YAMAHA YZ125LC 2013 Owners Manual

7-6
CHASSIS
CHANGE OF THE HEAT RANGE
OF SPARK PLUGS
Judging from the discoloration of
spark plugs, if they are found improp-
er, it can be corrected by the following
two methods; changing carburetor
settings and changing the heat range
of spark plug.
• In principle, it is advisable to first
use spark plugs of standard heat
range, and judging from the discol-
oration of spark plugs, adjust carbu-
retor settings.
• If the calibration No. of the main jet
must be changed by ±30, it is advis-
able to change the heat range of
spark plugs and newly select the
proper main jet.
• When checking the discoloration of
spark plugs, be sure to stop the en-
gine immediately after a run and
check.
• Avoid racing.
• When changing the heat range of
spark plugs, never attempt to
change it more than ±1 rank.
• When using a spark plug other than
standard, check its heat range
against the standard and check that
it is a resistance type.
• Note that even if the discoloration
seems proper, it may slightly vary
with the spark plug maker and oil in
use.
CHASSIS
SELECTION OF THE SECONDARY
REDUCTION RATIO (SPROCKET) ondary gear reduction ratio>
• It is generally said that the second-
ary gear ratio should be reduced for
a longer straight portion of a speed
course and should be increased for
a course with many corners. Actual-
ly, however, as the speed depends
on the ground condition of the day
of the race, be sure to run through
the circuit to set the machine suit-
able for the entire course.
• In actuality, it is very difficult to
achieve settings suitable for the en-
tire course and some settings may
be sacrificed. Thus, the settings
should be matched to the portion of
the course that has the greatest ef-
fect on the race result. In such a
case, run through the entire course
while making notes of lap times to
find the best balance; then, deter-
mine the secondary reduction ratio.
• If a course has a long straight por-
tion where a machine can run at
maximum speed, the machine is
generally set such that it can devel-
op its maximum revolutions toward
the end of the straight line, with care
taken to avoid the engine over-rev-
ving.
Riding technique varies from rider to
rider and the performance of a ma-
chine also vary from machine to ma-
chine. Therefore, do not imitate other
rider's settings from the beginning but
choose your own setting according to
the level of your riding technique.
DRIVE AND REAR WHEEL
SPROCKETS SETTING PARTSTIRE PRESSURE
Tire pressure should be adjust to suit
the road surface condition of the cir-
cuit.
• Under a rainy, muddy, sandy, or
slippery condition, the tire pressure
should be lower for a larger area of
contact with the road surface.
• Under a stony or hard road condi-
tion, the tire pressure should be
higher to prevent a flat tire.
FRONT FORK SETTING
The front fork setting should be made
depending on the rider's feeling of an
actual run and the circuit conditions.
The front fork setting includes the fol-
lowing three factors:
1. Setting of air spring characteris-
tics
• Change the fork oil amount.
2. Setting of spring preload
• Change the spring.
3. Setting of damping force
• Change the compression damp-
ing.
• Change the rebound damping.
The spring acts on the load and
the damping force acts on the
cushion travel speed.
CHANGE IN AMOUNT AND
CHARACTERISTICS OF FORK OIL
Damping characteristic near the final
stroke can be changed by changing
the fork oil amount. Standard spark
plugBR9EVX/NGK
(resistance
type)
Secondary reduction ratio =
Number of rear wheel sprocket
teeth/Number of drive sprocket
teeth
Standard second-
ary reduction ratio3.692 (48/13)
Part name Size Part number
Drive
sprocket
"1"
(STD) 13T 9383B-13218
Rear wheel
sprocket
"2"
47T 1C3-25447-00
(STD) 48T 1C3-25448-00
49T 1C3-25449-00
50T 1C3-25450-00
51T 1C3-25451-00
52T 1C3-25452-00
Standard tire pressure:
100 kPa (1.0 kgf/cm2,
15 psi)
Extent of adjustment:
60–80 kPa (0.6–0.8
kgf/cm
2, 9.0–12 psi)
Extent of adjustment:
100–120 kPa (1.0–1.2
kgf/cm
2, 15–18 psi)

7-7
CHASSIS
Adjust the oil amount in 5 cm 3 (0.2
Imp oz, 0.2 US oz) increments or
decrements. Too small oil amount
causes the front fork to produce a
noise at full rebound or the rider to
feel some pressure on his hands
or body. Alternatively, too large oil
amount will cause the air spring
characteristics to have a tendency
to be stiffer with the consequent
deteriorated performance and
characteristics. Therefore, adjust
the front fork within the specified
range.
A. Air spring characteristics in
relation to oil amount change
B. Load
C. Stroke
1. Max. oil amount
2. Standard oil amount
3. Min. oil amount
SETTING OF SPRING AFTER
REPLACEMENT
As the front fork setting can be easily
affected by rear suspension, take
care so that the machine front and
rear are balanced (in position, etc.)
when setting the front fork.
1. Use of soft spring
• Change the rebound damping.
Turn out one or two clicks.
• Change the compression damp-
ing.
Turn in one or two clicks.
Generally a soft spring gives a soft
riding feeling. Rebound damping
tends to become stronger and the
front fork may sink deeply over a se-
ries of gaps.
2. Use of stiff spring
• Change the rebound damping.
Turn in one or two clicks.
• Change the compression damp-
ing.
Turn out one or two clicks.
Generally a stiff spring gives a stiff
riding feeling. Rebound damping
tends to become weaker, resulting in
lack of a sense of contact with the
road surface or in a vibrating handle-
bar.
FRONT FORK SETTING PARTS
• Front fork spring "1"
The I.D. mark (slits) "a" is proved on
the end of the spring.
REAR SUSPENSION SETTING
The rear suspension setting should
be made depending on the rider's
feeling of an actual run and the circuit
conditions.
The rear suspension setting includes
the following two factors:
1. Setting of spring preload
• Change the set length of the
spring.
• Change the spring.
2. Setting of damping force
• Change the rebound damping.
• Change the compression damp-
ing.
CHOOSING SET LENGTH
1. Place a stand or block under the
engine to put the rear wheel
above the floor, and measure the
length "a" between the rear wheel
axle center and the rear fender
holding bolt.
2. Remove the stand or block from
the engine and with a rider astride
the seat, measure the sunken
length "b" between the rear wheel
axle center and the rear fender
holding bolt.
3. Loosen the locknut "1" and make
adjustment by turning the spring
adjuster "2" to achieve the stan-
dard figure from the subtraction of
the length "b" from the length "a".
• If the machine is new and after it is
broken in, the same set length of
the spring may change because of
the initial fatigue, etc. of the spring.
Therefore, be sure to make reeval-
uation.
• If the standard figure cannot be
achieved by adjusting the spring
adjuster and changing the spring Standard oil amount:
333 cm
3 (11.72 Imp oz,
11.26 US oz)
*335 cm
3 (11.79 Imp oz,
11.33 US oz)
Extent of adjustment:
300–375 cm
3 (10.6–13.2
Imp oz, 10.1–12.7 US
oz)
* For EUROPE
TYPESPRI
NG
RATESPRING
PART
NUMBER
(-23141-)I.D.
MARK
(slits)
SOFT0.398 1C3-A1 |
0.408 1C3-B1 ||
STD 0.418 1C3-P0 —
STIFF0.428 1C3-D1 ||||
0.438 1C3-E1 |||||
0.449 1C3-F1 |-|
0.459 1C3-G1 |-||
0.469 1C3-H1 |-|||
0.479 1C3-J1 |-||||
Standard figure:
90–100 mm (3.5–3.9 in)

7-8
CHASSIS
set length, replace the spring with
an optional one and make readjust-
ment.
SETTING OF SPRING AFTER
REPLACEMENT
After replacement, be sure to adjust
the spring to the set length [sunken
length 90–100 mm (3.5–3.9 in)] and
set it.
1. Use of soft spring
• Set the soft spring for less re-
bound damping to compensate
for its less spring load. Run with
the rebound damping adjuster
one or two clicks on the softer
side and readjust it to suit your
preference.
2. Use of stiff spring
• Set the soft spring for more re-
bound damping to compensate
for its greater spring load. Run
with the rebound damping adjust-
er one or two clicks on the stiffer
side and readjust it to suit your
preference.
Adjusting the rebound damping will
be followed more or less by a change
in the compression damping. For cor-
rection, turn the low compression
damping adjuster on the softer side.
When using a rear shock absorber
other than currently installed, use
the one whose overall length "a"
does not exceed the standard as it
may result in faulty performance.
Never use one whose overall
length is greater than standard.
REAR SHOCK ABSORBER
SETTING PARTS
• Rear shock spring "1"
[Equal-pitch titanium spring]
[Equal-pitch steel spring]
[Unequal-pitch steel spring]
Install the spring seat "2" to the ti-
tanium spring.
• The unequal-pitch spring is softer in
initial characteristic than the equal-
pitch spring and is difficult to bottom
out under full compression.
• The I.D. mark "a" is marked at the
end of the spring.
• Spring specification varies accord-
ing to the color and quantity of I.D.
marks.
Length "a" of standard
shock:
490 mm (19.29 in)
TYPESPRI
NG
RATESPRING
PART
NUM-
B E R
(-22212-)I.D.
MARK
Green/1
SOFT 4.5 1C3-00 Green/2
Green/3
Red/1
STD 4.7 1C3-10 Red/2
Red/3
STIFF
Black/1
4.9 1C3-20 Black/2
Black/3
Blue/1
5.1 1C3-30 Blue/2
Blue/3
TYPESPRI
NG
RATESPRING
PART
NUM-
B E R
(-22212-)I.D.
MARK/
Q'TY
SOFT 4.3 5UN-00 Brown/1
5.3 5UN-50 Yellow/1
STIFF5.5 5UN-60 Pink/1
5.7 5UN-70 White/1
TYPESPRI
NG
RATE
(ap-
prox.)SPRING
PART
NUM-
B E R
(-22212-)I.D.
MARK/
Q'TY
SOFT 4.5 5UN-A0 Green/2
4.7 5UN-B0 Red/2
4.9 5UN-C0 Black/2
5.1 5UN-D0 Blue/2
STIFF
5.3 5UN-E0 Yellow/2
5.5 5UN-F0 Pink/2
5.7 5UN-G0 White/2

7-9
CHASSIS
• Extent of adjustment (spring pre-
load)
• For the spring preload adjustment,
refer to "ADJUSTING THE REAR
SHOCK ABSORBER SPRING
PRELOAD" in the CHAPTER 3.
• Preload adjusting extent is the
same for the titanium and steel
springs.
SPRING
PART
NUMBER
(-22212-)
Maximum Minimum
1C3-00
1C3-10
1C3-20
1C3-30
5UN-00
5UN-A0
5UN-B0
5UN-C0
5UN-D0
5UN-E0
5UN-F0
5UN-G0Position
in which
the spring
is turned
in 18 mm
(0.71 in)
from its
free
length.Position
in which
the spring
is turned
in 1.5 mm
(0.06 in)
from its
free
length. 5UN-50
5UN-60
5UN-70Position
in which
the spring
is turned
in 20 mm
(0.79 in)
from its
free
length.

7-10
CHASSIS
SUSPENSION SETTING (FRONT FORK)
• If any of the following symptoms is experienced with the standard position as the base, make resetting by reference to
the adjustment procedure given in the same chart.
• Before any change, set the rear shock absorber sunken length to the standard figure 90–100 mm (3.5–3.9 in).
SymptomSection
Check Adjust
JumpLarge
gapMedi-
um
gapSmall
gap
Stiff over entire
range○○○Compression damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Oil amount Decrease oil amount by about 5–10 cm
3
(0.2–0.4 Imp oz, 0.2–0.3 US oz).
Spring Replace with soft spring.
Unsmooth move-
ment over entire
range○○○○Outer tube Check for any bends, dents, and other noticeable
scars, etc. If any, replace affected parts.
Inner tube
Slide metal Replace with a new one for extended use.
Piston metal Replace with a new one for extended use.
Under bracket tighten-
ing torqueRetighten to specified torque.
Poor initial move-
ment○Rebound damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Oil seal Apply grease in oil seal wall.
Soft over entire
range, bottoming
out○○Compression damping Turn adjuster clockwise (about 2 clicks) to in-
crease damping.
Oil amount Increase oil amount by about 5–10 cm
3
(0.2–0.4 Imp oz, 0.2–0.3 US oz).
Spring Replace with stiff spring.
Stiff toward stroke
end○Oil amountDecrease oil amount by about 5 cm
3
(0.2 Imp oz,0.2 US oz).
Soft toward stroke
end, bottoming out○Oil amountIncrease oil amount by about 5 cm
3
(0.2 Imp oz,0.2 US oz).
Stiff initial move-
ment○○○○Compression dampingTurn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Low front, tending to
lower front posture○○Compression damping Turn adjuster clockwise (about 2 clicks) to in-
crease damping.
Rebound damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Balance with rear end Set sunken length for 95–100 mm (3.7–3.9 in)
when one passenger is astride seat
(lower rear posture).
Oil amount Increase oil amount by about 5 cm
3
(0.2 Imp oz, 0.2 US oz).
"Obtrusive" front,
tending to upper
front posture○○Compression damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Balance with rear end Set sunken length for 90–95 mm (3.5–3.7 in)
when one passenger is astride seat
(upper rear posture).
Spring Replace with soft spring.
Oil amount Decrease oil amount by about 5–10 cm
3
(0.2–0.4 Imp oz, 0.2–0.3 US oz).

7-11
CHASSIS
SUSPENSION SETTING (REAR SHOCK ABSORBER)
• If any of the following symptoms is experienced with the standard position as the base, make resetting by reference to
the adjustment procedure given in the same chart.
• Adjust the rebound damping in 2-click increments or decrements.
• Adjust the low compression damping in 1-click increments or decrements.
• Adjust the high compression damping in 1/6 turn increments or decrements.
SymptomSection
Check Adjust
JumpLarge
gapMedi-
um
gapSmall
gap
Stiff, tending to sink○○Rebound damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Spring set length Set sunken length for 90–100 mm (3.5–3.9 in)
when one passenger is astride seat.
Spongy and unsta-
ble○○Rebound damping Turn adjuster clockwise (about 2 clicks) to in-
crease damping.
Low compression
dampingTurn adjuster clockwise (about 1 click) to increase
damping.
Spring Replace with stiff spring.
Heavy and dragging○○Rebound damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Spring Replace with soft spring.
Poor road gripping○Rebound damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Low compression
dampingTurn adjuster clockwise (about 1 clicks) to in-
crease damping.
High compression
dampingTurn adjuster clockwise (about 1/6 turn) to in-
crease damping.
Spring set length Set sunken length for 90–100 mm (3.5–3.9 in)
when one passenger is astride seat.
Spring Replace with soft spring.
Bottoming out○○High compression
dampingTurn adjuster clockwise (about 1/6 turn) to in-
crease damping.
Spring set length Set sunken length for 90–100 mm (3.5–3.9 in)
when one passenger is astride seat.
Spring Replace with stiff spring.
Bouncing○○Rebound damping Turn adjuster clockwise (about 2 clicks) to in-
crease damping.
Spring Replace with soft spring.
Stiff travel○○High compression
dampingTurn adjuster counterclockwise (about 1/6 turn) to
decrease damping.
Spring set length Set sunken length for 90–100 mm (3.5–3.9 in)
when one passenger is astride seat.
Spring Replace with soft spring.

PR IN TE D IN J A PAN(E )PR IN TE D O N R EC YC LE D P APER