2002 YAMAHA YZ250F stop start

3 - 12
INSP
ADJ
AIR FILTER CLEANING
2. Adjust:
Decompression 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.
1. Remove:
Seat
Fitting bolt 1
Washer 2
Air filter element 3
Air filter guide 4
2. Clean:
Air filter element
Clean them with solvent.
NOTE:
After cleaning, remove the remaining solvent
by squeezing the element.
CAUTION:
Do not twist the element when squeezing
the element.
Leaving too much of solvent in the ele-
ment may result in poor starting. Adjustment steps:
Loosen the locknut 1.
Turn the adjuster 2 in or out until the
adjustment is suitable.
Tighten the locknut.
CAUTION:
After the adjustment, start the engine
and make sure that the engine does not
stop when the handlebar is turned fully
both ways. If the decompression cable is
too tense, the engine will stop by the
decompression system.

3 - 19
INSP
ADJ
ENGINE IDLING SPEED ADJUSTMENT
1. Start the engine and thoroughly warm it
up.
2. Attach:
Inductive tachometer
To spark plug lead.
3. Adjust:
Engine idling speed
Adjustment steps:
Adjust the pilot screw.
Refer to “PILOT SCREW ADJUSTMENT”
section.
Turn the throttle stop screw 1 until the
engine runs at the lowest possible speed.
To increase idle speed → Turn the throt-
tle stop screw 1 in a.
To decrease idle speed → Turn the throt-
tle stop screw 1 out b.
Inductive tachometer:
YU-8036-B
Engine tachometer:
90890-03113
Engine idling speed:
1,900 ~ 2,100 r/min
VALVE CLEARANCE INSPECTION AND
ADJUSTMENT
NOTE:
The valve clearance should be adjusted
when the engine is cool to the touch.
The piston must be at Top Dead Center
(T.D.C.) on compression stroke to check or
adjust the valve clearance.
1. Remove:
Seat
Fuel tank
Refer to “SEAT, FUEL TANK AND
SIDE COVERS” section in the CHAP-
TER 4.
2. Drain:
Coolant
Refer to “COOLANT REPLACEMENT”
section.
ENGINE IDLING SPEED ADJUSTMENT/
VALVE CLEARANCE INSPECTION AND ADJUSTMENT

4 - 15
ENGCARBURETOR
8. Install:
Throttle shaft assembly 1
Washer (metal) 2
Washer (resin) 3
Valve lever 4
NOTE:
Apply the fluorochemical grease on the bear-
ings.
Fit the projection a on the throttle shaft
assembly into the slot b in the throttle posi-
tion sensor.
Make sure the stopper c of the spring fits
into the recess in the carburetor.
Turn the throttle shaft assembly left while
holding down the lever 1 5 and fit the throt-
tle stop screw tip d to the stopper e of the
throttle shaft assembly pulley.
ab
1
2
3
4
c
e
d
5
9. Install:
Push rod 1
NOTE:
While holding down the lever 1 2, insert the
push rod farthest into the carburetor.12
10. Install:
Starter jet 1
Pilot jet 2
Spacer 3
Needle jet 4
Main jet 5

6 - 4
–+ELEC

IGNITION SYSTEM
SPARK GAP TEST
1. Disconnect the spark plug cap from spark
plug.
2. Connect the dynamic spark tester
1
(ignition checker
2
) as shown.

Spark plug cap
3


Spark plug
4

Å
For USA and CDN
ı
Except for USA and CDN
3. Kick the kickstarter crank.
4. Check the ignition spark gap.
5. Start engine, and increase spark gap until
misfire occurs. (for USA and CDN only)
Minimum spark gap:
6.0 mm (0.24 in)
Å
ı

EC624000
COUPLERS AND LEADS CONNECTION
INSPECTION
1. Check:

Couplers and leads connection
Rust/dust/looseness/short-circuit
→

Repair or replace.
ENGINE STOP SWITCH INSPECTION
1. Inspect:

Engine stop switch conduct
No continuous while being pushed
→
Replace.
Continuous while being freed
→
Replace.
Tester (+) lead
→
Black/White lead
1

Tester (–) lead
→
Black lead
2

B/W
1
B
2
Tester selec-
tor position
PUSH IN
Ω

×
1
FREE

–+ELEC

SYSTEME D’ALLUMAGE
ZÜNDANLAGE
IMPIANTO DI ACCENSIONE
ZÜNDFUNKENSTRECKE KON-
TROLLIEREN
1. Den Zündkerzenstecker von
der Zündkerze abziehen.
2. Den Zündfunkenstreckente-
ster
1 (bzw. 2) wie abgebil-
det anschließen.
Zündkerzenstecker 3
Zündkerze 4
ÅNur USA und CDN
ıNicht USA und CDN
3.Den Motor mit dem Kick-
starter durchdrehen
.
4. Die Zündfunkenstrecke kon-
trollieren.
5. Den Motor anlassen und die
Zündfunkenstrecke vergrö-
ßern, bis es zu Fehlzündun-
gen kommt (nur USA und
CDN).
Min. Zündfunkenstrecke
6,0 mm
STECKVERBINDER- UND KABEL-
ANSCHLÜSSE KONTROLLIEREN
1. Kontrollieren:
Steckverbinder- und Kabel-
anschlüsse
Rost/Staub/Lockerheit/Kurz-
schluß → Instand setzen
oder erneuern.
MOTORSTOPPSCHALTER
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 Meßge-
rät-
Einstel-
GE-
DRÜCKT
Ω × 1
FREI
TEST DE LA LONGUEUR D’ETIN-
CELLE D’ALLUMAGE
1. Déconnecter le capuchon de bou-
gie de la bougie.
2. Connecter le testeur dynamique
d’étincelle 1 (testeur d’allu-
mage 2) comme indiqué.
Capuchon de bougie 3
Bougie 4
ÅPour les USA et le CDN
ıExcepté pour les USA et le CDN
3. Actionner le kick.
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. (unique-
ment USA et CDN)
Longueur d’étincelle mini-
mum:
6,0 mm (0,24 in)
CONTROLE DES CONNEXIONS
DE COUPLEURS ET FILS
1. Contrôler:
Connexion de coupleurs et fils
Rouille/poussière/jeu/court-cir-
cuit → Réparer ou Remplacer.
CONTROLE DU COUPE-CIRCUIT
DU MOTEUR
1. Vérifier:
Continuité du coupe-circuit du
moteur
Pas de continuité lorsqu’enfoncé →
Remplacer.
Continuité lorsque relâché → Rempla-
cer.Fil (+) de multimètre →
Fil noir/blanc 1
Fil (–) de multimètre →
Fil noir 2
B/W
1B
2Position de
sélecteur
du multi-
mètre
EN-
FONCE
Ω × 1
RE-
LACHE
6 - 4
Test della distanza tra gli elettrodi
1. Staccare il cappuccio della can-
dela.
2. Collegare il tester della dinami-
cità della scintilla 1 (tester
dell’accensione 2) come illu-
strato.
Cappuccio della candela 3
Candela 4
ÅPer USA e CDN
ı Tranne USA e CDN
3. Agire sulla pedivella di avvia-
mento.
4. Controllare la distanza tra gli
elettrodi.
5. Avviare il motore ed aumentare
la distanza tra gli elettrodi fino a
che non si verifica uno scatto a
vuoto. (Solo per USA e CDN)
Distanza minima tra gli
elettrodi:
6,0 mm (0,24 in)
ISPEZIONE DEI COLLEGAMENTI
DEGLI ACCOPPIATORI E DEI
CAVI
1. Controllare:
Collegamento degli accoppia-
tori e dei cavi
Ruggine/polvere/allentamento/
cortocircuito → Riparare o
sostituire.
ISPEZIONE DELL’INTERRUT-
TORE DI ARRESTO DEL MOTORE
1. Ispezionare:
Conduzione interruttore di
arresto motore
Assenza di continuità se premuto →
Sostituire.
Continuità se rilasciato→ Sostituire. Conduttore (+) del tester →
Conduttore nero/bianco 1
Conduttore (–) del tester →
Conduttore nero 2
B/W
1B
2Posizione
selettore
tester
PRE-
MUTO
Ω × 1
RILA-
SCIATO

6 - 11
–+ELEC
9. Tighten:
Screw (throttle position sensor) 1
NOTE:
Tighten the screws (throttle position sensor)
using the T20 bit (tamper resistant fastener
type).
10. Stop the engine.
THROTTLE POSITION SENSOR INPUT
VOLTAGE INSPECTION
1. Disconnect the throttle position sensor
coupler.
2. Start the engine.
3. Inspect:
Throttle position sensor input voltage
Out of specification → Replace the CDI
unit.
Tester (+) lead → Blue lead 1
Tester (–) lead → Black/Blue lead 2
Throttle posi-
tion sensor
input voltageTester selector
position
4 ~ 6 V DCV-20
THROTTLE POSITION SENSOR SYSTEM

–+ELEC
9. Festziehen:
Schraube (Drosselklappen-
positionssensor) 1
HINWEIS:
Die Schrauben (Drosselklappenposi-
tionssensor) mit dem T20 Bit (ver-
stellfeste Befestigung) lösen.
10. Den Motor stoppen.
PRÜFEN DER TPS-EINGANGS-
SPANNUNG
1. Die Drosselklappenpositions-
sensor-Steckverbindung tren-
nen.
2. Den Motor starten.
3. Prüfen:
Drosselklappenpositionssen-
sor-Eingangsspannung
Außerhalb des Sollwerts →
Die CDI-Einheit austau-
schen.
Prüfgerätkabel (+) →
Blaues Kabel 1
Prüfgerätkabel (–) →
Schwarzes Kabel 2
Drosselklap-
penpositions-
sensor-
Eingangsspan-Prüfgeräte-
instellung
4–6 V DCV-20
9. Serrer:
Vis (capteur de papillon des
gaz) 1
N.B.:
Desserrer les vis (capteur de papillon des
gaz) à l’aide d’un embout T20 (pour vis
de type intraficable).
10. Arrêter le moteur.
CONTROLE DE LA TENSION
D’ENTREE DU CAPTEUR DE
PAPILLON DES GAZ
1. Débrancher la fiche rapide du
capteur de papillon des gaz.
2. Démarrer le moteur.
3. Contrôler:
Tension d’entrée du capteur de
papillon des gaz
Hors spécifications → Rempla-
cer le bloc CDI.
Fil (+) de multinètre → Fil bleu 1
Fil (–) de multinètre → Fil noir 2
Tension d’entrée
du capteur de
papillon des gaz Position du
sélecteur de
multinètre
4 à 6 V DCV-20
9. Serrare:
Vite (sensore di posizione della
valvola a farfalla) 1
NOTA:
Avvitare le viti (sensore di posizione
della valvola a farfalla) utilizzando la
punta T20 (tipo dispositivo di fissaggio
resistente alla manomissione).
10. Fermare il motore.
ISPEZIONE TENSIONE DI
INGRESSO SENSORE DELLA
POSIZIONE DELLA VALVOLA A
FARFALLA
1. Scollegare l’accoppiatore del sen-
sore di posizione della valvola a
farfalla.
2. Avviare il motore.
3. Ispezionare:
Tensione di ingresso sensore di
posizione della valvola a far-
falla
Fuori specifica → Sostituire
l’unità CDI.
Conduttore (+) del tester →
Conduttore blu 1
Conduttore (–) del tester →
Conduttore nero 2
Tensione di
ingresso sensore
di posizione della
valvola a farfallaPosizione
selettore
tester
4 ~ 6 V DCV-20
6 - 11
CIRCUIT DU CAPTEUR DE PAPILLON DES GAZ
DROSSELKLAPPEN-POSITIONSSENSOR
SISTEMA SENSORE DELLA POSIZIONE DELLA VALVOLA A FARFALLA

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