2010 YAMAHA YZ125LC Owners Manual

4-5
RADIATOR
RADIATOR
REMOVING THE RADIATOR
Order Part name Q'ty Remarks
Drain the coolant.Refer to "CHANGING THE COOLANT" sec-
tion in the CHAPTER 3.
Seat and fuel tankRefer to "SEAT, FUEL TANK AND SIDE
COVERS" section.
1 Radiator guard 2
2 Radiator hose clamp (radiator hose 1, 3) 2 Only loosening.
3 Radiator hose 2 1
4 Left radiator 1
5 Radiator hose 4 1
6 Right radiator 1
7 Radiator hose 1 1
8 Radiator hose 3 1
9 Radiator breather hose 1
10 Nm (1.0 m kg, 7.2 ft lb)
2 Nm (0.2 m kg, 1.4 ft lb)
10 Nm (1.0 m kg, 7.2 ft lb)
10 Nm (1.0 m kg, 7.2 ft lb)
2 Nm (0.2 m kg, 1.4 ft lb)

4-6
RADIATOR
HANDLING NOTE
Do not remove the radiator cap
when the engine and radiator are
hot. Scalding hot fluid and steam
may be blown out under pressure,
which could cause serious injury.
When the engine has cooled, open
the radiator cap by the following
procedure:
Place a thick rag, like a towel, over
the radiator cap, slowly rotate the
cap counterclockwise to the de-
tent. This procedure allows any re-
sidual pressure to escape. When
the hissing sound has stopped,
press down on the cap while turn-
ing counterclockwise and remove
it.
CHECKING THE RADIATOR
1. Inspect:
• Radiator core "1"
Obstruction→Blow out with com-
pressed air through rear of the ra-
diator.
Bent fin→Repair/replace.
INSTALLING THE RADIATOR
1. Install:
• Radiator breather hose "1"
• Radiator hose 3 "2"
• Radiator hose 1 "3"
To right radiator "4".
Clamp the radiator hose in the direc-
tion as shown.
2. Install:
• Right radiator "1"
• Washer "2"
• Bolt (right radiator) "3"
• Radiator hose 4 "4"
Refer to "CABLE ROUTING DIA-
GRAM" section in the CHAPTER
2.
3. Install:
• Left radiator "1"
• Washer "2"
• Bolt (left radiator) "3"
• Radiator hose 2 "4"
Refer to "CABLE ROUTING DIA-
GRAM" section in the CHAPTER
2.
4. Tighten:
• Radiator hose clamp 1, 3 "5"
5. Install:
• Radiator guard "1"
• Bolt (radiator guard) "2"
Fit the hook "a" on the inner side first
into the radiator.
Radiator hose 3:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Radiator hose 1:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Bolt (right radiator):
10 Nm (1.0 m•kg, 7.2
ft•lb)
Radiator hose 4:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Bolt (left radiator):
10 Nm (1.0 m•kg, 7.2
ft•lb)
Radiator hose 2:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Radiator hose clamp 1, 3:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Bolt (radiator guard):
10 Nm (1.0 m•kg, 7.2
ft•lb)

4-7
CARBURETOR AND REED VALVE
CARBURETOR AND REED VALVE
REMOVING THE CARBURETOR AND REED VALVE
Order Part name Q'ty Remarks
Fuel tank Refer to "SEAT, FUEL TANK AND SIDE
COVERS" section.
1 Clamp (carburetor joint) 2 Loosen the screw (carburetor joint).
2 Carburetor 1
3 Carburetor joint 1
4 Reed valve assembly 1
5 Stopper (reed valve) 2
6 Reed valve 2
10 Nm (1.0 m kg, 7.2 ft lb)
2 Nm (0.2 m kg, 1.4 ft lb)
2 Nm (0.2 m kg, 1.4 ft lb)
1 Nm (0.1 m kg, 0.7 ft lb)

4-8
CARBURETOR AND REED VALVE
DISASSEMBLING THE CARBURETOR
Order Part name Q'ty Remarks
1 Mixing chamber top 1 Refer to removal section.
2 Throttle valve 1
3 Needle holder 1
4 Jet needle 1
5 Float chamber 1
6 Needle jet cover 1
7 Float pin 1
8 Float 1
9 Valve seat 1
10 Main jet 1
11 Main jet holder 1
12 Pilot jet 1
13 Starter plunger 1
14 Throttle stop screw 1
15 Pilot air screw 1
4 Nm (0.4 m kg, 2.9 ft lb)

4-9
CARBURETOR AND REED VALVE
HANDLING NOTE
Do not disassemble the venturi
block "1" and main nozzle "2" be-
cause it will cause a drop in carbu-
retor performance.
REMOVING THE THROTTLE
VALVE
1. Remove:
• Throttle valve "1"
• Ring "2"
• Spring (throttle valve) "3"
• Mixing chamber top "4"
• Throttle cable "5"
While compressing the spring (throt-
tle valve), disconnect the throttle ca-
ble.
CHECKING THE CARBURETOR
1. Inspect:
• Carburetor body
Contamination→Clean.
When cleaning the main air pas-
sage "a", do not blow air at the fil-
ter side because it will clog the
passage with mud or sand.
• Use a petroleum based solvent for
cleaning. Blow out all passages and
jets with compressed air.
• Never use a wire.
• When cleaning the main air pas-
sage, blow air through it while cov-
ering the nozzle with a clean rag.
2. Inspect:
•Main jet "1"
• Main jet holder "2"
• Pilot jet "3"
Contamination→Clean.
• Use a petroleum based solvent for
cleaning. Blow out all passages and
jets with compressed air.
• Never use a wire.
CHECKING THE NEEDLE VALVE
1. Inspect:
• Needle valve "1"
• Valve seat "2"
Grooved wear "a" →Replace.
Dust "b" →Clean.
Always replace the needle valve and
valve seat as a set.
CHECKING THE THROTTLE
VALVE
1. Check:
• Free movement
Stick→Repair or replace.
Insert the throttle valve "1" into the
carburetor body, and check for free
movement.
CHECKING THE JET NEEDLE
1. Inspect:
• Jet needle "1"
Bends/wear→Replace.
• Clip groove
Free play exists/wear→Replace.
• Clip position
CHECKING THE FILTER
1. Inspect:
•Filter "1"
Damage→Replace.
Inspect the filter as it is assembled to
the carburetor. Do not remove the fil-
ter except when replacing it.
MEASURING AND ADJUSTING
THE FUEL LEVEL
1. Measure:
• Fuel level "a"
Out of specification→Adjust.
Fuel level Measurement and ad-
justment steps:
a. Remove the drain plug.
b. Connect the fuel level gauge
adapter "2" and fuel level gauge
"1" to the float chamber.
c. Hold the fuel level gauge vertical-
ly next to the float chamber mat-
ing surface.
Standard clip position:
No.3 Groove
Fuel level:
9.5–10.5 mm (0.37–0.41
in)
Above the float cham-
ber mating surface
Fuel level gauge adapter:
YM-01470/90890-01470
Fuel level gauge:
YM-1312-A/90890-
01312

4-10
CARBURETOR AND REED VALVE
d. Measure the fuel level with the
fuel level gauge.
Keep the carburetor and fuel level
gauge vertically when measuring the
fuel level.
e. If the fuel level is not within speci-
fication, inspect the valve seat
and needle valve.
f. If either is worn, replace them
both.
g. If both are fine, adjust the fuel lev-
el by bending the float tab "b" on
the float.
h. Recheck the fuel level.
CHECKING THE FLOAT
1. Inspect:
• Float "1"
Damage→Replace.
CHECKING THE REED VALVE
1. Measure:
• Reed valve bending "a"
Out of specification→Replace.2. Measure:
• Valve stopper height "a"
Out of specification→Adjust stop-
per/Replace valve stopper.
INSTALLING THE REED VALVE
1. Install:
• Reed valve "1"
• Stopper (reed valve) "2"
• Screw (reed valve) "3"
• Install the reed valve with the reed
valve bending as shown.
• Note the cut "a" in the lower corner
of the reed and stopper plate.
Tighten each screw gradually to
avoid warping.
2. Install:
• Reed valve assembly "1"
• Reed valve spacer "2"
3. Install:
• Carburetor joint "1"
• Bolt (carburetor joint) "2"ASSEMBLING THE CARBURETOR
1. Install:
• Throttle stop screw "1"
• Locknut "2"
• Pilot air screw "3"
Note the following installation
points:
a. Screw in the pilot air screw until it
is lightly seated.
b. Back out it by the specified num-
ber of turns.
2. Install:
• Starter plunger "1"
3. Install:
• Main jet holder "1"
•Main jet "2"
• Pilot jet "3"
• Valve seat "4"
• Screw (valve seat) "5"
4. Install:
• Needle valve "1"
• Float "2"
• Float pin "3"
• Screw (float pin) "4"
• Needle jet cover "5" Reed valve bending limit:
0.2 mm (0.008 in)
Valve stopper height:
8.2–8.6 mm (0.323–
0.339 in)
Screw (reed valve):
1 Nm (0.1 m•kg, 0.7
ft•lb)
Bolt (carburetor joint):
10 Nm (1.0 m•kg, 7.2
ft•lb)
Pilot air screw:
2-1/4 turns out

4-11
CARBURETOR AND REED VALVE
• After installing the needle valve to
the float, install them to the carbure-
tor.
• Check the float for smooth move-
ment.
5. Install:
• Float chamber "1"
• Plate "2"
• Screw (float chamber) "3"
6. Install:
• Jet needle "1"
• Needle holder "2"
To throttle valve "3".
7. Install:
• Throttle cable "1"
• Locknut "2"
• Mixing chamber top "3"
• Spring (throttle valve) "4"
• Ring "5"
• Throttle valve "6"
• While compressing the spring, con-
nect the throttle cable.
• Align the projection "a" on the ring
with the groove "b" in the needle
holder "7".
8. Install:
• Mixing chamber top "1"
• Screw (mixing chamber top) "2"
To carburetor "3".
After installing, check the throttle grip
for smooth movement.
9. Install:
• Air vent hose "1"
• Overflow hose "2"
•Clamp "3"
Pass the air vent hose at the rear (on
the air cleaner side) of the throttle ca-
ble "4".
INSTALLING THE CARBURETOR
1. Install:
• Carburetor "1"
Install the projection between the car-
buretor joint slots.
2. Tighten:
• Bolt (air filter joint) "1"
• Bolt (carburetor joint) "2"
3. Clamp:
• Air vent hose "1"
• Overflow hose "2"
Refer to "CABLE ROUTING DIA-
GRAM" section in the CHAPTER
2.
4. Adjust:
• Idle speed
Refer to "ADJUSTING THE EN-
GINE IDLING SPEED" section in
the CHAPTER 3. Locknut:
4 Nm (0.4 m•kg, 2.9
ft•lb)
Bolt (air filter joint):
2 Nm (0.2 m•kg, 1.4
ft•lb)
Bolt (carburetor joint):
2 Nm (0.2 m•kg, 1.4
ft•lb)

4-12
CYLINDER HEAD, CYLINDER AND PISTON
CYLINDER HEAD, CYLINDER AND PISTON
REMOVING THE CYLINDER HEAD AND CYLINDER
Order Part name Q'ty Remarks
Seat and fuel tank Refer to "SEAT, FUEL TANK AND SIDE
COVERS" section.
Exhaust pipe and silencerRefer to "EXHAUST PIPE AND SILENCER"
section.
Radiator Refer to "RADIATOR" section.
1 Spark plug 1
2 Engine bracket 2
3 Nut (cylinder head) 5Loosen each nut 1/4 turn, and remove them
after all nuts are loosened.
4 Cylinder head 1
5 Power valve housing 1
6 Push rod 1 Refer to removal section.
7 Nut (cylinder) 4
8 Cylinder 1
5 Nm (0.5 m kg, 3.6 ft lb)
4 Nm (0.4 m kg, 2.9 ft lb)
13 Nm (1.3 m kg, 9.4 ft lb)
28 Nm (2.8 m kg, 20 ft lb)
20 Nm (2.0 m kg, 14 ft lb)
30 Nm (3.0 m kg, 22 ft lb)
34 Nm (3.4 m kg, 24 ft lb)