2005 YAMAHA YZ250F carburetor

6. GASOLINE CAN CAUSE INJURY.
If you should swallow some gasoline,
inhale excess gasoline vapors, or
allow any gasoline to get into your
eyes, contact a doctor immediately. If
any gasoline spills onto your skin or
clothing, immediately wash skin
areas with soap and water, and
change your clothes.
7. ONLY OPERATE THE MACHINE IN AN
AREA WITH ADEQUATE VENTILA-
TION.
Never start the engine or let it run for
any length of time in an enclosed
area. Exhaust fumes are poisonous.
These fumes contain carbon monox-
ide, which by itself is odorless and
colorless. Carbon monoxide is a dan-
gerous gas which can cause uncon-
sciousness or can be lethal.
8. PARK THE MACHINE CAREFULLY;
TURN OFF THE ENGINE.
Always turn off the engine if you are
going to leave the machine. Do not
park the machine on a slope or soft
ground as it may fall over.
9. THE ENGINE, EXHAUST PIPE, MUF-
FLER, AND OIL TANK WILL BE VERY
HOT AFTER THE ENGINE HAS BEEN
RUN.
Be careful not to touch them or to
allow any clothing item to contact
them during inspection or repair.
10. PROPERLY SECURE THE MACHINE
BEFORE TRANSPORTING IT.
When transporting the machine in
another vehicle, always be sure it is
properly secured and in an upright
position and that the fuel cock is in
the “OFF” position. Otherwise, fuel
may leak out of the carburetor or fuel
tank.

CHAPTER 4
ENGINE
SEAT, FUEL TANK
AND SIDE COVERS ..................................4-1
EXHAUST PIPE AND SILENCER .............4-3
RADIATOR ................................................4-5
CARBURETOR ..........................................4-8
CAMSHAFTS ...........................................4-21
CYLINDER HEAD ....................................4-30
VALVES AND VALVE SPRINGS ............4-33
CYLINDER AND PISTON ........................4-42
CLUTCH ...................................................4-49
OIL FILTER ELEMENT, WATER PUMP
AND RIGHT CRANKCASE COVER .......4-56
BALANCER .............................................4-63
OIL PUMP ................................................4-66
KICK SHAFT AND SHIFT SHAFT ..........4-71
CDI MAGNETO ........................................4-78
ENGINE REMOVAL .................................4-82
CRANKCASE AND CRANKSHAFT ........4-87
TRANSMISSION, SHIFT CAM
AND SHIFT FORK ...................................4-96
CHAPTER 5
CHASSIS
FRONT WHEEL AND REAR WHEEL .......5-1
FRONT BRAKE AND REAR BRAKE .....5-10
FRONT FORK ..........................................5-26
HANDLEBAR ...........................................5-42
STEERING ...............................................5-48
SWINGARM .............................................5-53
REAR SHOCK ABSORBER ....................5-61

1 - 11
GEN
INFO
CONTROL FUNCTIONS
EC156000
FRONT BRAKE LEVER
The front brake lever 1 is located on the right
handlebar. Pull it toward the handlebar to acti-
vate the front brake.
EC157000
REAR BRAKE PEDAL
The rear brake pedal 1 is located on the right
side of the machine. Press down on the brake
pedal to activate the rear brake.
EC158001
FUEL COCK
The fuel cock supplies fuel from the tank to
carburetor while filtering the fuel. The fuel cock
has the two positions:
OFF: With the lever in this position, fuel will not
flow. Always return the lever to this posi-
tion when the engine is not running.
ON: With the lever in this position, fuel flows
to the carburetor. Normal riding is done
with the lever in this position.
COLD STARTER KNOB
When cold, the engine requires a richer air-fuel
mixture for starting. A separate starter circuit,
which is controlled by the cold starter knob 1,
supplies this mixture. Pull the cold starter knob
out to open the circuit for starting. When the
engine has warmed up, push it in to close the
circuit.
HOT STARTER LEVER
The hot starter lever 1 is used when starting a
warm engine.
Use the hot starter lever when starting the
engine again immediately after it was stopped
(the engine is still warm). Pulling the hot starter
lever injects secondary air to thin the air-fuel
mixture temporarily, allowing the engine to be
started more easily.

1 - 14
GEN
INFO
STARTING AND BREAK-IN
WARNING
Never start or run the engine in a closed
area. The exhaust fumes are poisonous;
they can cause loss of consciousness and
death in a very short time. Always operate
the machine in a well-ventilated area.
CAUTION:
The carburetor on this machine has a
built-in accelerator pump. Therefore,
when starting the engine, do not operate
the throttle or the spark plug will foul.
Unlike a two-stroke engine, this engine
cannot be kick started when the throttle is
open because the kick starter may kick
back. Also, if the throttle is open the air/
fuel mixture may be too lean for the
engine to start.
Before starting the machine, perform the
checks in the pre-operation check list.
STARTING A COLD ENGINE
1. Inspect the coolant level.
2. Turn the fuel cock to “ON”.
3. Shift the transmission into neutral.
4. Fully open the cold starter knob 1.
5. Kick the kickstarter crank.
WARNING
Do not open the throttle while kicking the
kickstarter crank. Otherwise, the kick-
starter may kick back.
STARTING AND BREAK-IN

SPEC
2 - 2 Oil type or grade:
Engine oil (For USA and CDN)
At 5 °C (40 °F) or higher È
Yamalube 4 (20W-40) or SAE 20W-40 type
SG motor oil
(Non-Friction modified)
At 15 °C (60 °F) or lower É
Yamalube 4 (10W-30) or SAE 10W-30 type
SG motor oil
(Non-Friction modified)
and/or
Yamalube 4-R (15W-50)
(Non-Friction modified)
(Except for USA and CDN)
API “SG” or higher grade
Oil capacity:
Engine oil
Periodic oil change 1.0 L (0.88 Imp qt, 1.06 US qt)
With oil filter replacement 1.1 L (0.97 Imp qt, 1.16 US qt)
Total amount 1.2 L (1.06 Imp qt, 1.27 US qt)
Coolant capacity (including all routes): 0.9 L (0.79 Imp qt, 0.95 US qt)
Air filter: Wet type element
Fuel:
Type Premium unleaded gasoline only with a
research octane number of 95 or higher.
Tank capacity 7.0 L (1.54 Imp gal, 1.85 US gal)
Carburetor:
Type FCR-MX37
Manufacturer KEIHIN
Spark plug:
Type/manufacturer CR8E/NGK (resistance type)
Gap 0.7 ~ 0.8 mm (0.028 ~ 0.031 in)
Clutch type: Wet, multiple-disc
-20
-4-10
140
3010
5020
6830
8640 50
104
122 ˚CTemp.
˚F
10W-30
10W-40
20W-40
20W-50
15W-40
GENERAL SPECIFICATIONS

2

SPEC
2 - 8 Clutch plate thickness 1.1 ~ 1.3 mm (0.043 ~ 0.051 in) ----
Quantity 8 ----
Warp limit ---- 0.1 mm
(0.004 in)
Clutch spring free length 40.4 mm (1.59 in) 39.4 mm
(1.55 in)
Quantity 5 ----
Clutch housing thrust clearance 0.10 ~ 0.35 mm
(0.0039 ~ 0.0138 in)----
Clutch housing radial clearance 0.010 ~ 0.044 mm
(0.0004 ~ 0.0017 in)----
Clutch release method Inner push, cam push ----
Shifter:
Shifter type Cam drum and guide bar ----
Guide bar bending limit ---- 0.05 mm
(0.002 in)
Kickstarter:
Type Kick and ratchet type ----
Carburetor:
USAEUROPE, CDN,
ZA, AUS, NZ
Type/manufacturer FCR-MX37/
KEIHIN
←----
I. D. mark 5XC5 50 5XC6 60 ----
Main jet (M.J) #182
←----
Main air jet (M.A.J)ø2.0
←----
Jet needle – clip position (J.N) OBELR-4 OBEKS-4 ----
Cutaway (C.A) 1.5
←----
Pilot jet (P.J) #42
←----
Pilot air jet (P.A.J) #100
←----
Pilot outlet (P.O)ø0.9
←----
Pilot screw (example) (P.S) 1-7/8 2-1/8 ----
Bypass (B.P)ø1.0
←----
Valve seat size (V.S)ø3.8
←----
Starter jet (G.S) #72
←----
Leak jet (Acc.P) #90 #95 ----
Float height (F.H) 8 mm (0.31 in)
←----
Engine idle speed 1,900 ~
2,100 r/min
←----
Intake vacuum
29.3 ~ 34.7 kPa
(220 ~ 260 mmHg,
8.66 ~ 9.45 inHg)←----
Hot starter lever free play 3 ~ 6 mm
(0.12 ~ 0.24 in)
←---- Item Standard Limit
MAINTENANCE SPECIFICATIONS

SPEC
2 - 10 Part to be tightened Thread size Q’tyTightening torque
Nm m·kg ft·lb
Spark plug M10S × 1.0 1 13 1.3 9.4
Camshaft cap M6 × 1.0 10 10 1.0 7.2
Cylinder head blind plug screw M12 × 1.0 1 28 2.8 20
Cylinder head (stud bolt) M6 × 1.0 2 7 0.7 5.1
(stud bolt) M8 × 1.25 1 15 1.5 11
(bolt) M9 × 1.25 4 38 3.8 27
(nut) M6 × 1.0 2 10 1.0 7.2
Cylinder head cover M6 × 1.0 2 10 1.0 7.2
Cylinder M6 × 1.0 1 10 1.0 7.2
Balancer weight M6 × 1.0 2 10 1.0 7.2
Balancer shaft driven gear M14 × 1.0 1 50 5.0 36
Timing chain guide (intake side) M6 × 1.0 2 10 1.0 7.2
Timing chain tensioner M6 × 1.0 2 10 1.0 7.2
Timing chain tensioner cap bolt M6 × 1.0 1 7 0.7 5.1
Impeller M8 × 1.25 1 14 1.4 10
Radiator hose clamp M6 × 1.0 8 2 0.2 1.4
Coolant drain bolt M6 × 1.0 1 10 1.0 7.2
Water pump housing M6 × 1.0 4 10 1.0 7.2
Radiator M6 × 1.0 6 10 1.0 7.2
Radiator guard M6 × 1.0 2 10 1.0 7.2
Radiator pipe M6 × 1.0 1 10 1.0 7.2
Oil pump cover M4 × 0.7 1 2 0.2 1.4
Oil pump M6 × 1.0 3 10 1.0 7.2
Oil filter element drain bolt M6 × 1.0 1 10 1.0 7.2
Oil filter element cover M6 × 1.0 2 10 1.0 7.2
Oil strainer M6 × 1.0 2 10 1.0 7.2
Oil delivery pipe 1 (M10) M10 × 1.25 1 20 2.0 14
(M8) M8 × 1.25 2 18 1.8 13
Oil hose M6 × 1.0 2 8 0.8 5.8
Oil hose clamp—220.21.4
Oil strainer and frame M14 × 1.5 1 70 7.0 50
Carburetor joint clamp M4 × 0.7 2 3 0.3 2.2
Air filter joint clamp M6 × 1.0 1 3 0.3 2.2
Throttle cable (pull) M6 × 1.0 1 4 0.4 2.9
Throttle cable (return) M12 × 1.0 1 11 1.1 8.0
Throttle cable cover M5 × 0.8 2 4 0.4 2.9
Hot starter plunger M12 × 1.0 1 2 0.2 1.4
Air filter case M6 × 1.0 2 8 0.8 5.8
Air filter joint and air filter case M5 × 0.8 1 4 0.4 2.9
Air filter element M6 × 1.0 1 2 0.2 1.4
Exhaust pipe (nut) M8 × 1.25 1 13 1.3 9.4
(bolt) M8 × 1.25 1 24 2.4 17
Exhaust pipe protector M6 × 1.0 3 10 1.0 7.2
MAINTENANCE SPECIFICATIONS

2 - 18
SPECCABLE ROUTING DIAGRAM
EC240000
CABLE ROUTING DIAGRAM
1Fuel tank breather hose
2Clutch cable
3Oil tank breather hose
4Hot starter cable
5Cylinder head breather hose
6Cable guide
7Hose guide
8Brake hose
9Engine stop switch lead
0Clamp
ASub-wire harness
BThrottle position sensor lead
CNeutral switch lead
DOil hose
ECDI magneto lead
FRadiator breather hose
GCarburetor breather hose
HCarburetor overflow hoseÈInsert the end of the fuel tank
breather hose into the hole in
the steering stem cap.
ÉPass the hot starter cable
between the cylinder head
breather hose, oil tank breather
hose and ignition coil, then on
the outside of the left engine
bracket.
ÊPass the clutch cable through
the cable guides.
ËPass the clutch cable in front of
the radiator mounting boss.
ÌFasten the neutral switch lead
and CDI magneto lead to the
cable guide with a plastic locking
tie and cut off the tie end.ÍFasten the engine stop switch
lead, neutral switch lead and
CDI magneto lead.
ÎFasten the engine stop switch
lead and sub-wire harness at the
protecting tube for the engine
stop switch lead.
ÏFasten the sub-wire harness
and hot starter cable at the white
tape for the sub-wire harness.
ÐFasten the sub-wire harness.
ÑPass the sub-wire harness
between the engine brackets.
B
E
C
9
B
C
C
9
0
0
A
0
0
0
0
B 0 Ì
Í
Î
Ï
Ð
Ð
Ñ
Ò
Ó
C
D
0 0 0E F
Ô Õ Ö ×
1
2
3
4
5 6 6 8
7
Ê
Ê ËÈ
É
AGG
H
Ø
D
F
C