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Yamaha YFB250(D) 1992 Service Manual

This Yamaha YFB250(D) Service Manual was written by the Yamaha Motor Company, Ltd. primarily for use by Yamaha dealers and qualified mechanics. It is not possible to put an entire mechanic’s education into one manual, so persons using this book to perform maintenance and repairs on Yamaha machines should have a basic understanding of the machanical concepts and procedures inherent in machine repair technology. Without such knowledge, attempted repairs or service to the machine may render it unfit to use and/or unsafe. Yamaha Motor Company, Ltd. is continually striving to improve all models manufactured by Yamaha. Modifications and significant changes in specifications or procedures will be forwarded to all Authorized Yamaha dealers and will, where applicable, appear in future editions of this manual.

Table of contents

CHAPTER 1.
GENERAL INFORMATION

MACHINE IDENTIFICATION 1-1
VEHICLE IDENTIFICATION NUMBER (FOR USA, CDN AND AUS) 1-1
FRAME SERIAL NUMBER (EXCEPT FOR USA, CDN AND AUS) 1-1
ENGINE SERIAL NUMBER 1-1

IMPORTANT INFORMATION 1-2
PREPARATION FOR REMOVAL AND DISASSEMBLY 1-2
ALL REPLACEMENT PARTS 1-2
GASKETS, OIL SEALS, AND 0-RINGS 1-2
LOCK WASHERS/PLATES AND COTTER PINS 1-2
BEARINGS AND OIL SEALS 1-3
CIRCLIPS 1-3

SPECIAL TOOLS 1-3
FORTUNE-UP 1-3
FOR ENGINE SERVICE 1-4
FOR MIDDLE GEAR SERVICE 1-7
FOR FINAL GEAR SERVICE 1-8
FOR ELECTRICAL COMPONENTS 1-9

CHAPTER 2.

SPECIFICATIONS

GENERAL SPECIFICATIONS 2-1

MAINTENANCE SPECIFICATIONS 2-4
ENGINE 2-4
CHASSIS 2-12
ELECTRICAL 2-15

GENERAL TORQUE SPECIFICATIONS 2-17

DEFINITION OF UNITS 2-17

LUBRICATION POINTS AND LUBRICANT TYPE 2-18
ENGINE 2-18
CHASSIS 2-19

LUBRICATION DIAGRAMS 2-20

CABLE ROUTING 2-22

CHAPTER 3.

PERIODIC INSPECTION AND ADJUSTMENT

INTRODUCTION 3-1

PERIODIC MAINTENANCE/LUBRICATION 3-1

FENDERS AND FUEL TANK 3-2
FRONT FENDER 3-2
REAR FENDER 3-3
FUEL TANK 3-6

ENGINE 3-8
VALVE CLEARANCE ADJUSTMENT 3-8
TIMING CHAIN TENSIONER ADJUSTMENT 3-11
IDLE SPEED ADJUSTMENT 3-11
THROTTLE CABLE FREE PLAY ADJUSTMENT 3-12
SPEED LIMITER ADJUSTMENT 3-13
SPARK PLUG INSPECTION 3-14
IGNITION TIMING CHECK 3-15

COMPRESSION PRESSURE MEASUREMENT 3-16
ENGINE OIL LEVEL INSPECTION 3-18
ENGINE OIL REPLACEMENT 3-19
CLUTCH ADJUSTMENT 3-21
AIR FILTER CLEANING 3-22

CHASSIS 3-23
FRONT AND REAR BRAKE LINING INSPECTION 3-23
FRONT BRAKE ADJUSTMENT 3-24
REAR BRAKE LEVER AND PEDAL ADJUSTMENT 3-25
DRIVE SELECT LEVER POSITION ADJUSTMENT 3-27
FINAL DRIVE GEAR OIL LEVEL INSPECTION 3-27
FINAL DRIVE GEAR OIL REPLACEMENT 3-28
DRIVE SHAFT DUST BOOT INSPECTION 3-29
STEERING SYSTEM INSPECTION 3-29
TOE-IN ADJUSTMENT 3-30
FRONT AND REAR SHOCK ABSORBERS INSPECTION 3-32
TIRE INSPECTION 3-33
WHEEL INSPECTION 3-35

ELECTRICAL 3-35
BATTERY INSPECTION 3-35
FUSE INSPECTION 3-38
HEADLIGHT BEAM ADJUSTMENT 3-39
HEADLIGHT BULB REPLACEMENT 3-40

CHAPTER 4.

ENGINE OVERHAUL

ENGINE REMOVAL 4-1
PREPARATION FOR REMOVAL 4-1
FRONT FENDER AND REAR FENDER 4-1
ENGINE OIL 4-2
EXHAUST PIPE AND MUFFLER 4-2
CARBURETOR 4-2
STARTER MOTOR 4-3
REAR BRAKE CABLES AND FOOTREST 4-3
WIRINGS AND HOSES 4-3
REAR WHEEL DRIVE ASSEMBLY AND SWINGARM 4-4
ENGINE REMOVAL 4-4

ENGINE DISASSEMBLY 4-5
CYLINDER HEAD ASSEMBLY, CYLINDER AND PISTON 4-5
STARTER PULLEY (EXCEPT FOR USA) AND CDI MAGNETO 4-8
MIDDLE DRIVEN PINION GEAR 4-10
PRIMARY AND SECONDARY CLUTCHES 4-11
OIL PUMP AND SHIFTER 4-13
BALANCER DRIVEN GEAR 4-15
CRANKCASE (LEFT) 4-15
BALANCER SHAFT, TRANSMISSION AND CRANKSHAFT 4-16
CYLINDER HEAD 4-17
VALVE 4-18
RECOIL STARTER (EXCEPT FOR USA) 4-19

INSPECTION AND REPAIR 4-20
CYLINDER HEAD 4-20
INTAKE AND EXHAUST VALVE 4-20
VALVE GUIDE 4-21
VALVE SEAT 4-22
VALVE SPRING 4-25
VALVE INSTALLATION 4-26
CAM SHAFT 4-27
ROCKER ARM AND ROCKER ARM SHAFT 4-28
TIMING CHAIN 4-30
CAM SPROCKET AND CAM DRIVE SPROCKET 4-31
TIMING CHAIN GUIDE 4-31
TIMING CHAIN TENSIONER 4-31
TAPPET COVER AND CAM SPROCKET COVER 4-32
CYLINDER AND PISTON 4-32
PISTON RING AND PISTON PIN 4-33
CRANKSHAFT 4-36
BALANCER DRIVE GEAR AND DRIVEN GEARS 4-37
PRIMARY GEARS AND STARTER 4-37
PRIMARY CLUTCH 4-38
SECONDARY CLUTCH 4-38
OIL PUMP 4-40
TRANSMISSION AND SHIFTER 4-41
MIDDLE GEAR 4-43
BEARINGS AND OIL SEALS 4-43
CIRCLIPS AND WASHERS 4-43
CRANKCASE 4-43
RECOIL STARTER (EXCEPT FOR USA) 4-44

ENGINE ASSEMBLY AND ADJUSTMENT 4-45
RECOIL STARTER (EXCEPT FOR USA) 4-45
CRANKSHAFT, TRANSMISSION AND BALANCER SHAFT 4-50
CRANKCASE (LEFT) 4-51
BALANCER DRIVEN AND DRIVE GEARS 4-51
SHIFTER AND OIL PUMP 4-54
PRIMARY AND SECONDARY CLUTCHES 4-57
MIDDLE DRIVEN GEAR 4-61
STARTER PULLEY (EXCEPT FOR USA) AND CDI MAGNETO 4-63
CYLINDER HEAD ASSEMBLY, CYLINDER AND PISTON 4-67
REMOUNTING ENGINE 4-72

CHAPTER 5.

CARBURETION

CARBURETOR 5-1
REMOVAL 5-2
DISASSEMBLY 5-2
INSPECTION 5-3
ASSEMBLY 5-5
INSTALLATION 5-6
FUEL LEVEL ADJUSTMENT 5-7

 

CHAPTER 6.

DRIVE TRAIN

MIDDLE GEAR SERVICE 6-1
MIDDLE GEAR SHIMS 6-2
REMOVAL 6-3
DISASSEMBLY 6-5
INSPECTION 6-7
MIDDLE GEAR SHIM SELECTION 6-9
ASSEMBLY 6-16
MIDDLE GEAR LASH ADJUSTMENT 6-21
INSTALLATION 6-22

FINAL DRIVE GEAR AND DRIVE SHAFT 6-24
TROUBLESHOOTING 6-25
REMOVAL 6-28
DISASSEMBLY 6-29
INSPECTION 6-31
FINAL DRIVE PINION GEAR AND RING GEAR SHIM SELECTION 6-32
ASSEMBLY 6-35
FINAL GEAR GEAR LASH MEASUREMENT AND ADJUSTMENT 6-37
INSTALLATION 6-40

CHAPTER 7.

CHASSIS

FRONT WHEELS AND FRONT BRAKE 7-1
REMOVAL 7-2
INSPECTION 7-3
INSTALLATION 7-6

REAR WHEELS/REAR BRAKE AND REAR AXLE 7-9
REMOVAL 7-11
INSPECTION 7-13
INSTALLATION 7-16

STEERING SYSTEM 7-21
REMOVAL 7-22
INSPECTION 7-24
INSTALLATION 7-25

FRONT SHOCK ABSORBER AND LOWER ARM 7-29
REMOVAL 7-30
INSPECTION 7-32
INSTALLATION 7-33

REAR SHOCK ABSORBER AND SWINGARM 7-36
REMOVAL 7-37
INSPECTION 7-39
INSTALLATION . 7-40

CHAPTER 8.

ELECTRICAL

YFB250 (D) ’92 CIRCUIT DIAGRAM 8-1

ELECTRICAL COMPONENTS 8-3

CHECKING OF SWITCHES 8-4
SWITCH CONNECTION AS SHOWN IN MANUAL 8-4
CHECKING SWITCH FOR TERMINAL CONNECTION 8-4
CHECKING OF BULBS 8-7
KINDS OF BULBS 8-7
CHECKING BULBS CONDITION 8-7

IGIMITION SYSTEM 8-9
CIRCUIT DIAGRAM 8-9
TROUBLESHOOTING 8-10

ELECTRIC STARTING SYSTEM 8-14
CIRCUIT DIAGRAM B-U
STARTING CIRCUIT OPERATION 8-15
TROUBLESHOOTING 8-16
STARTER MOTOR TEST 8-21

CHARGING SYSTEM 8-26
CIRCUIT DIAGRAM 8-26
TROUBLESHOOTING 8-27

LIGHTING SYSTEM 8-29
CIRCUIT DIAGRAM 8-29
TROUBLESHOOTING 8-30

SIGNAL SYSTEM 8-32
CIRCUIT DIAGRAM 8-32
TROUBLESHOOTING 8-33
SIGNAL SYSTEM TEST AND CHECK 8-35

CHAPTER 9.

TROUBLESHOOTING

STARTING FAILURE/HARD STARTING 9-1
FUEL SYSTEM 9-1
ELECTRICAL SYSTEM 9-1
COMPRESSION SYSTEM 9-2

POOR IDLE SPEED PERFORMANCE 9-2
POOR IDLE SPEED PERFORMANCE 9-2

POOR MEDIUM AND HIGH SPEED PERFORMANCE 9-2
POOR MEDIUM AND HIGH SPEED PERFORMANCE 9-2

FAULTY DRIVE TRAIN 9-3

FAULTY GEAR SHIFTING 9-4
HARD SHIFTING 9-4
SHIFT PEDAL DOES NOT MOVE 9-4
JUMP-OUT GEAR 9-4

CLUTCH SLIPPING 9-4
CLUTCH SLIPPING 9-4

CLUTCH DRAGGING 9-5
CLUTCH DRAGGING 9-5

OVERHEATING 9-5
OVERHEATING 9-5

FAULTY BRAKE 9-5
POOR BRAKING EFFECT 9-5

SHOCK ABSORBER MALFUNCTION 9-5
MALFUNCTION 9-5

INSTABLE HANDLING 9-6
INSTABLE HANDLING 9-6

FAULTY LIGHTING SYSTEM 9-6
HEADLIGHT DARK 9-6
BULB BURNT OUT 9-6

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