2003 YAMAHA TTR125 engine

3 - 23
INSP
ADJ
FRONT FORK INSPECTION/
REAR SHOCK ABSORBER ASSEMBLY INSPECTION/
REAR SHOCK ABSORBER SPRING PRELOAD ADJUSTMENT
EC36C000
FRONT FORK INSPECTION
1. Inspect:
Front 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:
Swingarm 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:
Left side cover
3. Loosen:
Locknut 1
4. Adjust:
Spring 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 - 25
INSP
ADJSPOKES INSPECTION AND TIGHTENING/WHEEL INSPECTION/
STEERING HEAD INSPECTION AND ADJUSTMENT
SPOKES INSPECTION AND TIGHTENING
1. Inspect:
Spokes 1
Bend/damage → Replace.
Loose spoke → Retighten.
2. Tighten:
Spokes
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:
Wheel runout
Elevate the wheel and turn it.
Abnormal runout → Replace.
2. Inspect:
Bearing 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:
Steering shaft
Grasp the bottom of the forks and gen-
tly rock the fork assembly back and
forth.
Free play → Adjust steering head.

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INSP
ADJ
ELECTRICAL/SPARK PLUG INSPECTION
EC370000
ELECTRICAL
EC371001
SPARK PLUG INSPECTION
1. Remove:
Spark plug
2. Inspect:
Electrode 1
Wear/damage → Replace.
Insulator 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:
Plug 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:
Spark plug
NOTE:
Before installing a spark plug, clean the gas-
ket surface and plug surface.
Finger-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 - 5
ENG

CARBURETOR
HANDLING NOTE
At high altitudes, the atmospheric pressure is
lower. This can make the fuel mixture too rich,
leading to such problems as fouled.
Spark plugs and slow response at high engine
speeds. A special part, High Altitude Main Jet
1
#102.5 (620-1423A-71-A0) is available to
correct this.
EC463000
REMOVAL POINTS
Throttle valve
1. Remove:

Throttle valve
1


Spring (throttle valve)
2


Carburetor top cover
3


Throttle cable
4

NOTE:

While compressing the spring (throttle valve),
disconnect the throttle cable.
Pilot air screw
1. Remove:

Pilot air screw
1

NOTE:

To optimize the fuel flow at a smaller throttle
opening, each machine’s pilot air screw has
been individually set at the factory. Before
removing 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.

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ENGCARBURETOR
3. Install:
Carburetor top cover 1
Starter plunger 2
Air vent hose 3
Over flow hose 4
Fuel hose 5
NOTE:
Align the slit a of the throttle valve with the tab
b of the carburetor body.
4. Adjust:
Idle speed
Refer to “ENGINE IDLING SPEED
ADJUSTMENT” section in the CHAP-
TER 3.

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ENGCYLINDER HEAD
CYLINDER HEAD
CYLINDER HEAD SIDE COVER AND TAPPET COVER
Extent of removal:1 Cylinder head side cover and tappet cover removal
Extent of removal Order Part name Q’ty Remarks
CYLINDER HEAD SIDE COVER
AND TAPPET COVER
REMOVAL
Preparation for removal Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Muffler Refer to “MUFFLER” section.
Carburetor Refer to “CARBURETOR” section.
CDI unit Remove from the frame.
1 Engine bracket 1
2 Spark plug 1
3 Cylinder head side cover 1
4 Tappet cover 2
5 Crankshaft end accessing screw 1
6Timing mark accessing screw
1
1

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ENGCYLINDER HEAD
Warpage limit:
0.03 mm (0.0012 in)
If the warpage is out of specification,
resurface the cylinder head.
Place #400 ~ 600 grit wet sandpaper on
the surface plate, and re-surface the head
using a figure-eight sanding pattern.
NOTE:
Rotate the cylinder head several times to
avoid removing too much material from one
side.
ASSEMBLY AND INSTALLATION
Cylinder head
1. Install:
Dowel pin 1
Gasket 2 New
2. Install:
Cylinder head
Copper washer
Bolt (cylinder head)
NOTE:
Apply Quick gasket® (YAMAHA Bond
No.1215) on end of the cylinder head bolts
(M6), as shown.
Apply the engine oil on the contact surfaces of
the bolts (cylinder head) and copper washers.
Follow the numerical order shown in the illus-
tration. Tighten the bolts in two stages.
Quick gasket®:
ACC-QUICK-GS-KT
YAMAHA Bond No.1215:
90890-85505
T R..M8 22 Nm (2.2 m · kg, 16 ft · lb)
M6 10 Nm (1.0 m · kg, 7.2 ft · lb)