height adjustment YAMAHA YZ450F 2009 Owners Manual

3-14
CHASSIS
CHASSIS
BLEEDING THE HYDRAULIC
BRAKE SYSTEM
Bleed the brake system if:
• The system has been disassem-
bled.
• A brake hose has been loosened
or removed.
• The brake fluid is very low.
• The brake operation is faulty.
A dangerous loss of braking per-
formance may occur if the brake
system is not properly bled.
1. Remove:
• Brake master cylinder cap
• Diaphragm
• Reservoir float (front brake)
• Protector (rear brake)
2. Bleed:
• Brake fluid
Air bleeding steps:
a. Add proper brake fluid to the res-
ervoir.
b. Install the diaphragm. Be careful
not to spill any fluid or allow the
reservoir to overflow.
c. Connect the clear plastic tube "2"
tightly to the caliper bleed screw
"1".
A. Front
B. Rear
d. Place the other end of the tube
into a container.
e. Slowly apply the brake lever or
pedal several times.
f. Pull the lever in or push down on
the pedal. Hold the lever or pedal
in position.
g. Loosen the bleed screw and allow
the lever or pedal to travel to-
wards its limit.h. Tighten the bleed screw when the
lever or pedal limit has been
reached; then release the lever or
pedal.
i. Repeat steps (e) to (h) until of the
air bubbles have been removed
from the system.
If bleeding is difficult, it may be nec-
essary to let the brake fluid system
stabilize for a few hours. Repeat the
bleeding procedure when the tiny
bubbles in the system have disap-
peared.
j. Add brake fluid to the level line on
the reservoir.
Check the operation of the brake
after bleeding the brake system.
3. Install:
• Protector (rear brake)
• Reservoir float (front brake)
• Diaphragm
• Brake master cylinder cap
ADJUSTING THE FRONT BRAKE
1. Check:
• Brake lever position "a"
2. Remove:
• Brake lever cover
3. Adjust:
• Brake lever position
Brake lever position adjustment
steps:
a. Loosen the locknut "1".
b. Turn the adjusting bolt "2" until the
lever position "a" is within speci-
fied position.c. Tighten the locknut.
Be sure to tighten the locknut, as it
will cause poor brake perfor-
mance.
4. Install:
• Brake lever cover
ADJUSTING THE REAR BRAKE
1. Check:
• Brake pedal height "a"
Out of specification→Adjust.
2. Adjust:
• Brake pedal height
Pedal height adjustment steps:
a. Loosen the locknut "1".
b. Turn the adjusting nut "2" until the
pedal height "a" is within specified
height.
c. Tighten the locknut.
• Adjust the pedal height between
the maximum "A" and the mini-
mum "B" as shown. (In this ad-
justment, the bolt "3" end "b"
should protrude out of the
threaded portion "4" but not be
less than 2 mm (0.08 in) "c" away
from the brake pedal "5").
• After the pedal height adjust-
ment, make sure that the rear
brake does not drag.
Bleed screw:
6 Nm (0.6 m•kg, 4.3
ft•lb)
Brake lever position "a":
Standard posi-
tionExtent of ad-
justment
95 mm (3.74 in)86–105 mm
(3.39–4.13 in)
Locknut:
5 Nm (0.5 m •kg, 3.6
ft•lb)
Brake pedal height "a":
5 mm (0.20 in)

4-10
CARBURETOR
HANDLING NOTE
Do not loosen the screw (throttle
position sensor) "1" except when
changing the throttle position sen-
sor due to failure because it will
cause a drop in engine perfor-
mance.
REMOVING THE PILOT SCREW
1. Remove:
• Pilot screw "1"
To optimize the fuel flow at a small
throttle opening, each machine's pilot
screw has been individually set at the
factory. Before removing the pilot
screw, turn it in fully and count the
number of turns. Record this number
as the factory-set number of turns
out.
CHECKING THE CARBURETOR
1. Inspect:
• Carburetor body
Contamination→Clean.
• Use a petroleum based solvent for
cleaning. Blow out all passages and
jets with compressed air.
• Never use a wire.
2. Inspect:
•Main jet "1"
• Pilot jet "2"
• Needle jet "3"
• Starter jet "4"
• Pilot air jet "5"•Leak jet "6"
Damage→Replace.
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.
•Filter "c"
Clogged→Clean.
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 positionMEASURING AND ADJUSTING
THE FLOAT HEIGHT
1. Measure:
• Float height "a"
Out of specification→Adjust.
Measurement and adjustment
steps:
a. Hold the carburetor in an upside
down position.
• Slowly tilt the carburetor in the op-
posite direction, then take the mea-
surement when the needle valve
aligns with the float arm.
• If the carburetor is level, the weight
of the float will push in the needle
valve, resulting in an incorrect mea-
surement.
b. Measure the distance between
the mating surface of the float
chamber and top of the float using
a vernier calipers.
The float arm should be resting on the
needle valve, but not compressing
the needle valve.
c. If the float height is not within
specification, inspect the valve
seat and needle valve.
d. If either is worn, replace them
both.
e. If both are fine, adjust the float
height by bending the float tab "b"
on the float.
Standard clip position:
No.3 Groove
Float height:
8.0 mm (0.31 in)

4-13
CARBURETOR
ADJUSTING THE ACCELERATOR
PUMP TIMING
Adjustment steps:
In order for the throttle valve height
"a" to achieve the specified value,
tuck under the throttle valve plate "1"
the rod "2" etc. with the same outer di-
ameter as the specified value.
a. Fully turn in the accelerator pump
adjusting screw "3".
b. Check that the link lever "4" has
free play "b" by pushing lightly on
it.
c. Gradually turn out the adjusting
screw while moving the link lever
until it has no more free play.
INSTALLING THE CARBURETOR
1. Install:
• Carburetor joint "1"2. Install:
• Carburetor "1"
Install the projection "a" between the
carburetor joint slots.
3. Install:
• Hot starter plunger "1"
4. Tighten:
• Bolt (carburetor joint) "1"
• Bolt (air filter joint) "2"
5. Install:
• Throttle cable (pull) "1"
• Throttle cable (return) "2"6. Adjust:
• Throttle grip free play
Refer to "ADJUSTING THE
THROTTLE CABLE FREE PLAY"
section in the CHAPTER 3.
7. Install:
• Throttle cable cover "1"
• Bolt (throttle cable cover) "2"
8. Install:
• Throttle position sensor lead cou-
pler "1"
•Clamp "2"
Refer to "CABLE ROUTING DIA-
GRAM" section in the CHAPTER
2. Throttle valve height:
1.25 mm (0.049 in)
Carburetor joint:
10 Nm (1.0 m•kg, 7.2
ft•lb)
Hot starter plunger:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Bolt (carburetor joint):
3 Nm (0.3 m•kg, 2.2
ft•lb)
Bolt (air filter joint):
3 Nm (0.3 m•kg, 2.2
ft•lb)
Throttle cable (pull):
4 Nm (0.4 m•kg, 2.9
ft•lb)
Throttle cable (return):
11 Nm (1.1 m•kg, 8.0
ft•lb)Bolt (throttle cable cov-
er):
4 Nm (0.4 m•kg, 2.9
ft•lb)