2000 YAMAHA TTR125 engine

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:
l
Throttle valve
1

l
Spring (throttle valve)
2

l
Carburetor top cover
3

l
Throttle cable
4

NOTE:

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

4 - 11
ENGCARBURETOR
3. Install:
lCarburetor top cover 1
lStarter plunger 2
lAir vent hose 3
lOver flow hose 4
lFuel hose 5
NOTE:
Align the slit a of the throttle valve with the tab
b of the carburetor body.
4. Adjust:
lIdle 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
6 Timing mark accessing screw 1
1

4 - 16
ENGCYLINDER HEAD
Warpage limit:
0.03 mm (0.0012 in)
lIf the warpage is out of specification,
resurface the cylinder head.
lPlace # 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:
lDowel pin 1
lGasket 2 New
2. Install:
lCylinder head
lCopper washer
lBolt (cylinder head)
NOTE:
lApply Quick gasket® (Yamaha bond No.
1215) on end of the cylinder head bolts (M6),
as shown.
lApply the engine oil on the contact surfaces of
the bolts (cylinder head) and copper washers.
lFollow 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)

4 - 19
ENGCYLINDER HEAD
9. Check:
lValve clearance
Out of specification ® Adjust.
Refer to “VALVE CLEARANCE
INSPECTION AND ADJUSTMENT”
section in CHAPTER 3.
10. Apply:
lEngine oil
To camshaft.
11. Install:
lTappet cover 1
lCylinder head side cover 2
T R..18 Nm (1.8 m · kg, 13 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
12. Install:
lTiming mark accessing screw 1
lCrankshaft end accessing screw 2
T R..7 Nm (0.7 m · kg, 5.1 ft · lb)
T R..7 Nm (0.7 m · kg, 5.1 ft · lb)
13. Install:
lSpark plug
lEngine bracket
T R..13 Nm (1.3 m · kg, 9.4 ft · lb)
T R..40 Nm (4.0 m · kg, 29 ft · lb)

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ENGCAMSHAFT AND ROCKER ARMS
Rocker arms and rocker arm shafts
1. Inspect:
lCam lobe contact surface a
lAdjuster surface 1
Wear/pitting/scratches/blue discolora-
tion ® Replace.
Measurement steps:
lMeasure the inside diameter a of the
rocker arm holes.
Out of specification ® Replace.
Inside diameter (rocker arm):
10.000 ~ 10.015 mm
(0.3937 ~ 0.3943 in)
: 10.03 mm (0.3949 in)
lMeasure the outside diameter b of the
rocker arm shafts.
Out of specification ® Replace.
Outside diameter
(rocker arm shaft):
9.981 ~ 9.991 mm
(0.3930 ~ 0.3933 in)
: 9.95 mm (0.3917 in)
ASSEMBLY AND INSTALLATION
1. Apply:
lMolybdenum disulfide oil
(onto the camshaft cam lobe and rocker
arm hole)
lEngine oil
(onto the camshaft bearing)
2. Install:
lRocker arms
lCamshaft 1
3. Apply:
lEngine oil
(onto the rocker arm shaft)
4. Install:
lRocker arm shaft

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ENGVALVES AND VALVE SPRINGS
2. Measure:
lCompressed spring force a
Out of specification ® Replace.
bInstalled length
3. Measure:
lSpring tilt a
Out of specification ® Replace.
Compressed spring force:
Intake:
14.0 ~ 16.1 kg at 25.6 mm
(30.86 ~ 35.49 lb at 1.01 in)
Exhaust:
14.0 ~ 16.1 kg at 25.6 mm
(30.86 ~ 35.49 lb at 1.01 in)
Spring tilt limit:
Intake:
2.5˚/1.4 mm (0.06 in)
Exhaust:
2.5˚/1.4 mm (0.06 in)
ASSEMBLY AND INSTALLATION
Valve
1. Apply:
lEngine oil
(onto the valve stem and valve stem
seal)
2. Install:
lValve spring seats 1
lValve stem seals 2
lValves 3
lValve springs 4
lValve spring retainers 5
NOTE:
lMake sure that each valve is installed in its
original place.
lInstall the valve springs with the larger pitch
a facing upwards.
bSmaller pitch
New

4 - 38
ENGCYLINDER AND PISTON
ASSEMBLY AND INSTALLATION
Piston ring and piston
1. Install:
lPiston rings
(onto the piston)
NOTE:
lBe sure to install the 2nd piston ring so that
the manufacturer’s mark or number are
located on the upper side of the ring.
lLubricate the piston and piston rings liberally
with engine oil.
2. Position:
lTop ring
l2nd ring
lOil ring
Offset the piston ring end gaps as
shown.
aTop ring end
b2nd ring end
cOil ring end (upper)
dOil ring end (lower)
3. Install:
lPiston 1
lPiston pin 2
lPiston pin clips 3
NOTE:
lApply engine oil onto the piston pin, piston
rings and piston.
lBe sure that the arrow mark a on the piston
points to the exhaust side of the engine.
lBefore installing the piston pin clip, cover the
crankcase with a clean rag to prevent the
piston pin clip from falling into the crankcase.
lWhen removing the piston pin clip, pop it out
using the small opening b.
4. Lubricate:
lPiston
lPiston rings
lInside of cylinder
NOTE:
Apply a liberal coating of engine oil.
New