engine YAMAHA YBR125 2003 Owner's Guide

!$ Oil pressure1. Remove the check bolt 
 in the cylinder head.
2. Start the engine and keep it idling until oil flows out
of the bleed hole. If no oil comes out after one
minute, turn off the engine immediately so it will
not seize. In such a case go to the nearest Yamaha
dealer or other qualified mechanic for repairs.
3. After checking, tighten the check bolt to the
specified torque.
Check bolt torque:
7 N.m (0.7 Kgf.m, 5.0 lbf.ft)
1. Check bolt
1
!$ Oil pressure1. Remove the check bolt 
 in the cylinder head.
2. Start the engine and keep it idling until oil flows out
of the bleed hole. If no oil comes out after one
minute, turn off the engine immediately so it will
not seize. In such a case go to the nearest Yamaha
dealer or other qualified mechanic for repairs.
3. After checking, tighten the check bolt to the
specified torque.
Check bolt torque:
7 N.m (0.7 Kgf.m, 5.0 lbf.ft)
1. Check bolt
1

5. Remove the air filter elements from the guide and clean
them with solvent. After cleaning, remove the remaining
solvent by squeezing the air filter.
6. Apply recommended oil to the entire surface of the filter
and squeeze out the excess oil. The air filter should be
wet but not dripping.
Recommended oil:
Engine oil 20W50
7. Reinstall the air filter and lock it with the clamp.
8. Install the air filter case cover and the right side cover.
Make sure the element is properly seated in the air filter
case.
The engine should never be run without the air filter
element installed; excessive piston and/or cylinder wear
may result.
!
CAUTION:
CAUTION:
5. Remove the air filter elements from the guide and clean
them with solvent. After cleaning, remove the remaining
solvent by squeezing the air filter.
6. Apply recommended oil to the entire surface of the filter
and squeeze out the excess oil. The air filter should be
wet but not dripping.
Recommended oil:
Engine oil 20W50
7. Reinstall the air filter and lock it with the clamp.
8. Install the air filter case cover and the right side cover.
Make sure the element is properly seated in the air filter
case.
The engine should never be run without the air filter
element installed; excessive piston and/or cylinder wear
may result.
!
CAUTION:
CAUTION:

Valve clearance adjustment
The correct valve clearance changes with use, resulting in
improper fuel/air supply or engine noise. To prevent this,
valve clearance must be adjusted regularly. This adjustment,
however, should be left to a professional Yamaha service
technician.
Carburetor adjustment
The carburetor is a vital part of the engine. Adjusting should
be left to a Yamaha dealer who has the professional
knowledge, specialized data, and equipment to do so
properly. However, the following may be serviced by the
owner as part of routine maintenance.
The carburetor was set at Yamaha factory after many
tests. If the settings are changed, poor engine
performance and damage may result.
!
CAUTION:
Valve clearance adjustment
The correct valve clearance changes with use, resulting in
improper fuel/air supply or engine noise. To prevent this,
valve clearance must be adjusted regularly. This adjustment,
however, should be left to a professional Yamaha service
technician.
Carburetor adjustment
The carburetor is a vital part of the engine. Adjusting should
be left to a Yamaha dealer who has the professional
knowledge, specialized data, and equipment to do so
properly. However, the following may be serviced by the
owner as part of routine maintenance.
The carburetor was set at Yamaha factory after many
tests. If the settings are changed, poor engine
performance and damage may result.
!
CAUTION:

NOTE:
A diagnostic tachometer must be used for this procedure.
1. Attach the tachometer. Start the engine and warm it up
for a few minutes (normally, 1 or 2 minutes) at
approximately 1,000 to 2,000 r/min. Occasionally rev
the engine to 4,000 to 5,000 r/min. The engine is warm
when it quickly responds to the throttle.
2. Set the idle to the specified engine speed by adjusting
the throttle stop screw; turn the screw in to increase
engine speed and out to decrease engine speed.
NOTE:
If the specified idle speed cannot be obtained by performing
the above adjustment, consult a Yamaha dealer.
!

Standard idle speed:
1,300 ~ 1,400 r/min
1. Throttle stop screw
Idle speed adjustment
1
NOTE:
A diagnostic tachometer must be used for this procedure.
1. Attach the tachometer. Start the engine and warm it up
for a few minutes (normally, 1 or 2 minutes) at
approximately 1,000 to 2,000 r/min. Occasionally rev
the engine to 4,000 to 5,000 r/min. The engine is warm
when it quickly responds to the throttle.
2. Set the idle to the specified engine speed by adjusting
the throttle stop screw; turn the screw in to increase
engine speed and out to decrease engine speed.
NOTE:
If the specified idle speed cannot be obtained by performing
the above adjustment, consult a Yamaha dealer.
!

Standard idle speed:
1,300 ~ 1,400 r/min
1. Throttle stop screw
Idle speed adjustment
1

NOTE:
Before checking the throttle cable free play, the engine
idling speed should be adjusted.
The throttle cable should have an specified free play in the
turning direction at the grip flange. If the free play is incorrect,
follow the instructions below.
1. Loosen the locknut.
2. Turning the adjuster to:
Direction A : increase free play
Direction B: reduces free play
3. Tighten the locknut.
!
Free play: 3 ~ 7 mm (0.12 ~ 0.28 in)
Throttle cable adjustment
1. Free play
2. Locknut
3. Adjuster
NOTE:
Before checking the throttle cable free play, the engine
idling speed should be adjusted.
The throttle cable should have an specified free play in the
turning direction at the grip flange. If the free play is incorrect,
follow the instructions below.
1. Loosen the locknut.
2. Turning the adjuster to:
Direction A : increase free play
Direction B: reduces free play
3. Tighten the locknut.
!
Free play: 3 ~ 7 mm (0.12 ~ 0.28 in)
Throttle cable adjustment
1. Free play
2. Locknut
3. Adjuster

!
1. Spark plug gap
Spark plug inspection
The spark plug is an important engine component and is
easy to inspect. The condition of the spark plug can indicate
the condition of the engine.
The ideal color on the white porcelain insulator around the
center electrode is a medium to light tan color for a
motorcycle that is being ridden normally. Do not attempt to
diagnose any problems yourself. Instead, take the
motorcycle to a Yamaha dealer. You should periodically
remove and inspect the spark plug because heat and
deposits will cause the spark plug to slowly break down
and erode.
If electrode erosion becomes excessive, or if carbon and
other deposits are excessive, you should replace the spark
plug with the specified plug.Standard spark plug:
CR7HSA (NGK) and U22FSR-U (DENSO)
Before installing the spark plug, measure the electrode gap
with a wire thickness gauge and adjust the gap to
specification as necessary.
Spark plug gap:
0.7 mm ( 0.028 in)
When installing the plug, always clean the gasket surface
and use a new gasket. Wipe off any grime from the threads,
and torque the spark plug properly.
Spark plug torque:
12.5 N.m (1.25 Kgf.m, 9 lbf.ft)
NOTE:
If a torque wrench is not available when you are installing a
spark plug, a good estimate of the correct torque is 1/4 to
1/2 turn past finger tight. Have the spark plug torqued to
the correct value as soon as possible with a torque wrench.
!
1. Spark plug gap
Spark plug inspection
The spark plug is an important engine component and is
easy to inspect. The condition of the spark plug can indicate
the condition of the engine.
The ideal color on the white porcelain insulator around the
center electrode is a medium to light tan color for a
motorcycle that is being ridden normally. Do not attempt to
diagnose any problems yourself. Instead, take the
motorcycle to a Yamaha dealer. You should periodically
remove and inspect the spark plug because heat and
deposits will cause the spark plug to slowly break down
and erode.
If electrode erosion becomes excessive, or if carbon and
other deposits are excessive, you should replace the spark
plug with the specified plug.Standard spark plug:
CR7HSA (NGK) and U22FSR-U (DENSO)
Before installing the spark plug, measure the electrode gap
with a wire thickness gauge and adjust the gap to
specification as necessary.
Spark plug gap:
0.7 mm ( 0.028 in)
When installing the plug, always clean the gasket surface
and use a new gasket. Wipe off any grime from the threads,
and torque the spark plug properly.
Spark plug torque:
12.5 N.m (1.25 Kgf.m, 9 lbf.ft)
NOTE:
If a torque wrench is not available when you are installing a
spark plug, a good estimate of the correct torque is 1/4 to
1/2 turn past finger tight. Have the spark plug torqued to
the correct value as soon as possible with a torque wrench.

!
Drive chain slack adjustment
1. Locknut 2. Adjusting bolt
1. Loosen the rear brake pedal free play adjusting nut.
2. Loosen the axle nut.
3. Loosen the chain adjusting locknuts on each chainpuller. To tighten the chain, turn the chain adjusting nuts
in direction  .To loosen the chain turn the chain
adjusting nuts in direction  and push the wheel
forward. Turn each chain adjusting nut exactly the same
amount to maintain correct axle alignment. There are
marks on each chain puller. Use these marks to align
the rear wheel. Too little chain slack will overload the engine and other vital
parts. Keep the slack within the specified limits.
To maintain correct axle alignment, Ensure the notch on
the adjuster is on the same mark on left and right side
4. After adjusting, be sure to tighten each chain adjusting
locknut. The tighten the axle nut to the specified torque
Axle nut torque: 91 N.m (9.1 Kgf.m, 66 lbf.ft)
Locknut torque: 15 N.m (1.5 Kgf.m, 11 lbf.ft)
5. Adjust the free play in the brake pedal.
Check the operation of the brake light after adjusting
the rear brake.
CAUTION:
CAUTION:
!
Drive chain slack adjustment
1. Locknut 2. Adjusting bolt
1. Loosen the rear brake pedal free play adjusting nut.
2. Loosen the axle nut.
3. Loosen the chain adjusting locknuts on each chain puller. To tighten the chain, turn the chain adjusting nuts
in direction  .To loosen the chain turn the chain
adjusting nuts in direction  and push the wheel
forward. Turn each chain adjusting nut exactly the same
amount to maintain correct axle alignment. There are
marks on each chain puller. Use these marks to align
the rear wheel. Too little chain slack will overload the engine and other vital
parts. Keep the slack within the specified limits.
To maintain correct axle alignment, Ensure the notch on
the adjuster is on the same mark on left and right side
4. After adjusting, be sure to tighten each chain adjusting
locknut. The tighten the axle nut to the specified torque
Axle nut torque: 91 N.m (9.1 Kgf.m, 66 lbf.ft)
Locknut torque: 15 N.m (1.5 Kgf.m, 11 lbf.ft)
5. Adjust the free play in the brake pedal.
Check the operation of the brake light after adjusting
the rear brake.
CAUTION:
CAUTION:

6-23 Drive chain lubrication
The chain consists of many parts which work with each
other. If the chain is not maintained properly, it will wear out
quickly. Therefore, the chain must be serviced regularly.
This service is especially necessary when riding in dusty
areas.
1. Use Yamaha Chain and Cable Lube or any
brands of spray-type chain lubricant. First,
remove all dirt and mud from the chain with a
brush or cloth, then spray lubricant between both
rows of side plates and on all center rollers. The
chain should be lubricated every 500 km (300 mi).
2. To clean the chain, remove it from the machine,
dip it in solvent, and clean out as much dirt as
possible. Take the chain out of the solvent and
dry it. Immediately lubricate the chain to prevent
it from rusting.Cable inspection and lubrication
Damage to the outer housing of cables may allow
internal rusting and cause interfere with cable
movement. Replace damaged cables as soon as
possible to prevent unsafe conditions.
Lubricate the inner cable and the cable end. If it does not
operate smoothly, ask a Yamaha dealer to replace them.
RECOMMENDED LUBRICANT:
Engine oil SAE 20W50
WARNING:
6-23 Drive chain lubrication
The chain consists of many parts which work with each
other. If the chain is not maintained properly, it will wear out
quickly. Therefore, the chain must be serviced regularly.
This service is especially necessary when riding in dusty
areas.
1. Use Yamaha Chain and Cable Lube or any
brands of spray-type chain lubricant. First,
remove all dirt and mud from the chain with a
brush or cloth, then spray lubricant between both
rows of side plates and on all center rollers. The
chain should be lubricated every 500 km (300 mi).
2. To clean the chain, remove it from the machine,
dip it in solvent, and clean out as much dirt as
possible. Take the chain out of the solvent and
dry it. Immediately lubricate the chain to prevent
it from rusting.Cable inspection and lubrication
Damage to the outer housing of cables may allow
internal rusting and cause interfere with cable
movement. Replace damaged cables as soon as
possible to prevent unsafe conditions.
Lubricate the inner cable and the cable end. If it does not
operate smoothly, ask a Yamaha dealer to replace them.
RECOMMENDED LUBRICANT:
Engine oil SAE 20W50
WARNING:

6-24
Throttle cable and grip lubrication
The throttle twist grip assembly should be greased at the
time the cable is lubricated, since the grip must be removed
to get at the end of the throttle cable.
After removing the screws, hold the end of the cable up in
the air and put in several drops of lubricant. With the throttle
grip disassembled, coat the metal surface of the grip
assembly with a suitable all-purpose grease.Brake and shift pedals
Lubricate the pivoting parts.
RECOMMENDED LUBRICANT: Engine oil SAE 20W50
Brake and clutch levers
Lubricate the pivoting parts. RECOMMENDED LUBRICANT: Engine oil SAE 20W50
Sidestand
Lubricate the pivoting parts. Check to see that the sidestand
moves up and down smoothly. RECOMMENDED LUBRICANT: Engine oil SAE 20W50
WARNING:
If the sidestand does not move smoothly, consult a
Yamaha dealer.
CAUTION:
6-24
Throttle cable and grip lubrication
The throttle twist grip assembly should be greased at the
time the cable is lubricated, since the grip must be removed
to get at the end of the throttle cable.
After removing the screws, hold the end of the cable up in
the air and put in several drops of lubricant. With the throttle
grip disassembled, coat the metal surface of the grip
assembly with a suitable all-purpose grease. Brake and shift pedals
Lubricate the pivoting parts.
RECOMMENDED LUBRICANT: Engine oil SAE 20W50
Brake and clutch levers
Lubricate the pivoting parts. RECOMMENDED LUBRICANT: Engine oil SAE 20W50
Sidestand
Lubricate the pivoting parts. Check to see that the sidestand
moves up and down smoothly. RECOMMENDED LUBRICANT: Engine oil SAE 20W50
WARNING:
If the sidestand does not move smoothly, consult a
Yamaha dealer.
CAUTION:

6-26
Periodically inspect the condition of the steering. Worn out
or loose steering bearings may be dangerous. Place a stand
under the engine to raise the front wheel off the ground.
Hold the lower end of the front forks and try to move them
forward and backward. If any free play can be felt, ask a
Yamaha dealer to inspect and adjust the steering. Inspection
is easier if the front wheel is removed.
Securely support the motorcycle so there is no danger
of it falling over.Wheel bearings
If there is play in the front or rear wheel hub or if the wheel
does not turn smoothly, have a Yamaha dealer inspect the
wheel bearings. The wheel bearings should be inspected
according to the Maintenance Schedule.
Steering inspection
WARNING:
6-26
Periodically inspect the condition of the steering. Worn out
or loose steering bearings may be dangerous. Place a stand
under the engine to raise the front wheel off the ground.
Hold the lower end of the front forks and try to move them
forward and backward. If any free play can be felt, ask a
Yamaha dealer to inspect and adjust the steering. Inspection
is easier if the front wheel is removed.
Securely support the motorcycle so there is no danger
of it falling over. Wheel bearings
If there is play in the front or rear wheel hub or if the wheel
does not turn smoothly, have a Yamaha dealer inspect the
wheel bearings. The wheel bearings should be inspected
according to the Maintenance Schedule.
Steering inspection
WARNING: