ft) ...
  • Page 42 TIGHTENING TORQUES 2-13...

  • Page 43: Periodic Checks And Adjustments

    PERIODIC CHECKS AND ADJUSTMENTS MAINTENANCE INTERVALS ................3-1 MAINTENANCE INTERVALS..............3-1 PRE-OPERATION INSPECTION AND MAINTENANCE .........3-4 GENERAL INSPECTION AND MAINTENANCE ........3-4 ENGINE......................3-5 ADJUSTING THE PILOT AIR SCREW ............3-5 CHECKING THE ENGINE IDLING SPEED..........3-5 CHECKING THE THROTTLE GRIP ............3-5 CHECKING THE SPARK PLUG..............3-5 CHECKING THE TRANSMISSION OIL LEVEL .........3-6 CHANGING THE TRANSMISSION OIL .............3-6 ADJUSTING THE CLUTCH LEVER FREE PLAY ........3-7...
  • Page 44 LUBRICATING THE CLUTCH LEVER .............3-24 LUBRICATING THE PEDAL..............3-24...

  • Page 45: Maintenance Intervals

    (e.g., rain, dirt, etc.). Therefore, earlier inspection is required by reference to the list below. Items marked with an asterisk should be performed by a Yamaha dealer as they require special tools, data and technical skills.
  • Page 46  • Check chain slack, alignment and condition.   • Adjust and thoroughly lubricate 16 * Drive chain chain with Yamaha chain and cable lube or equivalent.  • Replace. • Check coolant level and for leak-  ...
  • Page 47 MAINTENANCE INTERVALS Every Every Every After race third race fifth race Item Routine break-in (about 2.5 (about 7.5 (about 12.5 required hours) hours) hours) • Check operation and for oil leak- age. • Adjust if necessary.   • Clean dust seal and lubricate with lithium-soap-based grease.

  • Page 48: Pre-Operation Inspection And Maintenance

    PRE-OPERATION INSPECTION AND MAINTENANCE EAM20134 PRE-OPERATION INSPECTION AND MAINTENANCE Before riding for break-in operation, practice or a race, make sure the machine is in good operating con- dition. Before using this machine, check the following points. EAM30209 GENERAL INSPECTION AND MAINTENANCE Item Inspect Page...

  • Page 49: Engine

    ENGINE EAM20135 EAM30475 ENGINE CHECKING THE THROTTLE GRIP Prior to adjusting throttle grip free play, the en- EAM30607 ADJUSTING THE PILOT AIR SCREW gine idling speed should be adjusted. 1. Adjust: 1. Check: • Pilot air screw “1” • Throttle grip free play “a” Out of specification ...

  • Page 50: Checking The Transmission Oil Level

    ENGINE utes and wait for five minutes. ECA13330 NOTICE 2. Place the machine on a level place and hold Before removing the spark plug, blow away it up on upright position by placing the main- any dirt accumulated in the spark plug well tenance stand under the engine.

  • Page 51: Adjusting The Clutch Lever Free Play

    ENGINE Out of specification  Regulate. 4. Remove: • Oil drain bolt “1” Clutch lever free play • Oil filler cap “2” 7.0–12.0 mm (0.28–0.47 in) G088887 2. Adjust: • Clutch lever free play Handlebar side a. Turn the adjuster “1” until the specified clutch lever free play is obtained.

  • Page 52: Adjusting The Clutch Lever Position

    4. Check: • Air filter element Damage  Replace. 5. Apply: 2. Tighten: Yamaha foam air filter oil or other quality • Locknut foam air filter oil. a. Put the air filter element into a plastic bag Locknut (clutch lever position) and drip the filter oil into the bag.

  • Page 53: Checking The Carburetor Joint

    ENGINE 6. Install: ECA26420 NOTICE • Air filter guide “1” Make sure that the air filter element is prop- erly seated in the air filter case. The engine Align the projection “a” on filter guide with the should never be operated without the air fil- hole “b”...

  • Page 54: Checking The Exhaust System

    ENGINE 5. Check: EAM30221 • Gasket “1” CHECKING THE EXHAUST SYSTEM Damage  Replace. 1. Remove: • Exhaust pipe • Silencer Install the gaskets with their depressed “a” fac- ing outward. 2. Check: • Exhaust pipe • Silencer Crack/damage  Replace. 3.

  • Page 55: Checking The Cooling System

    ENGINE do not remove the radiator cap when the en- 5. Check: gine is hot. Scalding hot fluid and steam may • Coolant level be blown out, which could cause serious in- jury. When the engine has cooled, open the Before checking the coolant level, wait a few radiator cap as follows: minutes until the coolant has settled.
  • Page 56 ENGINE Slowly loosen the radiator cap to drain cool- down. ant. 9. Check: • Coolant level When the radiator cap is loosened, coolant will Refer to “CHECKING THE COOLANT LEV- gush out transversely; therefore, bring the con- EL” on page 3-10. tainer near to the outlet.

  • Page 57: Chassis

    CHASSIS air must be removed by bleeding the brake EAM20136 CHASSIS system. Air in the brake system will consid- erably reduce braking performance. EAM30479 ADJUSTING THE FRONT DISC BRAKE ECA13490 NOTICE There should be no free play at the brake lever After adjusting the brake lever position, end.

  • Page 58: Checking The Brake Fluid Level

    CHASSIS c. Tighten the locknut to specification. A. Front brake B. Rear brake Rear brake pedal adjusting lock- EWA13090 6 N·m (0.6 kgf·m, 4.4 lb·ft) WARNING • Use only the designated brake fluid. Other EWA19150 brake fluids may cause the rubber seals to WARNING deteriorate, causing leakage and poor A soft or spongy feeling in the brake pedal...

  • Page 59: Checking The Rear Brake Pads

    CHASSIS 3. Hold the vehicle upright and apply the rear brake several times. 4. Check: • Brake hose Brake fluid leakage  Replace the damaged hose. EAM30499 CHECKING THE BRAKE OPERATION 1. Check: • Brake operation Brake not working properly  Check the EAM30232 CHECKING THE REAR BRAKE PADS brake system.

  • Page 60: Drive Chain Slack

    CHASSIS Brake caliper bleed screw 6 N·m (0.6 kgf·m, 4.4 lb·ft) j. Pour brake fluid to the reservoir up to the specified level. Refer to “CHECKING THE BRAKE FLUID LEVEL” on page 3-14. EWA13110 WARNING After bleeding the hydraulic brake system, check the brake operation.

  • Page 61: Checking And Adjusting The Steering Head

    CHASSIS gently rock the front fork. Drive chain slack (Maintenance Blinding/looseness  Adjust the steering stand) head. 48.0–58.0 mm (1.89–2.28 in) 3. Remove: • Handlebar Adjusting the drive chain slack • Upper bracket EWA13120 4. Adjust: WARNING • Steering head Securely support the vehicle so that there is a.

  • Page 62: Lubricating The Steering Head

    If any damage is found or the front fork does not per and lower bearings. operate smoothly, have a Yamaha dealer check Refer to “STEERING HEAD” on page or repair it. 4-24.

  • Page 63: Adjusting The Front Fork Legs

    CHASSIS Direction “a” Rebound damping is increased (sus- pension is harder). Direction “b” Rebound damping is decreased (sus- pension is softer). Rebound damping Minimum (soft) 20 click(s) in direction “b”* Standard 7. Clean: 12 click(s) in direction “b”* • Dust seal “a” Maximum (hard) •...

  • Page 64: Checking The Rear Shock Absorber Assembly

    CHASSIS Direction “a” Bleed screw (front fork) Compression damping is increased 1.3 N·m (0.13 kgf·m, 0.95 lb·ft) (suspension is harder). Direction “b” Compression damping is decreased (suspension is softer). Compression damping Minimum (soft) 20 click(s) in direction “b”* Standard 12 click(s) in direction “b”* Maximum (hard) 0 click(s) in direction “b”* * With the adjusting screw fully turned in di-...
  • Page 65 CHASSIS 1. Remove: • Rear frame 2. Adjust: • Spring preload a. Loosen the locknut “1”. b. Loosen the adjuster “2” until there is some clearance between the spring and the ad- juster. c. Measure the spring free length “a”. e.
  • Page 66 CHASSIS Compression damping (for fast compres- Compression damping (for slow compres- sion damping) sion damping) ECA24370 ECA24390 NOTICE NOTICE Do not turn the adjuster forcibly beyond its Do not turn the adjuster forcibly beyond its adjusting range. adjusting range. 1. Adjust: 1.

  • Page 67: Checking The Swingarm Operation

    CHASSIS a. Bead stopper tightening nut EAM30240 CHECKING THE SWINGARM OPERATION b. Tire valve stem 1. Check: • Swingarm smooth action EAM30244 CHECKING AND TIGHTENING THE SPOKES • Swingarm free play 1. Check: Refer to “SWINGARM” on page 4-28. • Spoke Bend/damage ...

  • Page 68: Checking The Wheels

    CHASSIS able lubricating device. Nipple (spoke) 2.5 N·m (0.25 kgf·m, 1.8 lb·ft) EAM30483 LUBRICATING THE BRAKE LEVER 1. Lubricate the pivoting points and metal-to- • Do not give a half turn (180) or more for one metal moving parts of the following parts. tightening.
  • Page 69 CHASSIS GENERAL CHASSIS..................4-1 REMOVING THE NUMBER PLATE ............4-1 REMOVING THE SIDE COVER ..............4-1 FRONT WHEEL ....................4-2 REMOVING THE FRONT WHEEL .............4-2 INSTALLING THE FRONT WHEEL ............4-2 REAR WHEEL ....................4-3 REMOVING THE REAR WHEEL ...............4-3 CHECKING AND REPLACING THE REAR WHEEL SPROCKET.....4-3 INSTALLING THE REAR WHEEL ..............4-3 FRONT BRAKE ....................4-5 REPLACING THE FRONT BRAKE PADS ..........4-5...
  • Page 70 CHAIN DRIVE ....................4-29 REMOVING THE DRIVE CHAIN ..............4-29 CHECKING THE DRIVE CHAIN ..............4-29 CHECKING THE DRIVE SPROCKET ............4-30 CHECKING THE REAR WHEEL SPROCKET .........4-30 INSTALLING THE DRIVE CHAIN ............4-30...

  • Page 71: General Chassis

    GENERAL CHASSIS EAM20094 GENERAL CHASSIS EAM30371 REMOVING THE NUMBER PLATE 1. Remove: • Number plate bolt • Number plate “1” • The projection “a” is inserted into the band of the number plate. Pull the band off the projec- tion before removal. •...

  • Page 72: Front Wheel

    FRONT WHEEL EAM20095 ECA24430 FRONT WHEEL NOTICE Before tightening the front wheel axle nut, EAM30017 push down hard on the handlebar(s) several REMOVING THE FRONT WHEEL times and check if the front fork rebounds 1. Use a maintenance stand to raise the front smoothly.

  • Page 73: Rear Wheel

    REAR WHEEL EAM20096 REAR WHEEL EAM30022 REMOVING THE REAR WHEEL 1. Use a maintenance stand to raise the rear wheel off the ground. EWA13120 WARNING Securely support the vehicle so that there is no danger of it falling over. G088904 b.
  • Page 74 REAR WHEEL Refer to “DRIVE CHAIN SLACK” on page 3-16. 3. Install: • Left drive chain puller “1” 6. Tighten: • Rear wheel axle “2” • Rear wheel axle nut “1” • Install the left drive chain puller, and insert the Rear wheel axle nut rear wheel axle from the left side.

  • Page 75: Front Brake

    FRONT BRAKE EAM20097 FRONT BRAKE Brake pad lining thickness limit 1.0 mm (0.04 in) EAM30519 REPLACING THE FRONT BRAKE PADS When replacing the brake pads, it is not neces- sary to disconnect the brake hose or disassem- ble the brake caliper. 1.
  • Page 76 FRONT BRAKE e. Install the brake caliper “4” and tighten the pad pin “5”. Front brake caliper bolt 28 N·m (2.8 kgf·m, 21 lb·ft) Brake pad pin 17 N·m (1.7 kgf·m, 13 lb·ft) f. Install the pad pin plug “6”. Brake pad pin plug 2.5 N·m (0.25 kgf·m, 1.8 lb·ft) 4.

  • Page 77: Rear Brake

    REAR BRAKE pads as a set. EAM20098 REAR BRAKE Brake pad lining thickness limit 1.0 mm (0.04 in) EAM30523 REPLACING THE REAR BRAKE PADS When replacing the brake pads, it is not neces- sary to disconnect the brake hose or disassem- ble the brake caliper.
  • Page 78 REAR BRAKE Refer to “BLEEDING THE HYDRAULIC BRAKE SYSTEM” on page 3-15. e. Install the brake caliper “5” and the rear wheel “6”. f. Tighten the pad pin “7”. Brake pad pin 17 N·m (1.7 kgf·m, 13 lb·ft) g. Install the pad pin plug “8” and the protector “9”.

  • Page 79: Handlebar

    HANDLEBAR EAM20099 EAM30054 HANDLEBAR INSTALLING THE HANDLEBAR 1. Stand the vehicle upright on a level surface. EAM30052 EWA13120 REMOVING THE HANDLEBAR WARNING 1. Stand the vehicle upright on a level surface. Securely support the vehicle so that there is EWA13120 no danger of it falling over.
  • Page 80 HANDLEBAR stalled with the punch marks “a” facing for- 4. Tighten: • Lower handlebar holder nut “1” ward. • Install the handlebar so that the marks “b” are Lower handlebar holder nut in place on both sides. 40 N·m (4.0 kgf·m, 30 lb·ft) •...
  • Page 81 HANDLEBAR clamp should be installed according to the di- the slot “c” in the tube guide. mensions shown. • Pass the engine stop switch lead in the middle of the clutch lever holder. 0 mm (0 in) 0 mm (0 in) 10.Install: •...
  • Page 82 HANDLEBAR Throttle cable cap screw 0.5 N·m (0.05 kgf·m, 0.37 lb·ft) 12.Install: • Throttle cable “1” (to tube guide “2”) 15.Adjust: Apply the lithium soap base grease on the throt- • Throttle grip free play tle cable end and tube guide cable winding por- Refer to “CHECKING THE THROTTLE tion.
  • Page 83 HANDLEBAR 18.Install: • Grip cap bolt “1” Grip cap bolt 3.8 N·m (0.38 kgf·m, 2.8 lb·ft) EWA21080 WARNING After tightening the bolts, check that the throttle grip “2” moves smoothly. If it does not, retighten the bolts for adjustment. 4-13...

  • Page 84: Front Fork

    FRONT FORK EAM20100 FRONT FORK • While compressing the inner tube “2”, set the cap bolt ring wrench “4” between the inner tube EAM30055 and locknut “3”. REMOVING THE FRONT FORK LEGS • Hold the locknut and remove the adjuster. 1.

  • Page 85: Checking The Front Fork Legs

    FRONT FORK dial gauge reading. EWA13650 WARNING Do not attempt to straighten a bent inner tube as this may dangerously weaken it. 2. Check: • Outer tube Scratches/wear/damage  Replace. 3. Measure: • Fork spring free length “a” 5. Remove: Out of specification ...

  • Page 86: Assembling The Front Fork Legs

    1. Stretch the damper assembly fully. 2. Fill: • Damper assembly Recommended oil Yamaha Suspension Oil S1 Standard oil amount 205 cm³ (6.93 US oz, 7.21 Imp.oz) 6. Check: • Upper spring seat “1”...
  • Page 87 FRONT FORK Standard oil level 145–148 mm (5.71–5.83 in) From top of fully stretched damper assembly. 7. Install: • Base valve “1” (to the damper assembly “2”) First bring the damper rod pressure to a maxi- mum. Then install the base valve while releasing the damper rod pressure.
  • Page 88 FRONT FORK 10.After filling, pump the damper assembly “1” 13.Check: slowly up and down more than 10 times to • Damper assembly smooth movement Tightness/binding/rough spots  Repeat the distribute the fork oil. steps (1) to (12). 11.While protecting the damper assembly “1” with a cloth and compressing fully, allow ex- 14.Install: •...
  • Page 89 FRONT FORK G088922 G088923 15.Install: 18.Install: • Piston metal “1” • Oil seal “1” Install the piston metal onto the slot on inner Using a fork seal driver “2”, press the oil seal in until the stopper ring groove fully appears. tube.
  • Page 90 FRONT FORK 21.Check: 24.Install: • Inner tube smooth movement • Damper assembly “1” Tightness/binding/rough spots  Repeat the (to the inner tube “2”) steps (14) to (20). ECA24560 NOTICE Allow the damper assembly to slide slowly down the inner tube until it contacts the bot- tom of the inner tube.
  • Page 91 30.Fill: • Front fork leg Recommended oil If it is installed with a gap out of specification, Yamaha Suspension Oil S1 correct damping force cannot be obtained. Standard oil amount 315 cm³ (10.7 US oz, 11.1 Imp.oz) Extent of adjustment 300–365 cm³...

  • Page 92: Installing The Front Fork Legs

    FRONT FORK 31.Install: 2. Tighten: • Damper assembly “1” • Damper assembly “1” (to the outer tube) Damper assembly (front fork) 30 N·m (3.0 kgf·m, 22 lb·ft) Temporarily tighten the damper assembly. Use the cap bolt ring wrench “2” to tighten the damper assembly.
  • Page 93 FRONT FORK Upper bracket pinch bolt 21 N·m (2.1 kgf·m, 15 lb·ft) • Lower bracket pinch bolt “2” Lower bracket pinch bolt 21 N·m (2.1 kgf·m, 15 lb·ft) EWA19320 WARNING Tighten the lower bracket to specified 7. Adjust: torque. If torqued too much, it may cause the •...

  • Page 94: Steering Head

    STEERING HEAD c. Install a new bearing race. EAM20101 STEERING HEAD ECA14270 NOTICE EAM30060 If the bearing race is not installed properly, REMOVING THE LOWER BRACKET the steering head pipe could be damaged. 1. Use a maintenance stand to raise the front wheel off the ground.
  • Page 95 STEERING HEAD 2. Install: • Bearing race • Upper bearing “1” • Bearing race cover “2” Apply the lithium-soap-based grease on the bearing and bearing race cover lip. 5. Check the steering stem by turning this lock to lock. If there is any binding, remove the steering stem and check the steering bear- ing.
  • Page 96 STEERING HEAD Upper bracket pinch bolt 21 N·m (2.1 kgf·m, 15 lb·ft) • Lower bracket pinch bolt “2” Lower bracket pinch bolt 21 N·m (2.1 kgf·m, 15 lb·ft) EWA19330 WARNING Tighten the lower bracket to specified 8. Install: torque. If torqued too much, it may cause the •...

  • Page 97: Rear Shock Absorber Assembly

    REAR SHOCK ABSORBER ASSEMBLY EAM20102 REAR SHOCK ABSORBER AS- SEMBLY EAM30065 REMOVING THE REAR SHOCK ABSORBER ASSEMBLY 1. Use a maintenance stand to raise the rear wheel off the ground. EWA13120 WARNING Securely support the vehicle so that there is no danger of it falling over.

  • Page 98: Swingarm

    SWINGARM EAM20103 SWINGARM EAM30071 REMOVING THE SWINGARM 1. Use a maintenance stand to raise the rear wheel off the ground. EWA13120 WARNING Securely support the vehicle so that there is no danger of it falling over. 2. Measure: • Swingarm side play •...

  • Page 99: Chain Drive

    CHAIN DRIVE Drive chain 15-link section length “c” = EAM20104 CHAIN DRIVE (length “a” between pin inner sides + length “b” between pin outer sides)/2 EAM30075 REMOVING THE DRIVE CHAIN 1. Use a maintenance stand to raise the rear wheel off the ground. EWA13120 WARNING Securely support the vehicle so that there is...

  • Page 100: Checking The Drive Sprocket

    CHAIN DRIVE Damage/wear  Replace the drive chain. face in the direction of drive chain rotation. • Never install a new drive chain onto worn drive chain sprockets; this will dramatically shorten the drive chain’s life. G088942 5. Lubricate: • Drive chain G089069 Recommended lubricant Chain lubricant suitable for O-...
  • Page 101 CHAIN DRIVE the drive chain slack within the specified lim- its. 4-31...
  • Page 102 CHAIN DRIVE 4-32...

  • Page 103: Engine

    ENGINE CLUTCH......................5-1 REMOVING THE CLUTCH ................5-1 CHECKING THE FRICTION PLATES ............5-1 CHECKING THE CLUTCH PLATES ............5-1 CHECKING THE CLUTCH SPRINGS ............5-1 CHECKING THE CLUTCH HOUSING ............5-1 CHECKING THE CLUTCH BOSS ..............5-2 CHECKING THE PRESSURE PLATE ............5-2 CHECKING THE PUSH LEVER SHAFT ............5-2 CHECKING THE PUSH RODS ..............5-2 CHECKING THE PRIMARY DRIVE GEAR ..........5-2 CHECKING THE PRIMARY DRIVEN GEAR..........5-2...
  • Page 104 CLUTCH 2. Measure: EAM20111 CLUTCH • Clutch plate warpage (with a surface plate and thickness gauge) EAM30108 Out of specification  Replace the clutch REMOVING THE CLUTCH plates as a set. 1. Remove: • Clutch boss nut “1” Thickness gauge •...
  • Page 105 CLUTCH EAM30113 CHECKING THE CLUTCH BOSS 1. Check: • Clutch boss splines Damage/pitting/wear  Replace the clutch boss. Pitting on the clutch boss splines will cause er- ratic clutch operation. 2. Measure: • Push rod 2 bending limit Out of specification  Replace. Push rod bending limit 0.30 mm (0.012 in) EAM30117...
  • Page 106 CLUTCH Universal clutch holder 90890-04086 Universal clutch holder YM-91042 2. Install: • Thrust washer [D = ø34 mm (1.34 in)] “1” • Spacer “2” • Bearing “3” • Primary driven gear “4” 5. Bend the lock washer “1” tab. Apply the transmission oil on the bearing, spacer and primary driven gear inner circumference.
  • Page 107 CLUTCH tern. Apply the transmission oil on the bearing, wash- 11.Install: er and push rod 1. • Dowel pin “1” • Gasket (clutch cover) “2” 8. Install: • Push rod 2 “1” 12.Install: • Ball “2” • Clutch cover • Push rod 1 “3” •...
  • Page 108 CLUTCH...

  • Page 109: Electrical System

    ELECTRICAL SYSTEM WIRING DIAGRAM ...................6-1 COLOR CODE....................6-1...
  • Page 110 WIRING DIAGRAM EAM20195 WIRING DIAGRAM 1. Engine stop switch 2. CDI unit 3. Ignition coil 4. CDI magneto 5. Spark plug EAM30608 COLOR CODE Black Orange Yellow Black/Red Black/White Green/Blue Green/White White/Blue White/Red...

  • Page 111: Troubleshooting

    TROUBLESHOOTING TROUBLESHOOTING ..................7-1 GENERAL INFORMATION ................7-1 TROUBLESHOOTING OF ENGINE ............7-1 TROUBLESHOOTING OF CLUTCH ............7-6 TROUBLESHOOTING OF TRANSMISSION ..........7-7 TROUBLESHOOTING OF COOLING SYSTEM ........7-8 TROUBLESHOOTING OF BRAKE ............7-9 TROUBLESHOOTING OF SUSPENSION ..........7-9 TROUBLESHOOTING OF STEERING/HANDLING.........7-11...

  • Page 112: Troubleshooting

    • The following guide for troubleshooting represent quick and easy procedures for checking these vital systems yourself. However, should your motorcycle require any repair, take it to a Yamaha dealer, whose skilled technicians have the necessary tools, experience, and know-how to service the motor- cycle properly.
  • Page 113 TROUBLESHOOTING Symptom Possible cause Actions Measure the compression pres- — sure. Tighten the spark plugs to the Loose spark plug specified torque. Tighten bolts or nuts on cylinder Loose cylinder head or cylinder head and cylinder to the specified torque. Compression pressure is low Damaged cylinder head gasket Replace the cylinder head gasket.
  • Page 114 TROUBLESHOOTING Symptom Possible cause Actions Damaged or worn needle valve Replace the needle valve. Adjust the fuel level to the proper Incorrect fuel level level. Bent, worn, or damaged starter Replace the starter plunger. plunger Incorrectly adjusted starter cable Adjust the starter cable. Clogged or damaged carburetor Clean, repair, or replace the car- breather hose...
  • Page 115 TROUBLESHOOTING Symptom Possible cause Actions Water or foreign material in fuel, Change fuel. degraded fuel Clogged carburetor air passage Clean the carburetor. Incorrectly adjusted throttle cable Adjust the throttle grip free play. Improperly synchronized carbure- Adjust synchronization of carbure- tors tors.
  • Page 116 TROUBLESHOOTING Symptom Possible cause Actions Check the air induction system. Failed air induction system Repair or replace faulty parts. Clogged vacuum hose Clean the vacuum hose. Cracks and damage in vacuum Replace the vacuum hose. hose — Damaged carburetor joint Replace the carburetor joint.

  • Page 117: Troubleshooting Of Clutch

    TROUBLESHOOTING EAM30510 TROUBLESHOOTING OF CLUTCH Manual clutch Symptom Possible cause Actions Improperly assembled clutch Reassemble the clutch. Improperly adjusted clutch cable Adjust the clutch lever free play. Tighten the clutch spring bolts to Loose clutch spring the specified torque. Replace the clutch springs as a Fatigued clutch spring set.

  • Page 118: Troubleshooting Of Transmission

    TROUBLESHOOTING Symptom Possible cause Actions Replace the primary drive gear or Damaged or worn primary driven crankshaft, and the clutch housing gear as a set. Tighten the clutch boss nut to the Loose clutch boss nut specified torque. Clutch noise Fatigued clutch damper Replace the clutch housing.

  • Page 119: Troubleshooting Of Cooling System

    TROUBLESHOOTING EAM30512 TROUBLESHOOTING OF COOLING SYSTEM Symptom Possible cause Actions Carbon buildup in piston head and Clean the piston head and com- combustion chamber bustion chamber. Clogged engine cooling water Check and clean the engine cool- passages ing water passages. Damaged or leaking radiator Replace the radiator.

  • Page 120: Troubleshooting Of Brake

    TROUBLESHOOTING EAM30513 TROUBLESHOOTING OF BRAKE Symptom Possible cause Actions Worn brake pad Replace the brake pads as a set. Worn or deflected brake disc Replace the brake disc. Air in hydraulic brake system Bleed the hydraulic brake system. Check the hydraulic brake system Brake fluid leakage and repair or replace faulty parts as necessary.
  • Page 121 TROUBLESHOOTING Symptom Possible cause Actions Fatigued or broken fork spring Replace the fork spring. Incorrect oil viscosity (low) Change to recommended fork oil. Incorrect oil level (low) Adjust to the specified oil level. Improperly adjusted spring pre- Adjust the spring preload. Front fork is soft load (soft) Improperly adjusted rebound...

  • Page 122: Troubleshooting Of Steering/Handling

    TROUBLESHOOTING Symptom Possible cause Actions Oil leaking from rear shock Replace the rear shock absorber. absorber Gas leaking from rear shock Replace the rear shock absorber. absorber Fatigued or damaged rear shock Replace the rear shock absorber. absorber spring Rear suspension is soft Improperly adjusted rear shock Adjust the spring preload.
  • Page 123 TROUBLESHOOTING Symptom Possible cause Actions Tighten the spoke and adjust the Loose spoke runout. Damaged or worn wheel bearing Replace the wheel bearing. Worn, deformed, or incorrect tire Replace the tire. Tighten the wheel axle nut to the Loose wheel axle nut Rear wheel vibration specified torque.
  • Page 124 TROUBLESHOOTING 7-13...

  • Page 125: Tuning

    TUNING ENGINE......................8-1 CARBURETOR SETTING ................8-1 ATMOSPHERIC CONDITIONS AND CARBURETOR SETTINGS ....8-1 TEST RUN ....................8-1 EFFECTS OF THE SETTING PARTS ON THE THROTTLE VALVE OPENING ....................8-2 MAIN JET ADJUSTMENT ................8-2 PILOT AIR SCREW ADJUSTMENT ............8-2 PILOT JET ADJUSTMENT .................8-2 JET NEEDLE ADJUSTMENT ..............8-3 JET NEEDLE GROOVE POSITION ADJUSTMENT ........8-3 RELATIONSHIP WITH THROTTLE OPENING..........8-3 CARBURETOR SETTING PARTS .............8-4...

  • Page 126: Engine

    ENGINE in the air by so much of the water vapor in the EAM20198 ENGINE same air. • Lower atmospheric pressure (at a high alti- EAM30590 tude) reduces the density of the air. CARBURETOR SETTING • The role of fuel is to cool the engine, and in the EAM30592 case of a 2-stroke engine, to lubricate the en- TEST RUN...

  • Page 127: Effects Of The Setting Parts On The Throttle Valve Opening

    ENGINE EAM30593 EFFECTS OF THE SETTING PARTS ON THE THROTTLE VALVE OPENING EAM30595 PILOT AIR SCREW ADJUSTMENT The richness of the air-fuel mixture with the throttle fully closed to 1/4 open can be set by turning the pilot air screw “1”. Turning in the pilot air screw will make the mix- ture enrich at low speeds, and turning it out will lean it.

  • Page 128: Jet Needle Adjustment

    JET NEEDLE ADJUSTMENT Whether or not the richness of the mixture is On the carburetors used in the YZ125 the main proper is hard to be determined by means of the nozzle is a non disassembly type, so it can not spark plug and therefore, it should be judged be replaced.

  • Page 129: Carburetor Setting Parts

    ENGINE Part name Size Part number Pilot jet Rich 4KM-14142-50 #47.5 4KM-14142-47 4KM-14142-45 #42.5 4KM-14142-42 (STD) 4KM-14142-40 #37.5 4KM-14142-37 Example: 4KM-14142-35 #32.5 4KM-14142-32 6BFY43-74-3 Lean 4KM-14142-30 6BFY43-74-2 Throttle Rich 6BFY43-75-3 valve (STD) 1C3-14112-40 A. Lean (larger diameter) Lean 4.25 1C3-14112-42 B.

  • Page 130: Road Condition And Examples Of Carburetor Setting

    ENGINE EAM30601 ROAD CONDITION AND EXAMPLES OF CARBURETOR SETTING General condition Sandy condition 15–25 C 15–25 C Under 10 C Over 30 C Under 10 C Over 30 C (59–77 F) (59–77 F) (50 F) (86 F) (50 F) (86 F) (Spring, (Spring, (Winter)
  • Page 131 ENGINE Symptom Setting Checking Lean mixture Lower jet needle clip position. (1 groove down) Rich mixture Raise jet needle clip position. (1 groove up) • 1/4–3/4 throttle Lower jet needle clip position. (1 Leaner *Hard breathing groove down) Lack of speed (Standard) 1.

  • Page 132: Change Of The Heat Range Of Spark Plugs

    ENGINE EAM30603 CHANGE OF THE HEAT RANGE OF SPARK PLUGS Judging from the discoloration of spark plugs, if they are found improper, it can be corrected by the following two methods; changing carburetor settings and changing the heat range of spark plug.

  • Page 133: Chassis

    CHASSIS EAM20119 Part name Type Part number CHASSIS Rear wheel 17D-25447-50 EAM30168 sprocket “2” SELECTION OF THE SECONDARY (STD) 17D-25448-50 REDUCTION RATIO (SPROCKET) 17D-25449-50 Secondary reduction ratio = Number of 17D-25450-50 rear wheel sprocket teeth/Number of 17D-25451-50 drive sprocket teeth 17D-25452-50 Secondary reduction ratio 3.692 (48/13)

  • Page 134: Front Fork Setting

    (in position etc.) when Recommended oil setting the front fork. Yamaha Suspension Oil S1 1. Use of soft spring Standard oil amount • Change the rebound damping force.

  • Page 135: Front Fork Setting Parts

    CHASSIS EAM30175 REAR SUSPENSION SETTING Generally a stiff spring gives a stiff riding feeling. The rear shock absorber setting should be made Rebound damping tends to become weaker, re- depending on the rider’s feeling of an actual run sulting in lack of a sense of contact with the road and the circuit conditions.

  • Page 136: Setting Of Spring After Replacement

    CHASSIS the same set length of the spring may change because of the initial fatigue, etc. of the spring. Therefore, be sure to make reevaluation. • If the standard figure cannot be achieved by adjusting the adjuster and changing the set length, replace the spring with an optional one and make readjustment.
  • Page 137 CHASSIS color and quantity of I.D. marks. • Spring preload adjusting positions Spring preload adjusting positions Minimum Position in which the spring is turned in 1.5 mm (0.06 in) from its free length. Standard Position in which the spring is turned in 8.0 mm (0.31 in) from its free length.

  • Page 138: Suspension Setting (Front Fork)

    CHASSIS EAM30179 SUSPENSION SETTING (FRONT FORK) • If any of the following symptoms is experienced with the standard position as the base, make resetting by reference to the adjustment procedure given in the same chart. • Before any change, set the rear shock absorber sunken length to the standard figure 90–100 mm (3.5–3.9 in).

  • Page 139: Suspension Setting (Rear Shock Absorber)

    CHASSIS Section Symptom Check Adjust Large Medium Small Jump Compression Turn adjuster clockwise (about 2 damping force clicks) to increase damping. Turn adjuster counterclockwise Rebound damp- (about 2 clicks) to decrease ing force damping. Low front, tend-   ing to lower front Set sunken length for 95–100 posture Balance with rear...
  • Page 140 CHASSIS Section Symptom Check Adjust Large Medium Small Jump Turn adjuster counterclockwise Rebound damp- (about 2 clicks) to decrease Heavy and drag- ing force   damping. ging Spring Replace with soft spring. Turn adjuster counterclockwise Rebound damp- (about 2 clicks) to decrease ing force damping.
  • Page 141 EAM20160 Genuine Yamaha Parts text 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 –...
  • Page 142 PRINTED IN JAPAN 2020.05-0.4×1 !

Table of Contents