2000 YAMAHA TTR125 engine

3 - 10
INSP
ADJOIL PRESSURE INSPECTION/PILOT AIR SCREW
ADJUSTMENT/ENGINE IDLING SPEED ADJUSTMENT
OIL PRESSURE INSPECTION
1. Check:
lOil pressure
Checking steps:
lSlightly loosen the oil pressure check bolt
1.
lStart the engine and keep it idling until oil
starts to seep from the oil pressure check
bolt. If no oil comes out after one minute,
turn the engine off so it will not seize.
lCheck oil passages and oil pump for dam-
age or leakage.
lStart the engine after solving the prob-
lem(s) and recheck the oil pressure.
lTighten the oil pressure check bolt.
T R..
Oil pressure check bolt:
7 Nm (0.7 m • kg, 5.1 ft • lb)
PILOT AIR SCREW ADJUSTMENT
1. Adjust:
lPilot air screw 1
Adjustment steps:
lScrew in the pilot air screw until it is lightly
seated.
lBack out by the specified number of turns.
Pilot air screw:
2-1/2 ~ 3-1/2 turns out (example)
NOTE:
To optimize the fuel flow at a smaller throt-
tle opening, each machine’s pilot air screw
has been individually set at the factory.
Before adjusting the pilot air screw, turn it in
fully and count the number of turns. Record
this number as the factory-set number of
turns out.
ENGINE IDLING SPEED ADJUSTMENT
1. Start the engine and thoroughly warm it
up.
2. Attach:
lInductive tachometer
To spark plug lead.
3. Adjust:
lEngine idling speed

3 - 11
INSP
ADJ
VALVE CLEARANCE INSPECTION AND ADJUSTMENT
VALVE CLEARANCE INSPECTION AND
ADJUSTMENT
NOTE:
lThe valve clearance should be adjusted
when the engine is cool to the touch.
lThe piston must be at Top Dead Center
(T.D.C.) on compression stroke to check or
adjust the valve clearance.
1. Remove:
lSeat
lFuel tank
Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section in the CHAPTER 4. Adjustment steps:
lAdjust the pilot air screw.
Refer to “PILOT AIR SCREW ADJUST-
MENT” section.
lTurn the throttle stop screw 1 until the
specified engine idling speed.
To increase idling speed ®
Turn the throttle stop screw 1 in a.
To decrease idling speed ®
Turn the throttle stop screw 1 out b.
Inductive tachometer:
YU-08036-B/90890-03113
Engine idling speed:
1,300 ~ 1,500 r/min
2. Remove:
lSpark plug
lIntake tappet cover 1
lExhaust tappet cover 2
lO-ring
3. Remove:
lTiming mark accessing screw 1
lCrankshaft end accessing screw 2
lO-ring

3 - 14
INSP
ADJ
SPARK ARRESTER CLEANING (For USA)
SPARK ARRESTER CLEANING (For USA)
WARNING
lBe sure the exhaust pipe and muffler are
cool before cleaning the spark arrester.
lDo not start the engine when cleaning the
exhaust system.
1. Remove:
lBolt (spark arrester) 1
2. Remove:
lSpark arrester 1
Pull the spark arrester out of the muf-
fler.
3. Clean:
lSpark arrester
Tap the spark arrester lightly, then use
a wire brush to remove any carbon
deposits.
4. Install:
lSpark arrester
Insert the spark arrester into the muffler
and align the bolt holes.
lBolt (spark arrester)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)

3 - 18
INSP
ADJ
DRIVE CHAIN SLACK ADJUSTMENT
6. Lubricate:
lDrive chain
Drive chain lubricant:
SAE 10W-30 motor oil or suit-
able chain lubricants
DRIVE CHAIN SLACK ADJUSTMENT
1. Elevate the rear wheel by placing the
suitable stand under the engine.
2. Check:
lDrive chain slack a
In the center between the drive axle
and rear wheel axle.
Out of specification ® Adjust.
NOTE:
Before checking and/or adjusting, rotate the
rear wheel through several revolutions and
check the slack several times to find the tight-
est point. Check and/or adjust chain slack with
rear wheel in this “tight chain” position.
Drive chain slack:
35 ~ 60 mm (1.4 ~ 2.4 in)
3. Adjust:
lDrive chain slack
Drive chain slack adjustment steps:
lLoosen the axle nut 1.
lTurn both drive chain pullers 2 the same
amount a and adjust them to the stopper
in the same position so that the drive
chain slack is within the specified limits.
lTighten the axle nut while pushing down
the drive chain.
T R..
Axle nut:
60 Nm (6.0 m • kg, 43 ft • lb)
CAUTION:
Too small chain slack will overload the
engine and other vital parts; keep the
slack within the specified limits.

3 - 19
INSP
ADJ
FRONT FORK INSPECTION/
REAR SHOCK ABSORBER ASSEMBLY INSPECTION/
REAR SHOCK ABSORBER SPRING PRELOAD ADJUSTMENT
EC36C000
FRONT FORK INSPECTION
1. Inspect:
lFront fork smooth action
Operate the front brake and stroke the
front fork.
Unsmooth action/oil leakage ® Repair
or replace.
REAR SHOCK ABSORBER ASSEMBLY
INSPECTION
1. Inspect:
lSwingarm smooth action
Abnormal noise/unsmooth action ®
Grease the pivoting points or repair the
pivoting points.
Damage/oil leakage ® Replace.
REAR SHOCK ABSORBER SPRING
PRELOAD ADJUSTMENT
1. Elevate the rear wheel by placing the
suitable stand under the engine.
2. Remove:
lLeft side cover
3. Loosen:
lLocknut 1
4. Adjust:
lSpring preload
By turning the adjuster 2.
Stiffer ®Increase the spring preload.
(Turn the adjuster 2 in.)
Softer ®Decrease the spring preload.
(Turn the adjuster 2 out.)
Spring length (installed) a:
Standard length Extent of adjustment
165 mm (6.50 in)155 ~ 175 mm
(6.10 ~ 6.89 in)

3 - 21
INSP
ADJSPOKES INSPECTION AND TIGHTENING/WHEEL INSPECTION/
STEERING HEAD INSPECTION AND ADJUSTMENT
SPOKES INSPECTION AND TIGHTENING
1. Inspect:
lSpokes 1
Bend/damage ® Replace.
Loose spoke ® Retighten.
2. Tighten:
lSpokes
NOTE:
Be sure to retighten these spokes before and
after break-in. After a practice check spokes
for looseness.
T R..Front 2 Nm (0.2 m · kg, 1.4 ft · lb)
Rear 3 Nm (0.3 m · kg, 2.2 ft · lb)
EC36T000
WHEEL INSPECTION
1. Inspect:
lWheel runout
Elevate the wheel and turn it.
Abnormal runout ® Replace.
2. Inspect:
lBearing free play
Exist play ® Replace.
STEERING HEAD INSPECTION AND
ADJUSTMENT
1. Elevate the front wheel by placing a suit-
able stand under the engine.
2. Check:
lSteering shaft
Grasp the bottom of the forks and gen-
tly rock the fork assembly back and
forth.
Free play ® Adjust steering head.

3 - 25
INSP
ADJ
ELECTRICAL/SPARK PLUG INSPECTION
EC370000
ELECTRICAL
EC371001
SPARK PLUG INSPECTION
1. Remove:
lSpark plug
2. Inspect:
lElectrode 1
Wear/damage ® Replace.
lInsulator color 2
Normal condition is a medium to light
tan color.
Distinctly different color ® Check the
engine condition.
NOTE:
When the engine runs for many hours at low
speeds, the spark plug insulator will become
sooty, even if the engine and carburetor are in
good operating condition.
3. Measure:
lPlug gap a
Use a wire gauge or thickness gauge.
Out of specification ® Regap.
4. Clean the plug with a spark plug cleaner
if necessary.
Spark plug gap:
0.6 ~ 0.7 mm (0.02 ~ 0.03 in)
Standard spark plug:
CR7HSA (NGK)
U22FSR-U (DENSO)
5. Tighten:
lSpark plug
NOTE:
lBefore installing a spark plug, clean the gas-
ket surface and plug surface.
lFinger-tighten a the spark plug before
torquing to specification b.
T R..13 Nm (1.3 m · kg, 9.4 ft · lb)

4 - 1
ENG

EC400000
ENGINE
EC4R0000
SEAT, FUEL TANK AND SIDE COVERS
Extent of removal:
1
Seat removal
2
Fuel tank removal
3
Side covers removal
4
Number plate removal
Extent of removal Order Part name Q’ty Remarks
Preparation for removal
SEAT, FUEL TANK AND SIDE
COVERS REMOVAL
Turn the fuel cock to “OFF”.
1 Seat 1
2 Air scoop (left and right) 2
3 Fuel hose 1 Remove on fuel tank side.
4 Fitting band 1
5 Bolt (fuel tank) 2
6 Fuel tank 1
7 Left side cover 1
8 Right side cover 1
9Number plate
1
13
4
2
3

SEAT, FUEL TANK AND SIDE COVERS
4