2014 YAMAHA WR 250F engine

5-7
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
(For EUROPE)
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"
• Main air jet "7"
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.
MEASURING 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.
Float height:
8.0 mm (0.31 in)

5-17
CAMSHAFTS
4. Measure:
• Camshaft-to-cap clearance
Out of specification→Measure
camshaft outside diameter.
Measurement steps:
a. Install the camshaft onto the cylin-
der head.
b. Position a strip of Plastigauge
®
"1" onto the camshaft.
c. Install the clip, dowel pins and
camshaft caps.
• Tighten the bolts (camshaft cap) in
a crisscross pattern from innermost
to outer caps.
• Do not turn the camshaft when
measuring clearance with the Plas-
tigauge
®.
d. Remove the camshaft caps and
measure the width of the Plasti-
gauge
® "1".
5. Measure:
• Camshaft outside diameter "a"
Out of specification→Replace the
camshaft.
Within specification→Replace
camshaft case and camshaft
caps as a set.CHECKING THE CAMSHAFT
SPROCKET
1. Inspect:
• Camshaft sprocket "1"
Wear/damage→Replace the
camshaft assembly and timing
chain as a set.
CHECKING THE
DECOMPRESSION SYSTEM
1. Check:
• Decompression system
Checking steps:
a. Check that the decompression
mechanism cam "1" moves
smoothly.
b. Check that the decompression
mechanism cam lever pin "2" proj-
ects from the camshaft.
CHECKING THE TIMING CHAIN
TENSIONER
1. Check:
• While pressing the tensioner rod
lightly with fingers, use a thin
screwdriver "1" and wind the ten-
sioner rod up fully clockwise.
• When releasing the screwdriver
by pressing lightly with fingers,
make sure that the tensioner rod
will come out smoothly.
• If not, replace the tensioner as-
sembly.INSTALLING THE CAMSHAFT
1. Install:
• Exhaust camshaft "1"
• Intake camshaft "2"
Installation steps:
a. Turn the crankshaft counterclock-
wise with a wrench.
• Apply the molybdenum disulfide oil
on the camshafts.
• Apply the engine oil on the decom-
pression system.
• Squeezing the decompression le-
ver allows the crankshaft to be
turned easily.
b. Align the T.D.C. mark "a" on the
rotor with the align mark "b" on the
crankcase cover when piston is at
T.D.C. on compression stroke.
c. Fit the timing chain "3" onto both
camshaft sprockets and install the
camshafts on the cylinder head. Camshaft-to-cap clear-
ance:
0.028–0.062 mm
(0.0011–0.0024 in)
:0.08 mm (0.003
in)
Bolt (camshaft cap):
10 Nm (1.0 m•kg, 7.2
ft•lb)
Camshaft outside diame-
ter:
21.959–21.972 mm
(0.8645–0.8650 in)

5-19
CYLINDER HEAD
CYLINDER HEAD
REMOVING THE CYLINDER HEAD
Order Part name Q'ty Remarks
Seat and fuel tank Refer to "REMOVING THE SEAT, FUEL
TANK AND SIDE COVERS" section in the
CHAPTER 3.
Exhaust pipe and silencerRefer to "REMOVING THE EXHAUST PIPE
AND SILENCER" section in the CHAPTER 3.
Radiator hose 1 Disconnect at cylinder head side.
Carburetor Refer to "CARBURETOR" section.
Air cut-off valve assembly Refer to "AIR INDUCTION SYSTEM" section.
Camshaft Refer to "CAMSHAFTS" section.
Upper engine bracket Refer to "ENGINE REMOVAL" section.
1 Radiator pipe 1
2 Oil delivery pipe 1
3Nut 2
4 Bolt [L = 135 mm (5.31 in)] 2
5 Bolt [L = 145 mm (5.71 in)] 2
6 Cylinder head 1
7 Timing chain guide (exhaust side) 1

5-24
VALVES AND VALVE SPRINGS
h. Press the valve through the valve
guide and onto the valve seat to
make a clear pattern.
i. Measure the valve seat width
again. If the valve seat width is out
of specification, reface and relap
the valve seat.
CHECKING THE VALVE SPRINGS
1. Measure:
• Valve spring free length "a"
Out of specification→Replace.
2. Measure:
• Compressed spring force "a"
Out of specification→Replace.
b. Installed length
3. Measure:
• Spring tilt "a"
Out of specification→Replace.CHECKING THE VALVE LIFTERS
1. Inspect:
• Valve lifter
Scratches/damage→Replace
both lifters and cylinder head.
INSTALLING THE VALVES
1. Apply:
• Molybdenum disulfide oil
Onto the valve stem and valve
stem seal.
2. Install:
• Valve "1"
• Valve spring seat "2"
• Valve stem seal "3"
• Valve spring "4"
• Valve spring retainer "5"
To cylinder head.
• Make sure that each valve is in-
stalled in its original place, also re-
ferring to the painted color as
follows.
Intake (middle) "a": Orange
Intake (right/left) "b": Green
Exhaust "c": Purple
• Install the valve springs with the
larger pitch "d" facing upward.
e. Smaller pitch3. Install:
• Valve cotter
Install the valve cotters by compress-
ing the valve spring with the valve
spring compressor "1" and the valve
spring compressor attachment "2".
4. To secure the valve cotters onto
the valve stem, lightly tap the
valve tip with a piece of wood.
Hitting the valve tip with excessive
force could damage the valve.
5. Install:
• Adjusting pad "1"
• Valve lifter "2"
• Apply the molybdenum disulfide oil
on the valve stem end.
• Apply the engine oil on the valve lift-
ers.
• Valve lifter must turn smoothly
when rotated with a finger.
• Be careful to reinstall valve lifters
and pads in their original place.
Free length (valve
spring):
Intake:
36.58 mm (1.44 in)
: 35.58 mm
(1.40 in)
Exhaust:
37.54 mm (1.48 in)
: 36.54 mm
(1.44 in)
Compressed spring
force:
Intake:
103.00–118.60 N at
29.13 mm (10.50–
12.09 kg at 29.13 mm,
23.15–26.66 lb at 1.15
in)
Exhaust:
126.00–144.00 N at
29.30 mm (12.85–
14.68 kg at 29.30 mm,
28.32–32.37 lb at 1.15
in)
Spring tilt limit:
Intake:
2.5°/1.6 mm (0.06 in)
Exhaust:
2.5°/1.6 mm (0.06 in)
Valve spring compres-
sor:
YM-04019/90890-04019
Valve spring compressor
adapter 19.5 mm:
YM-04114
Valve spring compressor
attachment:
90890-04114

5-27
CYLINDER AND PISTON
a. 10 mm (0.39 in)
3. Measure:
• Ring end gap
Out of specification→Replace.
You cannot measure the end gap on
the expander spacer of the oil control
ring. If the oil control ring rails show
excessive gap, replace all three rings.
CHECKING THE PISTON PIN
1. Inspect:
• Piston pin
Blue discoloration/grooves→Re-
place, then inspect the lubrication
system.
2. Measure:
• Piston pin-to-piston clearance
Measurement steps:
a. Measure the outside diameter
(piston pin) "a".
If out of specification, replace the
piston pin.b. Measure the inside diameter (pis-
ton) "b".
c. Calculate the piston pin-to-piston
clearance with the following for-
mula.
d. If out of specification, replace the
piston.
INSTALLING THE PISTON RING
AND PISTON
1. Install:
•Piston ring
Onto the piston.
• Be sure to install the piston rings so
that the manufacturer's marks or
numbers are located on the upper
side of the rings.
• Lubricate the piston and piston
rings liberally with engine oil.
2. Position:
•Top ring
• 2nd ring
• Oil ring
Offset the piston ring end gaps as
shown.a. Top ring end
b. 2nd ring end
c. Oil ring end (upper)
d. Oil ring
e. Oil ring end (lower)
3. Install:
• Piston "1"
• Piston pin "2"
• Piston pin clip "3"
• Apply engine oil onto the piston pin
and piston.
• Be sure that the arrow mark "a" on
the piston points to the exhaust side
of the engine.
• Before installing the piston pin clip,
cover the crankcase with a clean
rag to prevent the piston pin clip
from falling into the crankcase.
• Install the piston pin clips with their
ends facing downward.End gap:
Standard
Top
ring0.15–0.25 mm
(0.0059–0.0098
in)0.50
mm
(0.020
in)
2nd
ring0.30–0.45 mm
(0.0118–0.0177
in)0.80
mm
(0.031
in)
Oil
ring0.10–0.40 mm
(0.0039–0.0157
in)—
Outside diameter (piston
pin):
15.991–16.000 mm
(0.6296–0.6299 in)
Inside diameter (piston):
16.002–16.013 mm
(0.6300–0.6304 in)
Piston pin-to-piston clearance =
Inside diameter (piston) "b" -
Outside diameter (piston pin)
"a"
Piston pin-to-piston
clearance:
0.002–0.022 mm
(0.0001–0.0009 in)
:0.07 mm (0.003
in)
New

5-28
CYLINDER AND PISTON
INSTALLING THE CYLINDER
1. Lubricate:
•Piston
• Piston ring
• Cylinder
Apply a liberal coating of engine oil.
2. Install:
• Dowel pin "1"
• O-ring "2"
Apply the lithium soap base grease
on the O-ring.
3. Install:
• Cylinder gasket "1"
• Cylinder "2"
Install the cylinder with one hand
while compressing the piston rings
with the other hand.
• Pass the timing chain "3"
through the timing chain cavity.
• Be careful not to damage the tim-
ing chain guide "4" during instal-
lation.
4. Install:
• Bolt (cylinder) "5"
Bolt (cylinder):
10 Nm (1.0 m•kg, 7.2
ft•lb)

5-29
CLUTCH
CLUTCH
REMOVING THE CLUTCH
Order Part name Q'ty Remarks
Drain the engine oil. Refer to "CHANGING THE ENGINE OIL"
section in the CHAPTER 3.
Brake pedal Refer to "ENGINE REMOVAL" section.
Clutch cable Disconnect at engine side.
1 Clutch cover 1
2 Clutch spring 5
3 Pressure plate 1
4 Push rod 1 1
5 Circlip 1
6 Washer 1
7 Bearing 1
8Ball 1
9 Push rod 2 1
10 Friction plate 9
11 Clutch plate 8
12 Cushion spring 1
13 Seat plate 1

5-31
CLUTCH
REMOVING THE CLUTCH BOSS
1. Remove:
•Nut "1"
• Lock washer "2"
• Clutch boss "3"
Straighten the lock washer tab and
use the clutch holding tool "4" to hold
the clutch boss.
A. For USA and CDN
B. Except for USA and CDN
CHECKING THE CLUTCH
HOUSING AND BOSS
1. Inspect:
• Clutch housing "1"
Cracks/wear/damage→Replace.
• Clutch boss "2"
Scoring/wear/damage → Re-
place.
CHECKING THE PRIMARY DRIVEN
GEAR
1. Check:
• Circumferential play
Free play exists→Replace.
• Gear teeth "a"
Wear/damage→Replace.CHECKING THE CLUTCH
SPRINGS
1. Measure:
• Clutch spring free length "a"
Out of specification→Replace
springs as a set.
CHECKING THE FRICTION
PLATES
1. Measure:
• Friction plate thickness
Out of specification→Replace
friction plate as a set.
Measure at all four points.
CHECKING THE CLUTCH PLATES
1. Measure:
• Clutch plate warpage
Out of specification→Replace
clutch plate as a set.
Use a surface plate "1" and thick-
ness gauge "2".CHECKING THE PUSH LEVER
SHAFT
1. Inspect:
• Push lever shaft "1"
Wear/damage→Replace.
CHECKING THE PUSH ROD
1. Inspect:
• Push rod 1 "1"
• Bearing "2"
• Washer "3"
• Push rod 2 "4"
•Ball "5"
Wear/damage/bend→Replace.
INSTALLING THE PUSH LEVER
SHAFT
1. Install:
• Push lever shaft "1"
• Bolt (push lever shaft) "2"
• Apply the lithium soap base grease
on the oil seal lip.
• Apply the engine oil on the push le-
ver shaft.
• Fit the seat plate "3" in the groove
"a" of the push lever shaft and tight-
en the bolt (seat plate).
Clutch holding tool:
YM-91042/90890-04086
Clutch spring free
length:
37.00 mm (1.46 in)
: 36.00 mm
(1.42 in)
Friction plate thickness:
2.90–3.10 mm (0.114–
0.122 in)
: 2.70 mm
(0.106 in)
Warp limit:
0.10 mm (0.004 in)
Bolt (push lever shaft):
10 Nm (1.0 m•kg, 7.2
ft•lb)