check engine YAMAHA WR 250F 2006 Owner's Guide

7 - 3
TUNSETTING
CAUTION:
The carburetor is extremely sen-
sitive to foreign matter (dirt,
sand, water, etc.). During instal-
lation, do not allow foreign mat-
ter to get into the carburetor.
Always handle the carburetor
and its components carefully.
Even slight scratches, bends or
damage to carburetor 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 leanness 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 den-
sity.
•Higher humidity reduces the
amount of oxygen in the air by so
much of the water vapor in the
same air.
•Lower atmospheric pressure (at a
high altitude) 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
ATTENTION:
Le carburateur est extrêmement
sensible aux corps étrangers (pous-
sière, sable, eau, etc.). Pendant le
montage, veiller à ce qu’aucun
corps étranger ne puisse pénétrer
dans le carburateur.
Toujours manipuler le carburateur
et ses composants avec prudence.
Tout endommagement (rayures
même légères, courbures, etc.) peut
empêcher le carburateur de fonc-
tionner correctement. Effectuer soi-
gneusement tout entretien à l’aide
des outils adéquats et sans forcer.
Lorsque le moteur est arrêté, ou
tourne sans charge, ne pas ouvrir et
fermer inutilement les gaz. Cela ris-
querait d’amener trop de carburant
et de rendre le démarrage difficile
ou d’altérer le fonctionnement du
moteur.
Après avoir monté le carburateur,
contrôler que le papillon fonctionne
correctement et s’ouvre et se ferme
sans problème.
Conditions atmosphériques et réglages
du carburateur
La densité de l’air (c.-à-d. la concen-
tration d’oxygène dans l’air) déter-
mine la richesse ou la pauvreté du
mélange air/carburant. Il convient dès
lors de se conformer au tableau ci-des-
sus pour la composition du mélange.
Tenir compte des trois facteurs suivants:
La température de l’air: la densité de
l’air diminue au fur et à mesure que
l’air se dilate sous l’effet des tempéra-
tures élevées.
Le taux d’humidité de l’air: le taux
d’oxygène diminue au fur et à mesure
que le taux d’humidité augmente.
Pression atmosphérique (altitude): la
densité diminue au fur et à mesure que
la pression atmosphérique descend
(altitude élevée).
Temp.
de l’airHumiditéPression
d’air
(altitude)MélangeRégla-
ges
Haute HauteBasse
(élevée)Plus
richePlus
pauvre
Basse BasseHaute
(basse)Plus
pauvrePlus
riche
REGLAGE

7 - 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
*