2010 YAMAHA YZ250F stop start

3-6
ENGINE
ENGINE
CHECKING THE COOLANT LEVEL
Do not remove the radiator cap
"1", drain bolt and hoses when the
engine and radiator are hot. Scald-
ing hot fluid and steam may be
blown out under pressure, which
could cause serious injury. When
the engine has cooled, place a
thick towel over the radiator cap,
slowly rotate the cap counter-
clockwise to the detent. This pro-
cedure allows any residual
pressure to escape. When the
hissing sound has stopped, press
down on the cap while turning
counterclockwise and remove it.
Hard water or salt water is harmful
to the engine parts. You may use
distilled water, if you can't get soft
water.
1. Place the machine on a level place, and hold it in an upright po-
sition.
2. Remove: • Radiator cap
3. Check: • Coolant level "a"Coolant level low →Add coolant.
1. Radiator
CHANGING THE COOLANT
Do not remove the radiator cap
when the engine is hot.
Take care so that coolant does not
splash on painted surfaces. If it
splashes, wash it away with water.
1. Place a container under the en- gine.
2. Remove: • Coolant drain bolt "1"
3. Remove: • Radiator capDrain the coolant completely.
4. Clean:
• Cooling systemThoroughly flush the cooling sys-
tem with clean tap water.
5. Install: • Copper washer
• Coolant drain bolt
6. Fill: • Radiator
•EngineTo specified level.
• Do not mix more than one type of
ethylene glycol antifreeze con-
taining corrosion inhibitors for
aluminum engine.
• Do not use water containing im- purities or oil.
Handling notes of coolant:
The coolant is harmful so it should be
handled with special care.
• When coolant splashes to your
eye.
Thoroughly wash your eye with
water and see your doctor.
• When coolant splashes to your clothes.
Quickly wash it away with water
and then with soap.
• When coolant is swallowed. Quickly make him vomit and take
him to a doctor.
7. Install:• Radiator cap
Start the engine and warm it up
for a several minutes.
8. Check:
• Coolant levelCoolant level low →Add coolant.
CHECKING THE RADIATOR CAP
1. Inspect: • Seal (radiator cap) "1"
• Valve and valve seat "2"Crack/damage →Replace.
Exist fur deposits "3" →Clean or
replace.
CHECKING THE RADIATOR CAP
OPENING PRESSURE
1. Attach: • Radiator cap tester "1" and adapt-er "2"
Apply water on the radiator cap seal.
Coolant drain bolt:
10 Nm (1.0 m•kg, 7.2
ft•lb)
Recommended coolant: High quality ethylene
glycol anti-freeze con-
taining anti -corrosion
for aluminum engine
Coolant "1" and water
(soft water) "2" mixing ra-
tio: 50%/50%
Coolant capacity: 1.00 L (0.88 Imp qt, 1.06
US qt)
Radiator cap tester:
YU-24460-01/90890-
01325
Radiator cap tester
adapter: YU-33984/90890-01352

4-11
CARBURETOR
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.
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"

4-12
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 (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.
15. Install:• Jet needle "1"
•Collar "2"
• Spring "3"
• Needle holder "4"
• Throttle valve plate "5"To throttle valve "6".
16. Install: • Throttle valve assembly "1"
• Screw (throttle shaft) "2"
Install the valve lever rollers "3" into
the slits "a" of the throttle valve.
Pilot screw (example): 1-3/4 turns out

5-24
HANDLEBAR
HANDLEBAR
REMOVING THE HANDLEBAROrder Part name Q'ty Remarks Number plate Remove the band only.
1 Hot starter cable 1 Disconnect at the lever side.
2 Hot starter lever holder 1
3 Clutch cable 1 Disconnect at the lever side.
4 Clutch lever holder 1
5 Engine stop switch 1
6 Brake master cylinder 1 Refer to removal section.
7 Throttle cable cap 1
8 Throttle cable #1 (pulled) 1 Disconnect at the throttle side.
9 Throttle cable #2 (pushed) 1 Disconnect at the throttle side.
10 Right grip 1 Refer to removal section.
11 Tube guide 1
12 Collar 1
13 Left grip 1 Refer to removal section.
14 Handlebar upper holder 2
15 Handlebar 1
16 Handlebar lower holder 2

5-26
HANDLEBAR
3. Tighten:• Nut (handlebar lower holder) "1"
4. Install: • Left grip "1"Apply the adhesive to the handle-
bar "2".
• Before applying the adhesive, wipe off grease or oil on the handlebar
surface "a" with a lacquer thinner.
• Install the left grip to the handlebar so that the line "b" between the two
arrow marks faces straight upward.
5. Install:• Right grip "1"
•Collar "2"Apply the adhesive on the tube
guide "3".
• Before applying the adhesive, wipe
off grease or oil on the tube guide
surface "a" with a lacquer thinner.
• Install the grip to the tube guide so
that the grip match mark "b" and
tube guide slot "c" form the angle as
shown.
6. Install:• Collar "1"
• Grip cap cover "2"
• Throttle grip "3"
Apply the lithium soap base grease
on the throttle grip sliding surface.
7. Install:• Throttle cables "1"
To tube guide "2".
Apply the lithium soap base grease
on the throttle cable end and tube
guide cable winding portion.
8. Install:• Throttle cable cap "1"
• Screw (throttle cable cap) "2"
After tightening the screws, check
that the throttle grip "3" moves
smoothly. If it does not, retighten
the bolts for adjustment.
9. Install:• Grip cap cover "1"
• Cover (throttle cable cap) "2"
10. Install: • Brake master cylinder "1"
• Brake master cylinder bracket "2"
• Bolt (brake master cylinder brack-et) "3"
• Install the bracket so that the arrow
mark "a" faces upward.
• First tighten the bolt on the upper side of the brake master cylinder
bracket, and then tighten the bolt on
the lower side.
11. Install:
• Engine stop switch "1"
• Clutch lever holder "2"
• Bolt (clutch lever holder) "3"
• Hot starter lever holder "4"
• Bolt (hot starter lever holder) "5"
Nut (handlebar lower
holder):
34 Nm (3.4 m•kg, 24
ft•lb)
Screw (throttle cable
cap):4 Nm (0.4 m•kg, 2.9
ft•lb)
Bolt (brake master cylin-
der bracket): 9 Nm (0.9 m•kg, 6.5
ft•lb)
Bolt (clutch lever holder): 5 Nm (0.5 m•kg, 3.6
ft•lb)
Bolt (hot starter lever
holder): 4 Nm (0.4 m•kg, 2.9
ft•lb)

5-27
HANDLEBAR
• Clamp "6"
• The engine stop switch, clutch lever holder and clamp should be in-
stalled according to the dimensions
shown.
• Pass the engine stop switch lead in the middle of the clutch lever hold-
er.
12. Install:• Clutch cable "1"
• Hot starter cable "2"
Apply the lithium soap base grease
on the clutch cable end and hot start-
er cable end.
13. Adjust:
• Clutch lever free playRefer to "ADJUSTING THE
CLUTCH CABLE FREE PLAY"
section in the CHAPTER 3.
• Hot starter lever free play Refer to "ADJUSTING THE HOT
STARTER LEVER FREE PLAY"
section in the CHAPTER 3.

6-4
IGNITION SYSTEM
SPARK GAP TEST
1. Disconnect the ignition coil from spark plug.
2. Remove the ignition coil cap.
3. Connect the dynamic spark tester "1" (ignition ch ecker "2") as
shown.
• Ignition coil "3"
• Spark plug "4"
A. For USA and CDN
B. Except for USA and CDN
4. Kick the kickstarter crank.
5. Check the ignition spark gap.
6. Start engine, and increase spark gap until misfire occurs. (for USA
and CDN only)
CHECKING THE COUPLERS,
LEADS AND IGNITION COIL
CONNECTION
1. Check: • Couplers and leads connection
Rust/dust/looseness/short-circuit
→ Repair or replace.
• Ignition coil and spark plug as
they are fitted
Push in the ignition coil until it
closely contacts the spark plug
hole in the cylinder head cover. CHECKING THE ENGINE STOP
SWITCH
1. Inspect:
• Engine stop switch conduction
Not conductive while it is pushed →
Replace.
Conductive while it is freed →Re-
place.
Set the tester selection position to " Ω
× 1".
CHECKING THE IGNITION COIL
1. Remove the ignition coil cap.
2. Inspect: • Primary coil resistance
Out of specification →Replace. 3. Inspect:
• Secondary coil resistanceOut of specification →Replace.
4. Inspect: • Sealed portion of ignition coil "a"
• Spark plug terminal pin "b"
• Threaded portion of spark plug "c"Wear →Replace.
CHECKING THE CDI MAGNETO
1. Inspect: • Pickup coil resistance
Out of specification →Replace.
Minimum spark gap:
6.0 mm (0.24 in)
Tester (+) lead →Black/White lead
"1"
Tester (-) lead →Black lead "2"
Result Conductive (while the
engine stop switch is
pushed)
Tester (+) lead →Orange lead "1"
Tester (-) lead →Black lead "2"
Primary
coil resis-
tance Tester se-
lector posi-
tion
0.08–0.10
Ω at 20 °C (68 °F) Ω × 1
/W
BB
Tester (+) lead →Orange lead "1"
Tester (-) lead →Spark plug termi-
nal "2"
Secondary coil resis- tance Tester se-
lector posi- tion
4.6–6.8
k Ωat 20 °C
(68 °F) k
Ω × 1
Tester (+) lead →Red lead "1"
Tester (-) lead →White lead "2"
Pickup coil resistance Tester se-
lector posi-
tion
248-372 Ω
at 20 °C (68 °F) Ω
×100
B
WBr
G P
R

6-8
THROTTLE POSITION SENSOR SYSTEM
8. Start the engine.
9. Adjust:• Throttle position sensor output voltage
Adjustment steps:
a. Adjust the installation angle of the throttle position sensor "1" to ob-
tain the specified output voltage.
Measure the output voltage accurate-
ly with a digital electronic voltmeter
that gives an easy reading of a small
voltage.
10. Put the aligning marks "a" on the throttle position sensor and car-
buretor.
11. Stop the engine.
12. Remove the carburetor.
13. Tighten: • Screw (throttle position sensor) "1"
Tighten the screw (throttle position
sensor) using the T25 bit.
14. Install the carburetor. CHECKING THE THROTTLE
POSITION SENSOR INPUT
VOLTAGE
1. Disconnect the throttle position
sensor coupler.
2. Start the engine.
3. Inspect:
• Throttle position sensor input volt-age
Out of specification →Replace the
CDI unit.
Throttle po- sition sen-
sor output voltage Tester se-
lector posi- tion
0.58–0.78 V DCV
Tester (+) lead →Blue lead "1"
Tester (-) lead →Black/Blue lead
"2"
Throttle po-sition sen- sor input voltage Tester se-
lector posi-
tion
4–6 V DCV-20
LY
B/L