2003 YAMAHA BIG BEAR PRO 400 engine

8-37 1. Spark plug cap
1. Capuchon de bougie
1. Tapa de bujía
1. Spark plug wrench
1. Clé à bougie
1. Llave de bujías
EBU00680
Spark plug inspection
Removal
1. Remove the spark plug cap.
2. Use the spark plug wrench in the tool kit to re-
move the spark plug as shown.
Inspection
The spark plug is an important engine component
and is easy to inspect. The condition of the spark
plug can indicate the condition of the engine.
The ideal color on the white insulator around the
center electrode is a medium-to-light tan color for a
ATV that is being ridden normally.
Do not attempt to diagnose such problems your-
self. Instead, take the ATV to a Yamaha dealer.
You should periodically remove and inspect the
spark plug because heat and deposits will cause
the spark plug to slowly break down and erode. If
electrode erosion becomes excessive, or if carbon
and other deposits are excessive, you should re-
place the spark plug with the specified plug.
Specified spark plug:
DR8EA (NGK)
EE.book Page 37 Monday, June 18, 2001 10:18 AM

8-45 1. Air filter element
1.Élément du filtre à air
1. Elemento filtrante
1. Element plate 2. Air filter element
3. Guide
1. Plaque d’élément 2.Élément du filtre à air
3. Guide
1. Placa del elemento 2. Elemento filtrante
3. Guía
3. Remove the air filter element, and separate it
from the guide.
4. Wash the element gently but thoroughly in
solvent.
WARNING
Always use parts cleaning solvent to clean the
air filter element. Never use low flash point sol-
vents or gasoline to clean the air filter element
because the engine could catch fire or ex-
plode.5. Squeeze the excess solvent out of the filter
and let it dry.CAUTION:
Do not twist the filter element when squeezing
it.6. Inspect the element. If damaged, replace it.
7. Apply SAE10W30 motor oil to the element.NOTE:The element should be wet but not dripping.
EE.book Page 45 Monday, June 18, 2001 10:18 AM

8-47
8. Reinstall the element to the element guide.
9. Reinstall the element assembly and parts re-
moved for access.NOTE:The air filter element should be cleaned every 20 ~
40 hours. It should be cleaned and lubricated more
often if the machine is operated in extremely dusty
areas. Each time filter element maintenance is
performed, check the air inlet to the filter case for
obstructions. Check the air cleaner rubber joint to
the carburetor and manifold fittings for an air-tight
seal. Tighten all fittings securely to avoid the pos-
sibility of unfiltered air entering the engine.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 filter element will affect carburetor jet-
ting with subsequent poor performance and
possible engine overheating.
EE.book Page 47 Monday, June 18, 2001 10:18 AM

8-49
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 Monday, June 18, 2001 10:18 AM

8-51 1. Throttle stop screw
1. Vis d’arrêt de l’accélérateur
1. Tornillo de tope del acelerador
EBU00301
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 and set the idle to
the specified idling speed by adjusting the
throttle stop screw. Turn the screw in to in-
crease engine speed, and out to decrease
engine speed.
Specified idle speed:
1,350 ~ 1,450 r/min
EE.book Page 51 Monday, June 18, 2001 10:18 AM

8-53 1. Locknut 2. Adjuster
1. Contre-écrou 2. Dispositif de réglage
1. Contratuerca 2. Ajustador
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.
EBU00305
Select lever safety system cable adjustment
The select lever safety system cable stretches
with use, resulting in improper function.
To prevent this, the cable must be adjusted regu-
larly. This adjustment, however, should be left to a
Yamaha dealer.
EE.book Page 53 Monday, June 18, 2001 10:18 AM

8-55 1. Adjusting bolt 2. Locknut a. 3 ~ 5 mm
1. Bouchon de réglage 2. Contre-écrou
1. Perno de ajuste 2. Contratuerca
1. Brake pad a. Wear limit: 1 mm
1. Plaquette de frein a. Limite d’usure: 1 mm
1. Pastillas del freno a. Límite de desgaste: 1 mm
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 ~ 5 mm.
3. Tighten the locknut.
EBU00312
Front brake pad inspection
Inspect the brake pads for damage and wear. If
the thickness is less than the specified value, have
a Yamaha dealer replace the pads.NOTE:The wheels need to be removed to inspect the
brake pads. See page 8-81 for removal proce-
dures.
EE.book Page 55 Monday, June 18, 2001 10:18 AM

8-79
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.
EBU00652
Brake and shift pedal/brake lever lubrication
Lubricate the pivoting parts of each lever and ped-
al.Recommended lubricant:
Engine oil
Recommended lubricant:
Engine oil
EE.book Page 79 Monday, June 18, 2001 10:18 AM