check engine YAMAHA WR 426F 2001 User Guide

3 - 12
INSP
ADJDECOMPRESSION LEVER ADJUSTMENT/
AIR FILTER CLEANING
DECOMPRESSION LEVER ADJUSTMENT
1. Check:
lDecompression lever free play
2. Adjust:
lDecompression lever free play
AIR FILTER CLEANING
NOTE:
Proper air filter maintenance is the biggest key
to preventing premature engine wear and
damage.
CAUTION:
Never run the engine without the air filter
element in place; this would allow dirt and
dust to enter the engine and cause rapid
wear and possible engine damage.Checking steps:
lRemove the timing plug.
lTurn the crankshaft counterclockwise to
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.
lCheck the free play c.
Free play:
5 ~ 9 mm (0.20 ~ 0.35 in)
Adjustment steps:
lLoosen the locknut 1.
lTurn the adjuster 2 in or out until the
adjustment is suitable.
lTighten the locknut.
CAUTION:
After the adjustment, start the engine
and make sure that the engine does not
stop when the handlebars are turned
fully both ways. If the decompression
cable is too tense, the engine will stop by
the decompression system.

3 - 14
INSP
ADJ
ENGINE OIL LEVEL INSPECTION
9. Apply:
lLithium soap base grease
On the matching surface a on air filter
element.
10. Install:
lAir filter element 1
lWasher
lFitting bolt
NOTE:
Align the projection a on filter guide with the
hole b in air filter case.
T R..2 Nm (0.2 m · kg, 1.4 ft · lb)
ENGINE OIL LEVEL INSPECTION
1. Stand the motorcycle on a level surface.
NOTE:
lWhen checking the oil level make sure that
the motorcycle is upright.
lPlace the motorcycle on a suitable stand.
WARNING
Never remove the oil tank cap just after
high speed operation. The heated oil could
spurt out. causing danger. Wait until the oil
cools down to approximately 70 ˚C (158 ˚F).
2. Idle the engine more than 3 minutes
while keeping the motorcycle upright.
Then stop the engine and inspect the oil
level.
3. Remove:
lOil tank cap 1

3 - 17
INSP
ADJ
ENGINE OIL REPLACEMENT
6. If the oil filter is to be replaced during this
oil change, remove the following parts
and reinstall them.
Replacement steps:
lRemove the exhaust pipe.
lRemove the oil filter cover 1 and oil filter
element 2.
lCheck the O-rings 3, if cracked or dam-
aged, replace them with a new one.
lInstall the oil filter element and oil filter
cover.
T R..
Oil filter cover:
10 Nm (1.0 m • kg, 7.2 ft • lb)
7. Install:
lPlain washer 1
lOil strainer (frame) 2
lEngine oil hose 3
lBolt (engine oil hose) 4
lEngine oil hose clamp 5
lEngine skid plate
New
T R..90 Nm (9.0 m · kg, 65 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
T R..2 Nm (0.2 m · kg, 1.4 ft · lb)
8. Install:
lGaskets
lOil filter drain bolt
lDrain bolt (crankcase)
lDrain bolt (frame)
New
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
T R..20 Nm (2.0 m · kg, 14 ft · lb)
T R..23 Nm (2.3 m · kg, 17 ft · lb)
9. Fill:
lOil tank (frame)
Oil quantity:
Total amount:
1.7 L (1.50 Imp qt, 1.80 US qt)
Periodic oil change:
1.5 L (1.32 Imp qt, 1.59 US qt)
With oil filter replacement:
1.6 L (1.41 Imp qt, 1.69 US qt)

3 - 18
INSP
ADJ
PILOT SCREW ADJUSTMENT
10. Install:
lOil filler plug
11. Inspect:
lEngine (for oil leaks)
lOil level
Refer to “ENGINE OIL LEVEL INSPEC-
TION”.
12. Check:
lOil pressure
PILOT SCREW ADJUSTMENT
1. Adjust:
lPilot screw 1
* Except for USAChecking steps:
lSlightly loosen the oil gallery bolt 1.
lStart the engine and keep it idling until oil
starts to seep from the oil gallery bolt. If no
oil comes out after one minute, turn the
engine off so it will not seize.
lCheck oil passages, oil filter and oil pump
for damage or leakage.
lStart the engine after solving the prob-
lem(s) and recheck the oil pressure.
lTighten the oil gallery bolt to specification.
T R..
Oil gallery bolt:
18 Nm (1.8 m • kg, 13 ft • lb)
Adjusting steps:
NOTE:
To optimize the fuel flow at a smaller throttle
opening, each machine’s pilot screw has
been individually set at the factory. Before
adjusting the pilot screw, turn it in fully and
count the number of turns. Record this num-
ber as the factory-set number of turns out.
lTurn in the pilot screw until it is lightly
seated.
lTurn out the pilot screw by the factory-set
number of turns.
Pilot screw:
WR426F: 1-5/8 turns out
* 7/8 turns out
WR400F: 1-1/2 turns out
(example)

3 - 19
INSP
ADJIDLE SPEED ADJUSTMENT/
VALVE CLEARANCE ADJUSTMENT
EC35M021
IDLE SPEED ADJUSTMENT
1. Start the engine and thoroughly warm it
up.
2. Adjust:
lIdle speed
Adjustment steps:
lAdjust the pilot screw.
Refer to “PILOT SCREW ADJUSTMENT”
section.
lTurn 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:
1,700 ~ 1,900 r/min
VALVE CLEARANCE ADJUSTMENT
NOTE:
lThe valve clearance should be adjusted
when the engine is cool to the touch.
lThe piston must be at Top Dead Center
(T.D.C.) on compression stroke to check or
adjust the valve clearance.
1. Remove:
lSeat
lFuel tank
Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section in the CHAPTER 4.
2. Remove:
lCarburetor
Refer to “CARBURETOR” section in
the CHAPTER 4.
lSpark plug cap
lEngine stay (upper)
lCylinder head cover
Refer to “CAMSHAFTS” section in the
CHAPTER 4.
3. Remove:
lTiming plug 1
lStraight plug 2
lO-ring

3 - 34
INSP
ADJ
DRIVE CHAIN SLACK ADJUSTMENT
5. Install:
lDrive chain 1
lJoint 2
lMaster link clip 3
CAUTION:
Be sure to install the master link clip to the
direction as shown.
aTurning direction
6. Lubricate:
lDrive chain
Drive chain lubricant:
SAE 10W-30 motor oil or suit-
able chain lubricants
New
EC36A060
DRIVE CHAIN SLACK ADJUSTMENT
1. Elevate the rear wheel by placing the
suitable stand under the engine.
2. Check:
lDrive chain slack a
Above the seal guard installation bolt.
Out of specification ® Adjust.
NOTE:
Before checking and/or adjusting, rotate the
rear wheel through several revolutions and
check the slack several times to find the tight-
est point. Check and/or adjust chain slack with
rear wheel in this “tight chain” position.
Drive chain slack:
40 ~ 50 mm (1.6 ~ 2.0 in)

3 - 44
INSP
ADJ
STEERING HEAD INSPECTION AND ADJUSTMENT
2. Inspect:
lBearing free play
Exist play ® Replace.
STEERING HEAD INSPECTION AND
ADJUSTMENT
1. Elevate the front wheel by placing a suit-
able stand under the engine.
2. Check:
lSteering shaft
Grasp the bottom of the forks and gen-
tly rock the fork assembly back and
forth.
Free play ® Adjust steering head.
3. Check:
lSteering smooth action
Turn the handlebar lock to lock.
Unsmooth action ® Adjust steering ring
nut.
4. Adjust:
lSteering ring nut
Steering ring nut adjustment steps:
lRemove the headlight.
lRemove the handlebar and handle crown.
lLoosen the ring nut 1 using the ring nut
wrench 2.
Ring nut wrench:
YU-33975/90890-01403

3 - 47
INSP
ADJ
ELECTRICAL/SPARK PLUG INSPECTION
EC370000
ELECTRICAL
EC371001
SPARK PLUG INSPECTION
1. Remove:
lSpark plug
2. Inspect:
lElectrode 1
Wear/damage ® Replace.
lInsulator color 2
Normal condition is a medium to light
tan color.
Distinctly different color ® Check the
engine condition.
NOTE:
When the engine runs for many hours at low
speeds, the spark plug insulator will become
sooty, even if the engine and carburetor are in
good operating condition.
3. Measure:
lPlug gap a
Use a wire gauge or thickness gauge.
Out of specification ® Re-gap.
Spark plug gap:
0.7 ~ 0.8 mm (0.028 ~ 0.031 in)
4. Clean the plug with a spark plug cleaner
if necessary.
5. Tighten:
lSpark plug
NOTE:
lBefore installing a spark plug, clean the gas-
ket surface and plug surface.
lFinger-tighten a the spark plug before
torquing to specification b.
T R..13 Nm (1.3 m · kg, 9.4 ft · lb)

3 - 48
INSP
ADJ
IGNITION TIMING CHECK
IGNITION TIMING CHECK
1. Remove:
lTiming plug 1
2. Attach:
lTiming light
lInductive tachometer
To the spark plug lead.
3. Check:
lIgnition timing
Timing light:
YM-33277-A/90890-03141
Inductive tachometer:
YU-08036-B
Engine tachometer:
90890-03113
Checking steps:
lStart the engine and let it warm up. Let the
engine run at the specified speed.
Engine speed:
1,700 ~ 1,900 r/min
lVisually check the stationary pointer a is
within the firing range b on the rotor.
Incorrect firing range ® Check rotor and
pickup assembly.
4. Install:
lTiming plug

4 - 74
ENGOIL PUMP
INSPECTION
Oil pump
1. Inspect:
lOil pump drive gear
lOil pump driven gear
lRotor housing
lOil pump cover
Cracks/wear/damage ® Replace.
2. Measure:
lTip clearance a
Between the inner rotor 1 and the
outer rotor 2.
lTip clearance b
Between the outer rotor 2 and the rotor
housing 3.
Out of specification ® Replace the oil
pump.
Tip clearance a:
0.12 mm or less
(0.0047 in or less)
: 0.20 mm (0.006 in)
Tip clearance b:
0.09 ~ 0.17 mm (0.0035 ~ 0.0067 in)
: 0.24 mm (0.009 in)
Side clearance c:
0.03 ~ 0.10 mm (0.0012 ~ 0.0039 in)
: 0.17 mm (0.007 in)
3. Check:
lUnsmooth ® Repeat steps #1 and #2
or replace the defective parts.
ASSEMBLY AND INSTALLATION
Oil pump
1. Install:
lOil pump drive shaft 1
lWasher 2
lPin 3
lInner rotor 1 4
NOTE:
lApply the engine oil on the oil pump drive
shaft and inner rotor 1.
lFit the pin into the groove in the inner rotor 1.