2002 YAMAHA YZ426F engine

–+ELEC

SYSTEME D’ALLUMAGE
ZÜNDANLAGE
ZÜNDFUNKENSTRECKE KONTROLLIEREN
1. Den Zündkerzenstecker von der Zünd-
kerze abziehen.
2. Den Zündfunkenstreckentester
1
(bzw.
2
) wie abgebildet anschließen.

Zündkerzenstecker
3


Zündkerze
4

Å
Nur USA und CAN
ı
Nicht USA und CAN
3. Den Motor mit dem Kickstarter durchdre-
hen.
4. Die Zündfunkenstrecke kontrollieren.
5. Den Motor anlassen und die Zündfunken-
strecke vergrößern, bis es zu Fehlzün-
dungen kommt (nur USA und CAN).
Min. Zündfunkenstrecke
6,0 mm
MOTORSTOPPSCHALTER “ENGINE
STOP” KONTROLLIEREN
1. Kontrollieren:


Motorstoppschalter
(auf Durchgang)
Kein Durchgang bei gedrücktem Schalter
→
Erneuern.
Durchgang bei freigelassenem Schalter
→
Erneuern.
Meßkabel (+)
→
schwarz/weiß
1

Meßkabel (–)
→
schwarz
2

B/W
1
B
2
Meßgerät-
Einstellung
GE-
DRÜCK
Ω × 1
FREI
TEST DE L’INTERVALLE
D’ETINCELLEMENT D’ALLUMAGE
1. Déconnecter le capuchon de bougie de la
bougie.
2. Connecter le testeur dynamique d’étincelle
1 (testeur d’allumage 2) comme indiqué.
Capuchon de bougie 3
Bougie 4
ÅPour les E.-U. et le Canada
ıExcepté pour les E.-U. et le Canada
3. Actionner le démarreur au pied.
4. Contrôler la longueur d’étincelle d’allumage.
5. Démarrer le moteur et augmenter la longueur
d’étincelle jusqu’à ce qu’un raté se produise.
(uniquement E.-U. et Canada)
Longueur d’étincelle minimum:
6,0 mm (0,24 in)
CONTROLE DES CONNEXIONS DE
COUPLEURS ET FILS
1. Contrôler:
Connexion de coupleurs et fils
Rouille/poussière/jeu/court-circuit →
Réparer ou changer.
CONTROLE DU BOUTON D’ARRET DU
MOTEUR “ENGINE STOP”
1. Vérifier:
Continuité du bouton d’arrêt du moteur
“ENGINE STOP”
Pas de continuité lorsqu’enfoncé → Changer.
Continuité lorsque relâché → Changer. Fil (+) de testeur → Fil noir/blanc 1
Fil (–) de testeur → Fil noir 2
B/W
1 B
2 Position de
sélecteur de
testeur
EN-
FONCE
Ω × 1
RE-
LACHE
6 - 4
STECKVERBINDER- UND KABEL-
ANSCHLÜSSE KONTROLLIEREN
1. Kontrollieren:
Steckverbinder- und Kabelanschlüsse
Rost/Staub/Lockerheit/Kurzschluß →
Instand setzen oder erneuern.

–+ELEC
6 - 7
TPS (THROTTLE POSITION SENSOR) SYSTEM
EC690000
TPS (THROTTLE POSITION SENSOR) SYSTEM
INSPECTION STEPS
If the TPS will not operate, use the following inspection steps.
*marked: Refer to “IGNITION SYSTEM” section.
NOTE:
Use the following special tools in this inspection.
Pocket tester:
YU-3112-C/90890-03112Inductive tachometer:
YU-8036-B
Engine tachometer:
90890-03113
Check entire ignition
system for connection.Repair or replace.
Check TPS. TPS coil Replace.
*Check CDI magneto. Source coil Replace.
Check CDI unit.TPS input
voltageReplace.
OK
OK
OK
No good
No good
No good
No good

6 - 8
–+ELECTPS (THROTTLE POSITION SENSOR) SYSTEM
HANDLING NOTE
CAUTION:
Do not loosen the screws {TPS (throttle
position sensor)} 1 except when changing
the TPS (throttle position sensor) due to
failure because it will cause a drop in
engine performance.
EC624000
COUPLERS AND LEADS CONNECTION
INSPECTION
1. Check:
Couplers and leads connection
Rust/dust/looseness/short-circuit →
Repair or replace.
TPS COIL INSPECTION
1. Inspect:
TPS coil resistance
Out of specification → Replace.
2. Loosen:
Throttle stop screw 1
NOTE:
Turn out the throttle stop screw until the throt-
tle shaft is in the full close position.Tester (+) lead → Blue lead 1
Tester (–) lead → Black lead 2
TPS coil
resistanceTester selector
position
4 ~ 6 kΩ at
20 ˚C (68 ˚F)kΩ × 1

6 - 10
–+ELECTPS (THROTTLE POSITION SENSOR) SYSTEM
4. Adjust:
Idle speed
5. Insert the thin electric conductors 2
(lead) into the TPS coupler 1, as shown,
and connect the tester to them.
CAUTION:
Do not insert the electric conductors
more than required because it may
reduce the waterproof function of the
coupler.
Make sure that a short-circuit does not
develop between the terminals because it
may cause damage to electrical compo-
nents.
6. Start the engine.
7. Adjust:
TPS output voltage Adjustment steps:
Attach the inductive tachometer (engine
tachometer) to the high tension cord.
Turn the throttle stop screw 1 until the
specified idle speed.
Refer to “IDLE SPEED ADJUSTMENT”
section in the CHAPTER 3.
Idle speed:
1,700 ~ 1,900 r/min
Tester (+) lead → Yellow lead 3
Tester (–) lead → Black lead 4
Adjustment steps:
Adjust the installation angle of the TPS 1
to obtain the specified output voltage.
NOTE:
Measure the output voltage accurately with a
digital electronic voltmeter that gives an easy
reading of a small voltage.
TPS output
voltageTester selector
position
0.58 ~ 0.78 V DCV

6 - 11
–+ELECTPS (THROTTLE POSITION SENSOR) SYSTEM
8. Tighten:
Screw (TPS) 1
9. Stop the engine.
EC694000
TPS INPUT VOLTAGE INSPECTION
1. Disconnect the TPS coupler.
2. Start the engine.
3. Inspect:
TPS input voltage
Out of specification → Replace the CDI
unit.
Tester (+) lead → Blue lead 1
Tester (–) lead → Black/Blue lead 2
TPS input
voltageTester selector
position
4 ~ 6 V DCV-20

7 - 1
TUN

EC700000
TUNING
EC710000
ENGINE
Carburetor setting

The air/fuel mixture will vary depending on
atmospheric conditions. Therefore, it is nec-
essary to take into consideration the air pres-
sure, ambient temperature, humidity, etc.,
when adjusting the carburetor.

Perform a test run to check for proper engine
performance (e.g., throttle response) and
spark plug(-s) discoloration or fouling. Use
these readings to determine the best possi-
ble carburetor setting.
NOTE:

It is recommended to keep a record of all car-
buretor settings and external conditions (e.g.,
atmospheric conditions, track/surface condi-
tions, lap times) to make future carburetor set-
ting easier.
WARNING


The carburetor is a part of the fuel line.
Therefore, be sure to install it in a well-
ventilated area, away from flammable
objects and any sources of fire.

Never look into the carburetor intake.
Flames may shoot out from the pipe if the
engine backfires while it is being started.
Gasoline may be discharged from the
accelerator pump nozzle when the carbu-
retor has been removed.
SETTING

7 - 2
TUN
CAUTION:


The carburetor is extremely sensitive to
foreign matter (dirt, sand, water, etc.).
During installation, do not allow foreign
matter to get into the carburetor.

Always handle the carburetor and its
components carefully. Even slight
scratches, bends or damage to carbure-
tor parts may prevent the carburetor from
functioning correctly. Carefully perform
all servicing with the appropriate tools
and without applying excessive force.

When the engine is stopped or when
riding at no load, do not open and close
the throttle unnecessarily. Otherwise, too
much fuel may be discharged, starting
may become difficult or the engine may
not run well.

After installing the carburetor, check that
the throttle operates correctly and opens
and closes smoothly.
Atmospheric conditions and carburetor
settings
The air density (i.e., concentration of oxygen
in the air) determines the richness or lean-
ness of the air/fuel mixture. Therefore, refer
to the above table for mixture settings.
That is:

Higher temperature expands the air with its
resultant reduced density.

Higher humidity reduces the amount of oxy-
gen in the air by so much of the water vapor
in the same air.

Lower atmospheric pressure (at a high alti-
tude) reduces the density of the air.
Air temp. HumidityAir
pressure
(altitude)Mixture Setting
High High Low (high) Richer Leaner
Low Low High (low) Leaner Richer
SETTING

7 - 4
TUN

SETTING
Pilot system
The FLATCR carburetor is manufactured with
a pilot screw. The pilot screw adjustment
ranges from fully closed throttle to 1/4 open
throttle.
Main jet adjustment
The richness of the air-fuel mixture at full throt-
tle can be set by changing the main jet
1
.
If the air-fuel mixture is too rich or too lean, the
engine power will drop, resulting in poor accel-
eration.
Effects of changing the main jet (reference)
Å
Idle
ı
Fully open
Standard main jet #162
1/4 1/2 3/4
+10%
#162
–10%
#172
#152
Åı