Spark plug YAMAHA WR 250F 2007 User Guide

4 - 15
TUNSETTING
Examples of carburetor setting depending on symptom
This should be taken simply for an example. It is necessary to set the carburetor while checking the operating condi-
tions of the engine.Symptom Setting Checking
At full throttle
Hard breathing
Shearing noise
Whitish spark plug
↓
Lean mixtureIncrease main jet calibration no.
(Gradually)Discoloration of spark plug
→
If tan color, it is in good condition.
If cannot be corrected:
Clogged float valve seat
Clogged fuel hose
Clogged fuel cock
Check that the accelerator pump operates
smoothly.
At full throttle
Speed pick-up stops
Slow speed pick-up
Slow response
Sooty spark plug
↓
Rich mixtureDecrease main jet calibration no.
(Gradually)Discoloration of spark plug
→
If tan color, it is in good condition.
If cannot be corrected:
Clogged air filter
Fuel overflow from carburetor
Lean mixture Lower jet needle clip position.
(1 groove down)
The clip position is the jet needle groove
on which the clip is installed. The positions
are numbered from the top.
Check that the accelerator pump operates
smoothly. (except for rich mixture
symptom). Rich mixture Raise jet needle clip position.
(1 groove up)
1/4 ~ 3/4 throttle
Hard breathing
Lack of speedLower jet needle clip position.
(1 groove down)
1/4 ~ 1/2 throttle
Slow speed pick-up
Poor accelerationRaise jet needle clip position.
(1 groove up)
Closed to 1/4 throttle
Hard breathing
Speed downUse jet needle with a smaller diameter. Slow-speed-circuit passage
Clogged
→ Clean.
Overflow from carburetor
Closed to 1/4 throttle
Poor accelerationUse jet needle with a larger diameter.
Raise jet needle clip position.
(1 groove up)
Poor response in the low to
intermediate speedsRaise jet needle clip position.
If this has no effect, lower the jet needle
clip position.
Poor response when throttle is
opened quicklyCheck overall settings.
Use main jet with a lower calibration no.
Raise jet needle clip position.
(1 groove up)
If these have no effect, use a main jet with
a higher calibration no. and lower the jet
needle clip position.Check air filter for fouling.
Check that the accelerator pump operates
smoothly.
Leaner
↑
(Standard)
↓
Richer
Jet needleClip
Groove 7 Groove 6
Groove 5
Groove 4
Groove 3
Groove 2
Groove 1
*

5 - 45
ENGCAMSHAFTS
CAMSHAFTS
CYLINDER HEAD COVER
Extent of removal:
1 Cylinder head cover removal
Extent of removal Order Part name Q’ty Remarks
CYLINDER HEAD COVER REMOVAL
Preparation for removal Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE COVERS”
section in the CHAPTER 3.
Air cut-off valve assembly Refer to “AIR INDUCTION SYSTEM” section.
1 Spark plug 1
2 Cylinder head breather hose 1
3 Bolt (cylinder head cover) 2
4 Cylinder head cover 1
5 Cylinder head cover gasket 1
6 Timing chain guide (top side) 1
1

5 - 65
ENGCAMSHAFTS
7. Install:
Cylinder head breather hose
Spark plug
T R..13 Nm (1.3 m · kg, 9.4 ft · lb)
7. Monter:
Durit de mise à l’air de la culasse
Bougie
T R..13 Nm (1,3 m · kg, 9,4 ft · lb)
ARBRES A CAMES

5 - 71
ENGCYLINDER HEAD
INSPECTION
Cylinder head
1. Eliminate:
Carbon deposits
(from the combustion cham-
bers)
Use a rounded scraper.
NOTE:Do not use a sharp instrument to
avoid damaging or scratching:
Spark plug threads
Valve seats
2. Inspect:
Cylinder head
Scratches/damage
→
Replace.
3. Measure:
Cylinder head warpage
Out of specification
→ Resur-
face.
Cylinder head warpage:
Less than 0.05 mm
(0.002 in)
Warpage measurement and
resurfacing steps:
Place a straightedge and a
feeler gauge across the cylinder
head.
Use a feeler gauge to measure
the warpage.
If the warpage is out of specifi-
cation, resurface the cylinder
head.
Place a 400 ~ 600 grit wet
sandpaper on the surface plate,
and resurface the head using a
figure-eight sanding pattern.
NOTE:To ensure an even surface rotate
the cylinder head several times.
ASSEMBLY AND INSTALLATION
Cylinder head
1. Install:
Dowel pin
1
Cylinder head gasket
2
Timing chain guide
(exhaust side)
3
Cylinder head
4
NOTE:While pulling up the timing chain,
install the timing chain guide
(exhaust side) and cylinder head.
New
CONTROLE
Culasse
1. Eliminer:
Dépôts de calamine
(des chambres de combustion)
Utiliser un grattoir arrondi.
N.B.:
Ne pas utiliser d’instrument pointu pour
éviter d’endommager ou de griffer:
Filets de bougie
Sièges de soupapes
2. Contrôler:
Culasse
Rayures/endommagement →
Remplacer.
3. Mesurer:
Déformation de la culasse
Hors spécifications → Rectifier.
Déformation de la culasse:
Inférieure à 0,05 mm
(0,002 in)
Etapes de la mesure de la limite de
déformation et de la rectification:
Placer un réglet et une jauge
d’épaisseur à lames sur la culasse.
Utiliser une jauge d’épaisseur à
lames pour mesurer la déforma-
tion.
Si la déformation est hors spécifi-
cations, rectifier la culasse.
Placer un morceau de papier émeri
humide 400 à 600 sur le marbre et
rectifier la culasse en décrivant des
“huit”.
N.B.:
Pour obtenir une surface régulière,
tourner la culasse à plusieurs reprises.
ASSEMBLAGE ET MONTAGE
Culasse
1. Monter:
Goujon 1
Joint de culasse 2
Patin de chaîne de distribution
(côté échappement) 3
Culasse 4
N.B.:
Tout en soulevant la chaîne de distribu-
tion, monter le patin de chaîne de distri-
bution (côté échappement) et la culasse.
New
CULASSE

7 - 1
–+ELECELECTRICAL COMPONENTS AND WIRING DIAGRAM
EC600000
ELECTRICAL
NOTE:This section is intended for those who have basic knowledge and skill concerning the servicing of Yamaha motorcycles
(e.g., Yamaha dealers, service engineers, etc.) Those who have little knowledge and skill concerning servicing are
requested not to undertake inspection, adjustment, disassembly, or reassembly only by reference to this manual. It may
lead to servicing trouble and mechanical damage.
EC610000
ELECTRICAL COMPONENTS AND WIRING DIAGRAM
EC611000ELECTRICAL COMPONENTS
1Headlight
2Multi-function display
3Engine stop switch
4Clutch switch
5Diode
6Starter relay diode7Throttle position sensor
8Starter relay
9Fuse
0Starting circuit cut-off relay
ACDI unit
BTaillightCNeutral switch
DStarter motor
EAC magneto
FRectifier/regulator
GIgnition coil
HSpark plugIStart switch
JMain switch
KSpeed sensor
LBattery

7 - 3
–+ELECELECTRICAL COMPONENTS AND WIRING DIAGRAM
EC612000WIRING DIAGRAM
1Headlight
2Multi-function display
3Engine stop switch
4Clutch switch
5Diode
6Starter relay diode
7Throttle position sensor
8Starter relay
9Fuse
0Starting circuit cut-off relay
ACDI unitBTaillight
CNeutral switch
DStarter motor
EAC magneto
FRectifier/regulator
GIgnition coil
HSpark plug
IStart switch
JMain switch
KSpeed sensor
LBatteryCOLOR CODE
B ...................... Black
Br ..................... Brown
Ch .................... Chocolate
Dg .................... Dark green
G...................... Green
Gy .................... Gray
L ...................... Blue
O...................... Orange
R ...................... RedSb .................... Sky blue
W ..................... White
Y ...................... Yellow
B/L ................... Black/Blue
B/W .................. Black/White
L/B ................... Blue/Black
L/R ................... Blue/Red
L/Y ................... Blue/Yellow
L/W .................. Blue/White
R/B................... Red/Black
R/W.................. Red/White

7 - 5
–+ELECIGNITION SYSTEM
EC620000
IGNITION SYSTEM
INSPECTION STEPS
Use the following steps for checking the possibility of the malfunctioning engine being attributable to ignition system failure
and for checking the spark plug which will not spark.
*1 marked: Refer to “FUSE INSPECTION” section in the CHAPTER 3.
*2 marked: Refer to “BATTERY INSPECTION AND CHARGING” section in the CHAPTER 3.
*3 marked: Only when the ignition checker is used.
NOTE:•Remove the following parts before inspection.
1) Seat
2) Fuel tank
•Use the following special tools in this inspection.
*1 Check fuse.Replace fuse and check
wire harness.
*2 Check battery. Recharge or replace.
Spark gap test*3 Clean or replace spark
plug.
Check entire ignition system for
connection.
(couplers, leads and ignition coil)Repair or replace.
Check engine stop switch. Replace.
Check main switch.Replace.
Check ignition coil. Primary coil Replace.
Secondary coil Replace.
Check AC magneto. Pickup coil Replace.
Check neutral switch. Repair or replace.
Replace CDI unit.
Dynamic spark tester:
YM-34487
Ignition checker:
90890-06754
Pocket tester:
YU-3112-C/
90890-03112
No good
OK
No good
OK
Spark
No spark
No good
OK
No good
OK
No good
OK
No good
OKNo good
No good
OK
No good
OK

7 - 11
–+ELECIGNITION SYSTEM
SPARK GAP TEST
1. Disconnect the ignition coil from
spark plug.
2. Remove the ignition coil cap.
3. Connect the dynamic spark
tester
1 (ignition checker
2) as
shown.
•Ignition coil
3
•Spark plug
4
ÈFor USA and CDN
ÉExcept for USA and CDN
4. Kick the kickstarter crank.
5. Check the ignition spark gap.
6. Start engine, and increase spark
gap until misfire occurs. (for USA
and CDN only)
Minimum spark gap:
6.0 mm (0.24 in)
È
É
COUPLERS, LEADS AND
IGNITION COIL CONNECTION
INSPECTION
1. Check:
•Couplers and leads connec-
tion
Rust/dust/looseness/short-cir-
cuit
→ Repair or replace.
•Ignition coil and spark plug as
they are fitted
Push in the ignition coil until it
closely contacts the spark plug
hole in the cylinder head
cover.
ENGINE STOP SWITCH
INSPECTION
1. Inspect:
•Engine stop switch conduct
No continuity while being pushed
→
Replace.
Continuity while being freed
→
Replace.Tester (+) lead →
Black lead 1

Tester (–) lead →
Black lead 2

B
1
B
2
Tester
selector
position
PUSH IN
Ω
×
1
FREE
TEST DE LA LONGUEUR
D’ETINCELLE
1. Déconnecter la bobine d’allumage
de la bougie.
2. Déposer le capuchon de la bobine
d’allumage.
3. Connecter le testeur dynamique
d’étincelle 1 (contrôleur d’allu-
mage 2) comme indiqué.
Bobine d’allumage 3
Bougie 4
È
USA et CDN
É
Sauf USA et CDN
4. Actionner le kick.
5. Contrôler la longueur d’étincelle
d’allumage.
6. Démarrer le moteur et augmenter la
longueur d’étincelle jusqu’à ce
qu’un raté se produise. (uniquement
USA et CDN)
Longueur d’étincelle
minimum:
6,0 mm (0,24 in)
CONTROLE DES CONNEXIONS
DES FICHES RAPIDES, DES FILS
ET DE LA BOBINE D’ALLUMAGE
1. Vérifier:
Connexion des coupleurs et des
fils
Rouille/poussière/jeu/court-cir-
cuit → Réparer ou remplacer.
Bobine d’allumage et bougie en
place
Appuyer sur la bobine d’allu-
mage jusqu’à ce qu’elle soit en
contact étroit avec le trou de bou-
gie du couvre-culasse.
CONTROLE DU COUPE-CIRCUIT
DU MOTEUR
1. Contrôler:
Continuité du coupe-circuit du
moteur
Pas de continuité lorsque enfoncé →
Remplacer.
Continuité lorsque relâché → Rempla-
cer.Fil (+) du multimètre → fil noir 1
Fil (–) du multimètre → fil noir 2
B
1 B
2 Position du
sélecteur du
multimètre
ENFONCE
Ω × 1
RELACHE
SYSTEME D’ALLUMAGE

7 - 15
–+ELECIGNITION SYSTEM
EC626002IGNITION COIL INSPECTION
1. Remove the ignition coil cap.
2. Inspect:
•Primary coil resistance
Out of specification
→
Replace.
Tester (+) lead →
Orange lead 1

Tester (–) lead →
Black lead 2

Primary coil
resistanceTester
selector
position
0.08 ~ 0.10 Ω

at 20 °C (68 °F)Ω
×
1
3. Inspect:
•Secondary coil resistance
Out of specification
→
Replace.
Tester (+) lead →
Orange lead 1

Tester (–) lead →

Spark plug terminal 2
Secondary
coil resistanceTester
selector
position
4.6 ~ 6.8 kΩ
at
20 °C (68 °F)kΩ
×
1
4. Inspect:
•Sealed portion of ignition coil
a
•Spark plug terminal pin
b
•Threaded portion of spark plug
c
Wear
→ Replace.
CONTROLE DE LA BOBINE
D’ALLUMAGE
1. Déposer le capuchon de la bobine
d’allumage.
2. Contrôler:
Résistance de l’enroulement pri-
maire
Hors spécifications → Rempla-
cer.
Fil (+) du multimètre →
fil orange 1
Fil (–) du multimètre → fil noir 2
Résistance de
l’enroulement
primairePosition du
sélecteur du
multimètre
0,08 à 0,10 Ω à
20 °C (68 °F)Ω × 1
3. Contrôler:
Résistance de l’enroulement
secondaire
Hors spécifications → Rempla-
cer.
Fil (+) du multimètre →
fil orange 1
Fil (–) du multimètre →
Borne de bougie 2
Résistance de
l’enroulement
secondairePosition du
sélecteur du
multimètre
4,6 à 6,8 kΩ à
20 °C (68 °F)kΩ × 1
4. Contrôler:
Partie scellée de la bobine d’allu-
mage a
Broche de la borne de bougie b
Partie filetée de la bougie c
Usure → Remplacer.
SYSTEME D’ALLUMAGE