2000 YAMAHA SR125 engine

PERIODIC MAINTENANCE AND MINOR REPAIR
6-6
6
EAU01833
Spark plugRemoval
1. Remove the spark plug cap.2. Use the spark plug wrench in the
tool kit to remove the spark plug as
shown.
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 insulator
around the center electrode is a medi-
um-to-light tan color for a motorcycle
that is being ridden normally.
Do not attempt to diagnose such prob-
lems yourself. Instead, take the motor-
cycle to a Yamaha dealer. You should
periodically remove and inspect thespark plug because heat and deposits
will cause any spark plug to slowly
break down and erode. If electrode ero-
sion becomes excessive, or if carbon
and other deposits are excessive, you
should replace the spark plug with the
specified plug.1. Spark plug cap
1. Spark plug wrench
Specified spark plug:
DR8EA (NGK)
E_3mw.book Page 6 Monday, February 5, 2001 9:54 AM

PERIODIC MAINTENANCE AND MINOR REPAIR
6-8
6
EAU01093*
Engine oilOil level inspection
1. Place the motorcycle on the cen-
terstand. Warm up the engine for
several minutes.NOTE:@ Be sure the motorcycle is positioned
straight up when checking the oil level.
A slight tilt toward the side can result in
false readings. @
2. With the engine stopped, check
the oil level through the level win-
dow located at the lower part of
the right side crankcase cover.NOTE:@ Wait a few minutes until the oil level
settles before checking. @3. The oil level should be between
the maximum level and minimum
level marks. If the level is low, fill
the engine with sufficient oil to
raise it to the specified level.Engine oil replacement and oil filter
element cleaning
1. Warm up the engine for a few min-
utes.
2. Stop the engine. Place an oil pan
under the engine and remove the
oil filler cap.
3. Remove the drain bolt and drain
the oil.
EC000070*
CAUTION:@ When removing the oil drain bolt,
the O-ring, compression spring, and
oil strainer will fall out. Take care not
to lose these parts. @
1. Oil level window
2. Maximum level mark
3. Minimum level mark
1. Engine oil drain bolt A
E_3mw.book Page 8 Monday, February 5, 2001 9:54 AM

PERIODIC MAINTENANCE AND MINOR REPAIR
6-9
6 4. Remove the filter cover screws,
drain bolt and the oil filter cover
and oil filter.
5. Clean the oil filter and strainer with
solvent. Replace if necessary.
6. Check the O-rings. If damaged, re-
place it.
7. Install the drain bolt, filter cover
screws and drain bolt. Then tight-
en to the specified torque.
NOTE:@ Make sure the O-ring is seated proper-
ly. @
EC000071*
CAUTION:@ Before reinstalling the oil drain bolt,
do not forget to install the O-ring,
compression spring, and oil strainer
in position. @8. Fill engine with oil. Install the oil fill-
er cap and tighten.
EC000066
CAUTION:@ l
Do not put in any chemical addi-
tives. Engine oil also lubricates
the clutch and additives could
cause clutch slippage.
l
Be sure no foreign material en-
ters the crankcase.
@9. Start the engine and warm up for a
few minutes. While warming up,
check for oil leakage. If oil leakage
is found, stop the engine immedi-
ately and check for the cause.
10. Stop the engine and check the oil
level.
1. Filter cover screw (´ 2)
2. Engine oil drain bolt B
Tightening torque:
Drain bolt A:
43 Nm (4.3 m·kg)
Filter cover screw:
7 Nm (0.7 m·kg)
Drain bolt B:
10 Nm (1.0 m·kg)
Recommended oil:
See page 8-1.
Oil quantity:
Total amount:
1.3 L
Periodic oil change:
1.0 L
With oil filter replacement:
1.1 L
E_3mw.book Page 9 Monday, February 5, 2001 9:54 AM

PERIODIC MAINTENANCE AND MINOR REPAIR
6-10
6
EAU01094
Air filterThe air filter should be cleaned at the
specified intervals. It should be cleaned
more frequently if you are riding in un-
usually wet or dusty areas.
1. Remove panel A. (See page 6-5
for panel removal and installation
procedures.)
2. Remove the air filter case fitting
screws and the air filter case cov-
er.
3. Remove the air filter from its case
and clean it with solvent. After
cleaning, remove the remaining
solvent by squeezing the air filter.4. Apply the recommended oil to the
entire surface of the filter and
squeeze out the excess oil. It
should be wet but not dripping.
5. Install the air filter in its case.
6. Install panel A.
EC000085
CAUTION:@ l
Make sure the air filter is prop-
erly seated in the filter case.
l
The engine should never be run
without the air filter installed.
Excessive piston and/or cylin-
der wear may result.
@
1. Air filter
2. Steel net
Recommended oil:
Same as engine oil
1. Rubber gasket
E_3mw.book Page 10 Monday, February 5, 2001 9:54 AM

PERIODIC MAINTENANCE AND MINOR REPAIR
6-11
6
EAU00629
Carburetor adjustmentThe carburetor is a vital part of the en-
gine and requires very sophisticated
adjustment. Most adjustments should
be left to a Yamaha dealer who has the
professional knowledge and experi-
ence to do so. However, the following
may be serviced by the owner as part
of routine maintenance.
EC000094
CAUTION:@ The carburetor was set at the
Yamaha factory after many tests. If
the settings are changed, poor en-
gine performance and damage may
result. @
EAU01168
Idle speed adjustmentNOTE:@ A diagnostic tachometer must be used
for this procedure. @1. Attach the tachometer. Start the
engine and warm it up for a few
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 quick-
ly responds to the throttle.2. Set the idle to the specified engine
speed by adjusting the throttle
stop screw. Turn the screw in di-
rection
a to increase engine
speed and in direction
b to de-
crease engine speed.
NOTE:@ If the specified idle speed cannot be
obtained by performing the above ad-
justment, consult a Yamaha dealer. @1. Throttle stop screwStandard idle speed:
1,300 ~ 1,400 r/min
E_3mw.book Page 11 Monday, February 5, 2001 9:54 AM

PERIODIC MAINTENANCE AND MINOR REPAIR
6-12
6
EAU00634
Throttle cable free play
adjustmentNOTE:@ Before checking the throttle cable free
play, the engine idling speed should be
adjusted. @Adjust the throttle cable by turning the
adjusting nut so that specified free play
at the throttle grip is obtained.1. Loosen the locknut.
2. Turn the adjusting nut in
direction
a to increase free play
and in direction
b to decrease
free play.
3. Tighten the locknut.
EAU00636
Cam chain adjustmentThe cam chain becomes loose with
use, resulting in improper valve timing
and engine noise. To prevent this, the
cam chain tensioner must be adjusted
regularly. This adjustment, however,
should be left to a professional
Yamaha service technician.
a. Free playFree play:
3 ~ 5 mm
1. Adjusting nut
2. Locknut
E_3mw.book Page 12 Monday, February 5, 2001 9:54 AM

PERIODIC MAINTENANCE AND MINOR REPAIR
6-13
6
EAU00637
Valve clearance adjustmentThe correct valve clearance changes
with use, resulting in improper fuel/air
supply or engine noise. To prevent this,
the valve clearance must be adjusted
regularly. This adjustment however,
should be left to a professional
Yamaha service technician.
EAU00647
TiresTo ensure maximum performance,
long service, and safe operation, note
the following:
Tire air pressure
Always check and adjust the tire pres-
sure before operating the motorcycle.
EW000082
WARNING
@ Tire inflation pressure should be
checked and adjusted when the
temperature of the tire equals the
ambient air temperature. Tire infla-
tion pressure must be adjusted ac-
cording to total weight of cargo,
rider, passenger, and accessories
(fairing, saddlebags, etc. if approved
for this model), and vehicle speed. @
CE-32EMaximum load* 160 kg
Cold tire pressure Front Rear
Up to 90 kg*175 kPa
(1.75 kg/cm
2,
1.75 bar)200 kPa
(2.00 kg/cm
2,
2.00 bar)
90 kg load ~
Maximum load*175 kPa
(1.75 kg/cm
2,
1.75 bar)225 kPa
(2.25 kg/cm
2,
2.25 bar)
* Load is the total weight of cargo, rider, passenger
and accessories.
E_3mw.book Page 13 Monday, February 5, 2001 9:54 AM

PERIODIC MAINTENANCE AND MINOR REPAIR
6-22
6
EAU01533
Drive chain slack adjustment1. Loosen the rear brake adjusting
nut.
2. Loosen the wheel axle nut.3. To tighten the chain, turn the chain
adjusting plates in direction
a.
To loosen the chain, turn the chain
adjusting plates in direction
b and
push the wheel forward. Turn each
chain adjusting plate to exactly the
same position to maintain correct
axle alignment.
EC000096
CAUTION:@ Too little chain slack will overload
the engine and other vital parts.
Keep the slack within the specified
limits. @
4. Tighten the wheel axle nut to the
specified torque.
5. Adjust the brake pedal free play.
EW000103
WARNING
@ Check the operation of the brake
light after adjusting the rear brake. @
1. Adjusting nut
1. Axle nut
2. Chain adjusting plate
Tightening torque:
Wheel axle nut:
65 Nm (6.5 m·kg)
E_3mw.book Page 22 Monday, February 5, 2001 9:54 AM