Yamaha 2003 YZ450F Service Manual

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INSP
ADJ
IDLE SPEED ADJUSTMENT/
VALVE CLEARANCE ADJUSTMENT
EC35M021
IDLE SPEED ADJUSTMENT
1. Start the engine and thoroughly warm it
up.
2. Adjust:
● Idle speed
Adjustment steps:
● Adjust the pilot screw.
Refer to “PILOT SCREW ADJUSTMENT”
section.
● Turn the throttle stop screw 1 until the
engine runs at the lowest possible speed.
To increase idle speed →
Turn the throttle stop screw 1 in a.
To decrease idle speed →
Turn the throttle stop screw 1 out b.
Engine idling speed:
1,900 ~ 2,100 r/min
VALVE CLEARANCE ADJUSTMENT
N
OTE:
● The valve clearance should be adjusted
when the engine is cool to the touch.
● The piston must be at Top Dead Center
(T.D.C.) on compression stroke to check or
adjust the valve clearance.
1. Remove:
● Seat
● Fuel tank
Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section in the CHAPTER 4.
2. Remove:
● Carburetor
Refer to “CARBURETOR” section in
the CHAPTER 4.
● Spark plug cap
● Engine stay (upper)
● Cylinder head cover
Refer to “CAMSHAFTS” section in the
CHAPTER 4.
3. Remove:
● Timing plug 1
● Straight plug 2
● O-ring

Yamaha 2003 YZ450F Specifications

General

Bore x Stroke	95.0mm x 63.4mm
Compression Ratio	12.5:1
Ignition	CDI
Transmission	5-speed
Final Drive	Chain
Front Tire	80/100-21
Rear Tire	110/90-19
Wheelbase	58.5 inches
Ground Clearance	14.6 inches
Front Suspension	48mm Kayaba inverted telescopic fork; fully adjustable, 11.8-in travel
Rear Suspension	Kayaba single shock; fully adjustable, 12.4-in travel
Front Brake	250mm disc
Rear Brake	245mm disc
Fuel Capacity	1.8 gal
Seat Height	39.1 inches
Width	32.5 inches
Height	51.4 inches
Dry Weight	220 lb
Engine Type	449cc liquid-cooled DOHC 4-stroke; 5 titanium valves