CARB YAMAHA YZ250F 2009 User Guide

2-19
CABLE ROUTING DIAGRAM
F. Pass the clutch cable in front of
the radiator mounting boss.
G. Pass the fuel hose on the out-
side of throttle position sensor
lead.
H. Pass the carburetor breater hos-
es so that they are not pinched
between the upper engine
bracket and carburetor.
I. Pass the carburetor breather
hoses and overflow hose so that
all there hoses do not contact
the rear shock absorber.

3-1
MAINTENANCE INTERVALS
REGULAR INSPECTION AND ADJUSTMENTS
MAINTENANCE INTERVALS
The following schedule is intended as a general guide to maintenance and lubrication. Bear in mind that such factors as
weather, terrain, geographical location, and individual usage will alter the required maintenance and lubrication intervals. If
you are a doubt as to what intervals to follow in maintaining and lubricating your machine, consult your Yamaha dealer.
ItemAfter
break-
inEvery
race
Every
third
(or 500
km)Every
fifth (or
1,000
km)
As re-
quiredRemarks
ENGINE OIL
Replace●●
Inspect●●
OIL FILTER ELEMENT, OIL
STRAINER
Clean●
VALVES
Check the valve clearances●●The engine must be cold.
Inspect●Check the valve seats and valve
stems for wear.
Replace●
VALVE SPRINGS
Inspect●Check the free length and the tilt.
Replace●
VALVE LIFTERS
Inspect●Check for scratches and wear.
Replace●
CAMSHAFTS Inspect the camshaft surface.
Inspect●Inspect the decompression system.
Replace●
TIMING CHAIN SPROCKETS,
TIMING CHAIN
Inspect●Check for wear on the teeth and for
damage.
Replace●
PISTON
Inspect●●Inspect crack.
Clean●Inspect carbon deposits and eliminate
them.
Replace●
PISTON RING
Inspect●Check ring end gap.
Replace●●
PISTON PIN
Inspect●
Replace●
CYLINDER HEAD Inspect carbon deposits and eliminate
them.
Inspect and clean●Change gasket.
3

3-2
MAINTENANCE INTERVALS
CYLINDER
Inspect and clean●Inspect score marks.
Replace●Inspect wear.
CLUTCH
Inspect and adjust●●Inspect housing, friction plate, clutch
plate and spring.
Replace●
TRANSMISSION
Inspect●
Replace bearing●
SHIFT FORK, SHIFT CAM,
GUIDE BAR
Inspect●Inspect wear.
ROTOR NUT
Retighten●●
EXHAUST PIPE, SILENCER,
PROTECTOR
Inspect and retighten●●
Clean●
Replace●* Whichever comes first
CRANK
Inspect and clean●●
CARBURETOR
Inspect, adjust and clean●●
SPARK PLUG
Inspect and clean●●
Replace●
DRIVE CHAIN Use chain lube.
Lubricate, slack, alignment●●Chain slack: 50–60 mm (2.0–2.4 in)
Replace●
COOLING SYSTEM
Check coolant level and leakage●●
Check radiator cap operation●
Replace coolant●Every two years
Inspect hoses●
OUTSIDE NUTS AND BOLTS
Retighten●●Refer to "STARTING AND BREAK-
IN" section in the CHAPTER 1.
AIR FILTER
Clean and lubricate●●Use foam air-filter oil or equivalent oil.
Replace●
OIL FILTER
Replace●● ItemAfter
break-
inEvery
race
Every
third
(or 500
km)Every
fifth (or
1,000
km)
As re-
quiredRemarks

3-4
MAINTENANCE INTERVALS
STEERING HEAD
Inspect free play and retighten●●
Clean and lube●Lithium base grease
Replace bearing●
TIRE, WHEELS
Inspect air pressure, wheel run-
out, tire wear and spoke loose-
ness●●
Retighten sprocket bolt●●
Inspect bearings●
Replace bearings●
Lubricate●Lithium base grease
THROTTLE, CONTROL CABLE
Check routing and connection●●
Lubricate●●Yamaha cable lube or SAE 10W-30
motor oil
Inspect and clean (throttle ca-
ble)●●Inspect dirt and wear on the throttle
cable on the carburetor side.
HOT STARTER, CLUTCH LEVER
Inspect free play● ItemAfter
break-
inEvery
race
Every
third
(or 500
km)Every
fifth (or
1,000
km)
As re-
quiredRemarks

3-24
ELECTRICAL
ELECTRICAL
CHECKING THE SPARK PLUG
1. Remove:
• Spark plug
2. Inspect:
• Electrode "1"
Wear/damage→Replace.
• Insulator color "2"
Normal condition is a medium to
light tan color.
Distinctly different color→Check
the engine condition.
When the engine runs for many hours
at low speeds, the spark plug insula-
tor will become sooty, even if the en-
gine and carburetor are in good
operating condition.
3. Measure:
• Plug gap "a"
Use a wire gauge or thickness
gauge.
Out of specification→Regap.
4. Clean the plug with a spark plug
cleaner if necessary.
5. Tighten:
• Spark plug
• Before installing a spark plug, clean
the gasket surface and plug sur-
face.
• Finger-tighten "a" the spark plug
before torquing to specification "b".
CHECKING THE IGNITION TIMING
1. Remove:
• Timing mark accessing screw "1"
2. Attach:
• Timing light
• Digital tachometer
To the ignition coil lead (orange
lead"1").
3. Adjust:
• Engine idling speed
Refer to "ADJUSTING THE EN-
GINE IDLING SPEED" section.
4. Check:
• Ignition timing
Visually check the stationary
pointer "a" is within the firing
range "b" on the rotor.
Incorrect firing range→Check ro-
tor and pickup assembly.
5. Install:
• Timing mark accessing screw Spark plug gap:
0.7–0.8 mm (0.028–
0.031 in)
Spark plug:
13 Nm (1.3 m•kg, 9.4
ft•lb)
Timing light:
YM-33277-A/90890-
03141

4-7
CARBURETOR
CARBURETOR
REMOVING THE CARBURETOR
Order Part name Q'ty Remarks
Seat and fuel tank Refer to "SEAT, FUEL TANK AND SIDE
COVERS" section.
Rear shock absorber Refer to "REAR SHOCK ABSORBER" sec-
tion in the CHAPTER 5.
1Clamp 1
2 Throttle position sensor lead coupler 1
3 Throttle cable cover 1
4 Throttle cable 2
5 Clamp (air filter joint) 1 Loosen the screw (air filter joint).
6 Clamp (carburetor joint) 1 Loosen the screws (carburetor joint).
7 Hot starter plunger 1
8 Carburetor assembly 1
9 Carburetor joint 1
4 Nm (0.4 m kg, 2.9 ft lb)
4 Nm (0.4 m kg, 2.9 ft lb)
2 Nm (0.2 m kg, 1.4 ft lb)
3 Nm (0.3 m kg, 2.2 ft lb)
3 Nm (0.3 m kg, 2.2 ft lb)
11 Nm (1.1 m kg, 8.0 ft lb)
10 Nm (1.0 m kg, 7.2 ft lb)

4-8
CARBURETOR
DISASSEMBLING THE CARBURETOR
Order Part name Q'ty Remarks
1 Carburetor breather hose 4
2 Valve lever housing cover 1
3 Screw (throttle shaft) 1
4 Throttle valve 1
5 Needle holder 1
6 Jet needle 1
7 Accelerator pump cover 1
8Spring 1
9 Diaphragm (accelerator pump) 1
10 Float chamber 1
11 Leak jet 1
12 Pilot screw 1 Refer to removal section.
13 Float pin 1
14 Float 1
15 Needle valve 1
16 Main jet 1
17 Needle jet 1
18 Spacer 1

4-9
CARBURETOR
19 Pilot jet 1
20 Starter jet 1
21 Push rod 1 Pull the push rod.
22 Throttle shaft assembly 1
23 Push rod link lever assembly 1
24 Pilot air jet 1
25 Cold starter plunger 1 Order Part name Q'ty Remarks

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.4 Groove
* No.5 Groove
* Except for USA and CDN
Float height:
8.0 mm (0.31 in)

4-11
CARBURETOR
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.
ASSEMBLING THE CARBURETOR
1. Install:
• Cold starter plunger "1"
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"
• 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.