2008 YAMAHA WR 450F Owners Manual

5-9
CARBURETOR
e. If both are fine, adjust the float
height by bending the float tab "b"
on the float.
f. Recheck the float height.
CHECKING THE FLOAT
1. Inspect:
• Float "1"
Damage→Replace.
CHECKING THE STARTER
PLUNGER
1. Inspect:
• Cold starter plunger "1"
• Hot starter plunger "2"
Wear/damage→Replace.
CHECKING THE ACCELERATOR
PUMP
1. Inspect:
• Diaphragm (accelerator pump)
"1"
• Spring (accelerator pump) "2"
• Accelerator pump cover "3"
• O-ring "4"
• Push rod "5"
Tears (diaphragm)/damage→Re-
place.
Dirt→Clean.2. Inspect:
• Throttle shaft "1"
• Spring "2"
• Lever 1 "3"
• Spring 1 "4"
• Lever 2 "5"
• Spring 2 "6"
Dirt→Clean.
CHECKING THE AIR CUT VALVE
1. Inspect:
• Diaphragm (air cut valve) "1"
• Spring (air cut valve) "2"
• Air cut valve cover "3"
• O-ring "4"
Tears (diaphragm)/damage→Re-
place.
ASSEMBLING THE CARBURETOR
1. Install:
• Cold starter plunger
2. Install:
•Pilot air jet "1"
3. Install:
• Spring 1 "1"
• Lever 1 "2"
To lever 2 "3".
Make sure the spring 1 fits on the
stopper "a" of the lever 2.
4. Install:
• Spring 2 "1"
To lever 2 "2".
5. Install:
• Push rod link lever assembly "1"
Make sure the stopper "a" of the
spring 2 fits into the recess "b" in the
carburetor.
6. Install:
• Washer "1"
• Circlip "2"
7. Install:
• Spring "1"
To throttle shaft "2".
Install the bigger hook "a" of the
spring fits on the stopper "b" of the
throttle shaft pulley.
8. Install:
• Throttle shaft assembly "1"
• Washer (metal) "2"
• Washer (resin) "3"
• Valve lever "4"

5-10
CARBURETOR
• Apply the fluorochemical grease on
the bearings.
• Fit the projection "a" on the throttle
shaft assembly into the slot "b" in
the throttle position sensor.
• Make sure the stopper "c" of the
spring fits into the recess in the car-
buretor.
• Turn the throttle shaft assembly left
while holding down the lever 1 "5"
and fit the throttle stop screw tip "d"
to the stopper "e" of the throttle
shaft assembly pulley.
9. Install:
• Push rod "1"
While holding down the lever 1 "2", in-
sert the push rod farthest into the car-
buretor.
10. Install:
• Starter jet "1"
• Pilot jet "2"
• Spacer "3"
• Needle jet "4"
•Main jet "5"11. Install:
• Needle valve "1"
•Float "2"
• Float pin "3"
• After installing the needle valve to
the float, install them to the carbure-
tor.
• Check the float for smooth move-
ment.
12. Install:
• Pilot screw "1"
• Spring "2"
• Washer "3"
• O-ring "4"
Note the following installation
points:
a. Turn in the pilot screw until it is
lightly seated.
b. Turn out the pilot screw by the
number of turns recorded before
removing.
13. Install:
• O-ring
• Leak jet "1"
• Float chamber "2"
• Bolt (float chamber) "3"
• Cable holder (throttle stop screw
cable) "4"
• Hose holder (carburetor breather
hose) "5"14. Install:
• Diaphragm (air cut valve) "1"
• Spring (air cut valve) "2"
• O-ring "3"
• Air cut valve cover "4"
• Holder (cylinder head breather
hose) "5"
• Screw (air cut valve cover) "6"
15. Install:
• Diaphragm (accelerator pump)
"1"
• Spring "2"
• O-ring "3"
• Accelerator pump cover "4"
• Hose holder (drain hose) "5"
• Screw (accelerator pump cover)
"6"
Install the diaphragm (accelerator
pump) with its mark "a" facing the
spring.
16. Install:
• Jet needle "1"
•Collar "2"
• Spring "3"
• Needle holder "4"
• Throttle valve plate "5"
To throttle valve "6".
Pilot screw (example):
2 turns out

5-11
CARBURETOR
17. Install:
• Throttle valve assembly "1"
• Screw (throttle shaft) "2"
Install the valve lever rollers "3" into
the slits "a" of the throttle valve.
18. Install:
• O-ring "1"
• Valve lever housing cover "2"
• Bolt (valve lever housing cover)
"3"
19. Install:
• Carburetor breather hose "1"
Install the carburetor breather hoses
to the carburetor so that the hoses do
not bend near where they are in-
stalled.
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"
• Bracket (cylinder head breather
pipe) "2"
• Bolt (carburetor joint) "3"
• Cylinder head breather pipe "4"
• Cylinder head breather hose 1 "5"
• Cylinder head breather hose 2 "6"
• Cylinder head breather hose 3 "7"
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. Throttle valve height:
3.1 mm (0.122 in)
Bolt (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)

5-12
CARBURETOR
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.
9. Install:
• Clamp "1"
Refer to "CABLE ROUTING DIA-
GRAM" section in the CHAPTER
2.Bolt (throttle cable cov-
er):
4 Nm (0.4 m•kg, 2.9
ft•lb)

5-13
AIR INDICTOIN SYSTEM
AIR INDICTOIN SYSTEM
REMOVING THE AIR INDUCTION SYSTEM
Order Part name Q'ty Remarks
1 Bracket 1
2 Air cut-off valve assembly 1
3Air induction hose (air cut-off valve - front of cyl-
inder head)1
4 Air induction pipe 1
5 Gasket 1
6Air induction hose (air cut-off valve - rear of cylin-
der head)1
7Air induction hose (air cut-off valve - air filter
case)1

5-14
AIR INDICTOIN SYSTEM
CHECKING THE AIR INDUCTION
SYSTEM
1. Inspect:
• Air induction hose
Crack/damage→Replace.
• Air induction pipe
Crack/damage→Replace.
2. Check:
• Operation of air cut valve
Pass air through the pipe and
check the air cut valve for opera-
tion.
Does not meet the following con-
dition→Replace the air cut valve
assembly.
• Blow in air to check for operation.
• When using vacuum, check by the
use of the vacuum/pressure pump
gauge set "1".
When using vacuum on the pipe
"c", take care not to exceed the
specified value.
a. From air filter
b. To cylinder head (exhaust
port)
c. From cylinder head (intake
port)
A. Check for induction from air
filter.
B. Check for prevention of back-
flow into air filter.
C. Check for prevention of after-
burn. (When throttle is closed
at sudden deceleration) "a" to "b" Air passes.
"b" to "a" Air does not pass.
"a" to "b"Air does not pass
when specified pres-
sure is on "c".
Vacuum/pressure pump
gauge set:
YB-35956-A/90890-
06756
Vacuum specifying pres-
sure:
46.7–86.7 kPa (350–650
mmHg, 13.8–25.6 inHg)

5-15
CAMSHAFTS
CAMSHAFTS
REMOVING THE CYLINDER HEAD COVER
Order Part name Q'ty Remarks
Seat and fuel tank Refer to "REMOVING THE SEAT, FUEL
TANK AND SIDE COVERS" section in the
CHAPTER 3.
Air cut-off valve assembly Refer to "AIR INDUCTION SYSTEM" section.
Engine upper bracket (right) Refer to "ENGINE REMOVAL" section.
Engine upper bracket (left)
1 Spark plug 1
2 Cylinder head breather hose 1
3 Bolt (cylinder head cover) 2
4 Cylinder head cover 1
5 Cylinder head cover gasket 1

5-16
CAMSHAFTS
REMOVING THE CAMSHAFTS
Order Part name Q'ty Remarks
1 Timing mark accessing screw1 Refer to removal section.
2 Crankshaft end accessing screw 1 Refer to removal section.
3 Timing chain tensioner cap bolt 1 Refer to removal section.
4 Timing chain tensioner 1 Refer to removal section.
5 Gasket 1 Refer to removal section.
6 Bolt (camshaft cap) 10 Refer to removal section.
7 Camshaft cap 2 Refer to removal section.
8 Clip 2 Refer to removal section.
9 Exhaust camshaft 1 Refer to removal section.
10 Intake camshaft 1 Refer to removal section.