2003 YAMAHA WR 450F valve

4 - 12
ENGCARBURETOR
Needle valve
1. Inspect:
Needle valve 1
Valve seat 2
Grooved wear a → Replace.
Dust b → Clean.
EC464300
Throttle valve
1. Check:
Free movement
Stick → Repair or replace.
Insert the throttle valve 1 into the car-
buretor body, and check for free move-
ment.
EC464400
Jet needle
1. Inspect:
Jet needle 1
Bends/wear → Replace.
Clip groove
Free play exists/wear → Replace.
Clip position
Standard clip position:
No.4 Groove
EC464511
Float height
1. Measure:
Float height a
Out of specification → Adjust.
Float height:
8.0 mm (0.31 in)

4 - 13
ENGCARBURETOR
Measurement and adjustment steps:
Hold the carburetor in an upside down
position.
NOTE:
Slowly tilt the carburetor in the opposite
direction, then take the measurement
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, result-
ing in an incorrect measurement.
Measure the distance between the mating
surface of the float chamber and top of the
float using a vernier calipers.
NOTE:
The float arm should be resting on the nee-
dle valve, but not compressing the needle
valve.
If the float height is not within specifica-
tion, inspect the valve seat and needle
valve.
If either is worn, replace them both.
If both are fine, adjust the float height by
bending the float tab b on the float.
Recheck the float height.
EC464600
Float
1. Inspect:
Float 1
Damage → Replace.
Starter plunger
1. Inspect:
Cold starter plunger 1
Hot starter plunger 2
Wear/damage → Replace.

4 - 14
ENG
Accelerator pump
1. Inspect:
Diaphragm (accelerator pump) 1
Spring 2
Cover 3
O-ring 4
Push rod 5
Tears (diaphragm)/damage → Replace.
Dirt → Clean.
2. Inspect:
Throttle shaft 1
Spring 2
Lever 1 3
Spring 1 4
Lever 2 5
Spring 2 6
Dirt → Clean.
12
3456
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 → Replace.
1
23
4
ASSEMBLY AND INSTALLATION
Carburetor
1. Install:
Cold starter plunger 1
2. Install:
Pilot air jet 1
1
CARBURETOR

4 - 16
ENGCARBURETOR
8. Install:
Throttle shaft assembly 1
Plain washer (metal) 2
Plain washer (resin) 3
Valve lever 4
NOTE:
Apply the fluorochemical grease on the bear-
ings.
Fit the projection a on the throttle shaft
assembly into the slot b in the TPS (throttle
position sensor).
Make sure the stopper c of the spring fits
into the recess in the carburetor.
Turn the throttle shaft assembly left while
holding down the lever 1 5 and fit the throt-
tle stop screw tip d to the stopper e of the
throttle shaft assembly pulley.
1
23
4
b
a
c
e
d
5
9. Install:
Push rod 1
NOTE:
While holding down the lever 1 2, insert the
push rod farthest into the carburetor.12
10. Install:
Starter jet 1
Pilot jet 2
Spacer 3
Needle jet 4
Main jet 5

4 - 17
ENGCARBURETOR
11. Install:
Needle valve 1
Float 2
Float pin 3
NOTE:
After installing the needle valve to the float,
install them to the carburetor.
Check the float for smooth movement.
12. Install:
Pilot screw 1
Spring 2
Washer 3
O-ring 4
* Except for USANote the following installation points:
Turn in the pilot screw until it is lightly
seated.
Turn out the pilot screw by the number of
turns recorded before removing.
Pilot screw:
1-3/4 turns out (example)
*1-1/2 turns out (example)
13. Install:
O-ring
Leak jet 1
Float chamber 2
Screw (float chamber) 3
Cable holder (throttle stop screw cable)
4
Hose holder (carburetor breather hose)
5
532 4
5
1
14. Install:
Diaphragm (air cut valve) 1
Spring (air cut valve) 2
O-ring 3
Air cut valve cover 4
Screw (air cut valve cover) 5
1
2
3
5
4

4 - 18
ENGCARBURETOR
15. Install:
Diaphragm (accelerator pump) 1
Spring 2
O-ring 3
Cover 4
Hose holder (drain hose) 5
Screw (cover) 6
NOTE:
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.
5
6
1
2
3
4
17. Install:
Throttle valve assembly 1
Screw (throttle shaft) 2
NOTE:
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
Refer to “CABLE ROUTING DIA-
GRAM” section in the CHAPTER 2.

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ENGCARBURETOR
Accelerator pump timing adjustment
Adjustment steps:
NOTE:
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 diameter as the specified
value.
Throttle valve height:
3.1 mm (0.122 in)
Fully turn in the accelerator pump adjust-
ing screw 3.
Check that the link lever 4 has free play
b by pushing lightly on it.
Gradually turn out the adjusting screw
while moving the link lever until it has no
more free play.
Carburetor installation
1. Install:
Carburetor joint 1
NOTE:
Install the projection a on the cylinder head
between the carburetor joint slots b.
T R..3 Nm (0.3 m · kg, 2.2 ft · lb)
2. Install:
Carburetor 1
NOTE:
Install the projection a between the carburetor
joint slots.
3. Install:
Hot starter plunger 1
1
T R..2 Nm (0.2 m · kg, 1.4 ft · lb)

4 - 27
ENGCAMSHAFTS
Fit the timing chain 3 onto both camshaft
sprockets and install the camshafts on the
cylinder head.
NOTE:
The camshafts should be installed onto the
cylinder head so that the exhaust cam
sprocket punch mark c and the intake cam
sprocket punch mark d align with the sur-
face of the cylinder head.
CAUTION:
Do not turn the crankshaft during the
camshaft installation. Damage or
improper valve timing will result.
Install the clips and camshaft caps 4.
T R..
Bolt (camshaft cap):
10 Nm (1.0 m • kg, 7.2 ft • lb)
NOTE:
Apply the engine oil on the thread and con-
tact surface of the bolts (camshaft cap) 5.
Tighten the bolts (camshaft cap) in a criss-
cross pattern.
CAUTION:
The bolts (camshaft cap) must be tight-
ened evenly, or damage to the cylinder
head, camshaft caps, and camshaft will
result.
5
4
E
2. Install:
Timing chain tensioner
Installation steps:
While pressing the tensioner rod lightly
with fingers, use a thin screwdriver and
wind the tensioner rod up fully clockwise.