2002 YAMAHA YZ426F engine

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GEN
INFO
CONTROL FUNCTIONS
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 KNOB
The hot starter knob (red) 1 is used when
starting a warm engine.
Use the hot starter knob when starting the
engine again immediately after it was stopped
(the engine is still warm). Pulling out the hot
starter knob injects secondary air to thin the
air-fuel mixture temporarily, allowing the
engine to be started more easily.
CAUTION:
After the engine has started, be sure to
push the hot starter knob back in.

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GEN
INFO
FUEL
Always use the recommended fuel as stated
below. Also, be sure to use new gasoline the
day of a race.
CAUTION:
Use only unleaded gasoline. The use of
leaded gasoline will cause severe damage
to the engine internal parts such as valves,
piston rings, and exhaust system, etc.
NOTE:
If knocking or pinging occurs, use a different
brand of gasoline or higher octane grade.
Recommended fuel:
Except for ZA:
Premium unleaded gasoline
only with a research octane
number of 95 or higher.
For ZA:
Premium gasoline
FUEL

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GEN
INFO
STARTING AND BREAK-IN
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 motorcycle 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.
Never use the decompression lever after
the engine is started. The engine may be
damaged if you use the decompression
lever while it is running.
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.
5. Without pulling in the decompression
lever, slowly depress the kick starter until
the compression stroke is found. When
considerable resistance of the kick starter
is felt, the engine is on the compression
stroke. If the engine is on the exhaust
stroke, resistance will only be felt when
the kick starter is initially depressed, not
through the entire range of depression
(as when the engine is on the compres-
sion stroke); therefore, depress the kick
starter a few more times.

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GEN
INFO
STARTING AND BREAK-IN
6. Pull the decompression lever to the han-
dlebar and depress the kick starter 10 ~
20˚.
7. Release the decompression lever and
return the kick starter to its original posi-
tion and then kick the kick starter.
WARNING
Do not open the throttle while kicking the
kick starter. Otherwise, the kick starter may
kick back.
8. Return the cold starter knob to its original
position and run the engine at 3,000 ~
5,000 r/min for 1 or 2 minutes.
NOTE:
Since this model is equipped with an accelera-
tor pump, if the engine is raced (the throttle
opened and closed), the air/fuel mixture will be
too rich and the engine may stall. Also unlike a
two-stroke engine, this model can idle.
CAUTION:
Do not warm up the engine for extended
periods of time.

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GEN
INFO
STARTING AND BREAK-IN
STARTING A WARM ENGINE
Do not operate the cold starter knob and throt-
tle. Open the hot starter knob (red) and start
the engine by kicking the kick starter forcefully
with a firm stroke.
As soon as the engine starts, push in the hot
starter knob to close the air passage.
Restarting an engine after a fall
Pull the hot starter knob (red) and start the
engine. As soon as the engine starts, push in
the hot starter knob to close the air passage.
The engine fails to start
Pull the hot starter knob (red) all the way out,
pull the decompression lever to the handlebar,
and while holding the lever, kick the kick
starter 10 to 20 times to clear the engine.
Then, restart the engine.
Refer to “Restarting an engine after a fall”.
* Operate the throttle grip before kick starting.
CAUTION:
Observe the following break-in procedures
during initial operation to ensure optimum
performance and avoid engine damage.
Throttle
grip oper-
ation*Cold
starter
knobHot
starter
knob (red)
Starting a cold engine
Air temperature = less than
5 ˚C (41 ˚F)Open 3
or 4 timesON OFF
Air temperature = more
than 5 ˚C (41 ˚F)None ON OFF
Air temperature (normal tem-
perature) = between 5 ˚C
(41 ˚F) and 25 ˚C (77 ˚F)None ON/OFF OFF
Air temperature = more
than 25 ˚C (77 ˚F)None OFF OFF
Starting an engine after a long
period of timeNone ON OFF
Restarting a warm engine None OFF ON
Restarting an engine after a fall None OFF ON

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GEN
INFO
BREAK-IN PROCEDURES
1. Before starting the engine, fill the fuel
tank with the fuel.
2. Perform the pre-operation checks on the
machine.
3. Start and warm up the engine. Check the
idle speed, and check the operation of
the controls and the “ENGINE STOP”
button. Then, restart the engine and
check its operation within no more than 5
minutes after it is restarted.
4. Operate the machine in the lower gears
at moderate throttle openings for five to
eight minutes.
5. Check how the engine runs when the
motorcycle is ridden with the throttle 1/4
to 1/2 open (low to medium speed) for
about one hour.
6. Restart the engine and check the opera-
tion of the machine throughout its entire
operating range. Restart the machine
and operate it for about 10 to 15 more
minutes. The machine will now be ready
to race.
CAUTION:
After the break-in or before each race,
you must check the entire machine for
loose fittings and fasteners as per
“TORQUE-CHECK POINTS”.
Tighten all such fasteners as required.
When any of the following parts have
been replaced, they must be broken in.
CYLINDER AND CRANKSHAFT:
About one hour of break-in operation is
necessary.
PISTON, RING, VALVES, CAMSHAFTS
AND GEARS:
These parts require about 30 minutes of
break-in operation at half-throttle or less.
Observe the condition of the engine care-
fully during operation.
STARTING AND BREAK-IN

GEN
INFO
EINFAHRVORSCHRIFTEN
1. Vor dem Anlassen des Motors volltan-
ken.
2. Die “ROUTINEKONTROLLE VOR
FAHRTBEGINN” ausführen.
3. Den Motor anlassen und warmlaufen las-
sen. Dabei die Leerlaufdrehzahl überwa-
chen und die Funktion der Bedienungs-
elemente sowie des Motorstoppschalters
“ENGINE STOP” prüfen. Innerhalb der
nächsten fünf Minuten den Motor wieder
anlassen und die folgenden Schritte aus-
führen.
4. Die Maschine fünf bis acht Minuten lang
bei mäßiger Gasdrehgrifföffnung in den
unteren Gängen fahren.
5. Den Motorbetrieb etwa eine Stunde lang
bei 1/4 bis 1/2 geöffnetem Gasdrehgriff
(niedrige bis mittlere Geschwindigkeit)
überprüfen.
6. Den Motor erneut anlassen und den Mo-
torbetrieb im gesamten Betriebsbereich
überprüfen. Den Motor abschalten und
noch einmal anlassen und die Maschine
10 bis 15 Minuten betreiben. Danach ist
die Maschine für Rennen einsatzbereit.
ACHTUNG:
Nach dem Einfahren und vor jedem Ren-
nen die Schraubverbindungen gemäß der
Tabelle “ANZUGSMOMENTE KONTROL-
LIEREN” auf festen Sitz prüfen und vor-
schriftsmäßig anziehen.
Nach der Erneuerung eines der folgenden
Teile muß die Maschine erneut eingefah-
ren werden.
- ZYLINDER UND KURBELWELLE
Etwa eine Stunde Einfahrzeit
- KOLBEN, KOLBENRINGE, VENTILE,
NOKKENWELLEN UND -RÄDER:
Etwa 30 Minuten Einfahrzeit bei oder un-
ter Halbgas (Sorgfältig den Motorbetrie-
büberprüfen.)
MISE EN MARCHE ET RODAGE
ANLASSEN UND EINFAHREN
PROCEDURE DE RODAGE
1. Avant de mettre le moteur en marche, faire le
plein d’essence.
2. Effectuer les contrôles avant utilisation de la
machine.
3. Lancer le moteur et le laisser se réchauffer.
Vérifier le régime de ralenti, le fonctionne-
ment des commandes et l’efficacité du bouton
d’arrêt du moteur “ENGINE STOP”. Remettre
ensuite le moteur en marche et vérifier son
fonctionnement dans les 5 minutes maximum.
4. Piloter la machine sur les rapports inférieurs
et à régime modéré durant les cinq à huit pre-
mières minutes. S’arrêter et vérifier l’état de
la bougie; elle devrait donner des indices de
richesse durant le rodage.
5. Vérifier le fonctionnement du moteur à une
ouverture des gaz de 1/4 à 1/2 (petite à
moyenne vitesse) pendant environ 1 heure.
6. Remettre le moteur en marche et vérifier son
fonctionnement à tous les régimes. Arrêter et
vérifier la bougie. Relancer le moteur et pilo-
ter la machine pendant 10 à 15 minutes sup-
plémentaires. Elle sera alors prête pour la
course.
ATTENTION:
Après le rodage ou avant chaque course, il
faut vérifier toutes les fixations et serrages
comme indiqué dans “POINTS DE VERIFI-
CATION DE COUPLE DE SERRAGE”.
Serrer toutes ces fixations comme requis.
Après avoir remplacé les pièces suivantes, un
nouveau rodage est nécessaire.
CYLINDRE ET VILEBREQUIN:
Une heure environ de rodage est nécessaire.
PISTONS, SEGMENTS, SOUPAPES, ARBRES
A CAMES:
Ces pièces nécessitent un rodage de 30 minutes
environ à une ouverture des gaz de maximum
1/2. Surveiller attentivement l’état du moteur
pendant la marche.
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GEN
INFO
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TORQUE-CHECK POINTS
TORQUE-CHECK POINTS
NOTE:
Concerning the tightening torque, refer to
“MAINTENANCE SPECIFICATIONS” section
in the CHAPTER 2.
Frame to rear frame
Fuel tank to frame
Silencer to rear frame
Frame to engine
Engine bracket to engine
Engine bracket to frame
Steering shaft to frame
Steering shaft to handle crown
Handle crown to handlebar
Front fork to handle crown
Front fork to under bracket
Assembly of links
Link to frame
Link to shock absorber
Link to swingarm
Shock absorber to frame
Tightening of pivot shaft
Tightening of front axle
Tightening of axle holder
Tightening of rear axle
Wheel to sprocket
Caliper to front fork
Brake disc to wheel
Tightening of union bolt
Master cylinder to handleber
Tightening of air bleeder
Brake pedal to frame
Brake disc to wheel
Tightening of union bolt
Master cylinder to frame
Tightening of air bleeder
Fuel tank to fuel cock Frame construction
Combined seat and tank
Exhaust system
Engine mounting
Steering Steering shaft to
handlebar
Suspension Front Steering shaft to front
fork
Rear For link type
Rear Installation of shock
absorber
Rear Installation of swing-
arm
Wheel Installation of wheel Front
Rear
Brake Front
Rear
Fuel system