2001 YAMAHA YZ426F fuel

2 - 21
SPEC

CABLE ROUTING DIAGRAM
EC240000
CABLE ROUTING DIAGRAM
1
Hose guide
2
Brake hose
3
Fuel tank breather hose
4
Oil tank breather hose
5
Clamp
6
“ENGINE STOP” button lead
7
Sub wire harness
8
TPS (throttle position
sensor) lead
9
Neutral switch lead
0
Oil hose
A
Hose holder
B
CDI magneto lead
C
Clutch cable
D
Cylinder head breather hose
E
Carburetor breather hose
F
Overflow hose

Pass the clutch cable through
the cable guide.
õ
Pass the fuel tank breather hose
between the handlebar and ten-
sion bar, then insert its end into
the hole of the number plate.
‚
Pass the decompression cable
and “ENGINE STOP” button
lead under the frame.
ë
Fasten the CDI magneto lead,
neutral switch lead and
“ENGINE STOP” button lead to
the frame with a plastic locking
tie and cut off the tie end.
ä
Pass the “ENGINE STOP” but-
ton lead along the inner side of
the oil tank breather hose.
ì
Fasten the sub wire harness
and “ENGINE STOP” button
lead to the frame in front of the
protector of the sub wire har-
ness with a plastic locking tie
and cut off the tie end.
í
Pass the cylinder head breather
hose along the right side of the
oil tank breather hose.
î
Pass the sub wire harness
between the engine brackets.
é
Fasten the sub wire harness
and “ENGINE STOP” button
lead to the frame at the rear of
the protector of the sub wire har-
ness with a plastic locking tie
and cut off the tie end.

3 - 2
INSP
ADJ

MAINTENANCE INTERVALS
SHIFT FORK, SHIFT CAM, GUIDE BAR
Inspect
c
Inspect wear
ROTOR NUT
Retighten
c

c

MUFFLER
Inspect and retighten
Clean
Replace
c

c

c

c
* Whichever comes first
CRANK
Inspect and clean
c

c

CARBURETOR
Inspect, adjust and clean
c

c
When using a high-pres-
sure washer, make sure
that water does not enter
the accelerator pump.
SPARK PLUG
Inspect and clean
Replace
c

c

c

DRIVE CHAIN
Lubricate, slack, alignment
Replace
c

c

c
Use chain lube
Chain slack: 40 ~ 50 mm
(1.6 ~ 2.0 in)
COOLING SYSTEM
Check coolant level and leakage
Check radiator cap operation
Replace coolant
Inspect hoses
c

c

c

c

c
Every two years
OUTSIDE NUTS AND BOLTS
Retighten
c

c
Refer to “STARTING
AND BREAK-IN” section
in the CHAPTER 1.
AIR FILTER
Clean and lubricate
Replace
c

c

c
Use foam air-filter oil
OIL STRAINER (frame)
Clean
c

FRAME
Clean and inspect
c

c

FUEL TANK, COCK
Clean and inspect
c

c

BRAKES
Adjust lever position and pedal height
Lubricate pivot point
Check brake disc surface
Check fluid level and leakage
Retighten brake disc bolts, caliper
bolts, master cylinder bolts and union
bolts
Replace pads
Replace brake fluid
c

c

c

c

c

c

c

c

c

c

c

c
Every one year
FRONT FORKS
Inspect and adjust
Replace oil
Replace oil seal
c

c

c

c

c
Suspension oil “01”
FRONT FORK OIL SEAL AND DUST
SEAL
Clean and lube
c

c
Lithium base grease ItemAfter
break-inEvery
race
Every
third
(or
500 km)Every
fifth
(or
1,000 km)
As re-
quiredRemarks


3

3 - 4
INSP
ADJ
PRE-OPERATION INSPECTION AND MAINTENANCE
EC320000
PRE-OPERATION INSPECTION AND MAINTENANCE
Before riding for break-in operation, practice or a race, make sure the machine is in good operating
condition.
Before using this machine, check the following points.
GENERAL INSPECTION AND MAINTENANCE
Item Routine Page
CoolantCheck that coolant is filled up to the radiator filler cap.
Check the cooling system for leakage.P.3-5 ~ 9
FuelCheck that a fresh gasoline is filled in the fuel tank. Check the
fuel line for leakage.P.1-13 ~ 14
Engine oilCheck that the oil level is correct. Check the crankcase and
frame oil line for leakage.P.3-13 ~ 17
Gear shifter and clutchCheck that gears can be shifted correctly in order and that the
clutch operates smoothly.P.3-9
Throttle grip/HousingCheck that the throttle grip operation and free play are correctly
adjusted. Lubricate the throttle grip and housing, if necessary.P.3-10 ~ 11
Brakes Check the play of front brake and effect of front and rear brake. P.3-24 ~ 30
ChainCheck chain slack and alignment. Check that the chain is lubri-
cated properly.P.3-31 ~ 33
WheelsCheck for excessive wear and tire pressure. Check for loose
spokes and have no excessive play.P.3-41 ~ 42
SteeringCheck that the handlebar can be turned smoothly and have no
excessive play.P.3-42 ~ 43
Front forks and rear shock
absorberCheck that they operate smoothly and there is no oil leakage. P.3-33 ~ 40
Cables (wires)Check that the clutch and throttle cables move smoothly. Check
that they are not caught when the handlebars are turned or
when the front forks travel up and down.—
Muffler Check that the muffler is tightly mounted and has no cracks. —
Sprocket Check that the driven sprocket tightening bolt is not loose. P.3-31
Lubrication Check for smooth operation. Lubricate if necessary. P.3-44
Bolts and nuts Check the chassis and engine for loose bolts and nuts. P.1-18
Lead connectorsCheck that the CDI magneto, CDI unit, and ignition coil are con-
nected tightly.P.1-6
SettingsIs the machine set suitably for the condition of the racing course
and weather or by taking into account the results of test runs
before racing? Are inspection and maintenance completely
done?P.7-1 ~ 21

3 - 17
INSP
ADJ
PILOT SCREW ADJUSTMENT
12. Check:
lOil pressure
Checking 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)
PILOT SCREW ADJUSTMENT
1. Adjust:
lPilot screw 1
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:
1-1/4 turns out (example)

3 - 18
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 - 43
INSP
ADJ
STEERING HEAD INSPECTION AND ADJUSTMENT
lTighten the ring nut 3 using ring nut
wrench 4.
NOTE:
Set the torque wrench to the ring nut wrench
so that they form a right angle.
Ring nut wrench:
YU-33975/90890-01403
T R..
Ring nut (initial tightening):
38 Nm (3.8 m • kg, 27 ft • lb)
lLoosen the ring nut one turn.
lRetighten the ring nut using the ring nut
wrench.
WARNING
Avoid over-tightening.
T R..
Ring nut (final tightening):
7 Nm (0.7 m • kg, 5.1 ft • lb)
lCheck the steering shaft by turning it lock
to lock. If there is any binding, remove the
steering shaft assembly and inspect the
steering bearings.
lInstall the handle crown 5, steering shaft
nut 6, handlebar 7, handlebar holder 8
and number plate 9.
NOTE:
lThe upper handlebar holder should be
installed with the punched mark a for-
ward.
lInsert the end of fuel breather hose 0 into
the hole of the number plate.
CAUTION:
First tighten the bolts on the front side of
the handlebar holder, and then tighten
the bolts on the rear side.
T R..
Steering shaft nut:
145 Nm (14.5 m • kg, 105 ft • lb)
Handlebar upper holder:
28 Nm (2.8 m • kg, 20 ft • lb)
Pinch bolt (handle crown):
23 Nm (2.3 m • kg, 17 ft • lb)
Number plate:
7 Nm (0.7 m • kg, 5.1 ft • lb)

4 - 1
ENG

EC400000
ENGINE
EC4R0000
SEAT, FUEL TANK AND SIDE COVERS
Extent of removal:
1
Seat removal
2
Fuel tank removal
3
Side covers removal
4
Number plate removal
Extent of removal Order Part name Q’ty Remarks
Preparation for removal
SEAT, FUEL TANK AND SIDE
COVERS REMOVAL
Turn the fuel cock to “OFF”.
Disconnect the fuel hose.
1 Seat 1
2 Air scoop (left and right) 2
3 Fitting band 1 Remove on fuel tank side.
4 Bolt (fuel tank) 2
5 Fuel tank 1
6 Side cover (left) 1
7 Side cover (right) 1
8 Number plate 1
13
4
2
3

SEAT, FUEL TANK AND SIDE COVERS
4



4

4 - 2
ENG

EXHAUST PIPE AND SILENCER
EC4S0000
EXHAUST PIPE AND SILENCER

Except for USA
Extent of removal:
1
Silencer removal
2
Exhaust pipe removal
Extent of removal Order Part name Q’ty Remarks
EXHAUST PIPE AND
SILENCER REMOVAL
Preparation for removal Side cover (right) Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
1 Bolt (clamp) 1 Only loosening.
2 Bolt [silencer (front)] 1
3 Bolt [silencer (rear)] 1
4 Collar 1
5 Silencer 1
6 Clamp 1
7 Nut (exhaust pipe) 1
8 Bolt (exhaust pipe) 1
9 Exhaust pipe 1
10 Gasket 2
2
1
2