2006 YAMAHA BRUIN 250 engine

8-49
CAUTION:_ Never operate the engine with the air filter ele-
ment removed. This will allow unfiltered air to
enter, causing rapid engine wear and possible
engine damage. Additionally, operation with-
out the air filter element will affect carburetor
jetting with subsequent poor performance and
possible engine overheating. _
EBU00296
Carburetor adjustment
The carburetor is a vital part of the engine and re-
quires very sophisticated adjustment. Most adjust-
ing should be left to a Yamaha dealer who has the
professional knowledge and experience to do so.
However, the idling speed may be performed by
the owner as a part of the usual maintenance rou-
tine.CAUTION:
The carburetor was set at the Yamaha factory
after many tests. If the settings are disturbed
by someone without sufficient technical
knowledge, poor engine performance and
damage may result.
EE.book Page 49 Friday, May 27, 2005 5:00 PM

8-51 1. Throttle stop screw
1. Vis d’arrêt de l’accélérateur
1. Tornillo de tope del acelerador
EBU13020
Idle speed adjustmentNOTE:_ A diagnostic tachometer must be used for this pro-
cedure. _1. Start the engine and warm it up for a few min-
utes at approximately 1,000 to 2,000 r/min.
Occasionally rev the engine to 4,000 to
5,000 r/min. The engine is warm when it
quickly responds to the throttle.
2. Connect the tachometer to the spark plug
lead, and then set the idle to the specified
idling speed by adjusting the throttle stop
screw. Turn the screw in direction
a to in-
crease the engine speed, and in direction
b
to decrease the engine speed.
Specified idle speed:
1,400–1,500 r/min
EE.book Page 51 Friday, May 27, 2005 5:00 PM

8-53 1. Locknut 2. Adjusting bolt
a. Throttle lever free play
1. Contre-écrou 2. Boulon de réglage
a. Jeu du levier d’accélération
1. Contratuerca 2. Perno de ajuste
a. Juego libre de la palanca del acelerador
EBU00303
Valve clearance adjustment
The correct valve clearance changes with use, re-
sulting in improper fuel/air supply or engine noise.
To prevent this, the valve clearance must be ad-
justed regularly. This adjustment however, should
be left to a professional Yamaha service techni-
cian.
EBU00307
Throttle lever adjustmentNOTE:Adjust the engine idling speed before adjusting the
throttle lever free play.1. Loosen the locknut.
2. Turn the adjusting bolt until the throttle lever
free play is 3.0–5.0 mm.
3. Tighten the locknut.
EE.book Page 53 Friday, May 27, 2005 5:00 PM

8-77
EBU00570
Cable inspection and lubrication
WARNING
Inspect cables frequently and replace if dam-
aged. Corrosion can result when the outer cov-
ering of control cables becomes damaged.
Cables can also become frayed or kinked. Op-
eration of controls could be restricted, which
could cause an accident or injury. Lubricate the inner cables and the cable ends. If
the cables do not operate smoothly, ask a Yamaha
dealer to replace them.
Recommended lubricant:
Engine oil
EE.book Page 77 Friday, May 27, 2005 5:00 PM

8-107
EBU00440Troubleshooting chart
1. Fuel
Check if there is fuel
in the fuel tank.There is fuel.Turn the fuel cock
lever to “OFF”.
Turn the fuel cock
lever to “ON”. Remove the
fuel hose. No fuel.
Clean fuel
cock. Some fuel.Turn the fuel
cock to “RES”.Restart engine.
No fuel.Supply fuel.
2. Compression
Use electric starter to
see if there is
compression.There is compression.
Compression normal.
No compression.Ask a Yamaha dealer to
inspect.
3. Ignition
Remove spark plug and
check electrodes.
WetWipe clean with dry cloth.
DryAttach spark plug cap and
ground to chassis.Use the
electric starter.Spark good.Ignition system
normal.
Spark weak.
Adjust plug gap
or replace plug. No spark.
Ask a Yamaha dealer to
inspect. 4. Battery
Use electric starter.Engine turns over
quickly.Battery good.
Engine turns over
slowly.Check fluid, recharge,
check connections.Check fuel
flow.
Fuel cock
clogged.
EE.book Page 107 Friday, May 27, 2005 5:00 PM

9-1
EBU00420
1-CLEANING AND STORAGE
A. CLEANING
Frequent, thorough cleaning of your machine will
not only enhance its appearance but will improve
its general performance and extend the useful life
of many components.
1. Before cleaning the machine:
a. Block off the end of the exhaust pipe to pre-
vent water entry. A plastic bag and strong
rubber band may be used.
b. Make sure the spark plug and all filler caps
are properly installed.
2. If the engine case is excessively greasy, ap-
ply degreaser with a paint brush. Do not ap-
ply degreaser to the wheel axles.
3. Rinse the dirt and degreaser off with a garden
hose. Use only enough pressure to do the
job.
EE.book Page 1 Friday, May 27, 2005 5:00 PM

9-5
7. Automotive type wax may be applied to all
painted and chrome plated surfaces. Avoid
combination cleaner-waxes. Many contain
abrasives which may mar the paint or protec-
tive finish.
When finished, start the engine and let it idle for
several minutes.
WARNING
Wet brakes may have reduced stopping ability,
increasing the chance of an accident. Test the
brakes after washing. Apply the brakes several
times at slow speeds to let friction dry out the
linings.
EE.book Page 5 Friday, May 27, 2005 5:00 PM

9-7
EBU00427
B. STORAGE
Long term storage (60 days or more) of your ma-
chine will require some preventive procedures to
guard against deterioration. After thoroughly
cleaning the machine, prepare for storage as fol-
lows:
1. Fill the fuel tank with fresh fuel and add fuel
stabilizer (if available).NOTE:Use of fuel stabilizer eliminates the need to drain
the fuel system. Consult a Yamaha dealer if the
fuel system is to be drained instead.2. Remove the spark plug, pour about one ta-
blespoon of SAE 10W30 or 20W40 motor oil
in the spark plug hole and reinstall the spark
plug. Ground the spark plug wire and turn the
engine over several times to coat the cylinder
wall with oil.
3. Lubricate all control cables.
4. Block up the frame to raise all wheels off the
ground.
EE.book Page 7 Friday, May 27, 2005 5:00 PM