2001 YAMAHA YFM400F engine

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Spark plug inspection
Removal
1. Remove the spark plug cap.
2. Use the spark plug wrench in the tool kit
to remove the spark plug as shown.
Inspection
The spark plug is an important engine compo-
nent 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.
1. Spark plug wrench
1. Clé à bougie
1. Llave de bujía1. Spark plug cap
1. Capuchon de bougie
1. Tapa de bujía

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3. Remove the air filter element, and sepa-
rate 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
solvents or gasoline to clean the air filter ele-
ment because the engine could catch fire orexplode.
5. Squeeze the excess solvent out of the fil-
ter and let it dry.CAUTION:Do not twist the filter element when squeez-ing it.
6. Inspect the element. If damaged, replace
it.
7. Apply SAE 10W30 motor oil to the ele-
ment.NOTE:The element should be wet but not dripping.
1. Air filter element
1. Élément de filtre à air
1. Elemento del filtro de aire1. Air filter guide
1. Guide de filtre à air
1. Filtro de aire guía

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8. Reinstall the element to the element
guide.
9. Reinstall the element assembly and parts
removed for access.NOTE:The air filter element should be cleaned every
20 ~ 40 hours. It should be cleaned and lubri-
cated 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 man-
ifold fittings for an air-tight seal. Tighten all fit-
tings securely to avoid the possibility ofunfiltered air entering the engine.CAUTION:Never operate the engine with the air filter el-
ement removed. This will allow unfiltered air
to enter, causing rapid engine wear and possi-
ble engine damage. Additionally, operation
without the filter element will affect carbure-
tor jetting with subsequent poor performanceand possible engine overheating.
1. Connect the hose.
1. Brancher le flexible.
1. Conecte la manguera.

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Carburetor adjustment
The carburetor is a vital part of the engine and
requires very sophisticated adjustment. Most
adjusting should be left to a Yamaha dealer
who has the professional knowledge and expe-
rience to do so. However, the idling speed may
be performed by the owner as a part of the
usual maintenance routine.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 anddamage may result.

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Idle speed adjustmentNOTE:A diagnostic tachometer must be used for thisprocedure.
1. Start the engine and warm it up for a few
minutes 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. Remove panel D. (See pages 8-17 ~ 8-21
for removal and installation procedures.)
3. Connect the tachometer and set the idle to
the specified idling speed by adjusting the
throttle stop screw. Turn the screw in to
increase engine speed, and out to de-
crease engine speed.
4. Install the panel.Specified idle speed:
1,450 ~ 1,550 r/min
1. Throttle stop screw
1. Vis d’arrêt de l’accélérateur
1. Tornillo de tope del acelerador

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Valve clearance adjustment
The correct valve clearance changes with use,
resulting in improper fuel/air supply or engine
noise. To prevent this, the valve clearance
must be adjusted regularly. This adjustment
however, should be left to a professional
Yamaha service technician.

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Throttle lever adjustmentNOTE:Adjust the engine idling speed before adjust-ing the throttle lever free play.
1. Loosen the locknut.
2. Turn the adjusting bolt until the throttle le-
ver free play is 3 ~ 5 mm.
3. Tighten the locknut.
1. Locknut 2. Adjusting bolt
1. Contre-écrou 2. Bouchon de réglage
1. Contratuerca 2. Perno de ajustea. Free play
a. Jeu
a. Juego libre

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Cable inspection and lubrication
WARNING
Inspect cables frequently and replace if dam-
aged. Corrosion can result when the outer
covering of control cables becomes damaged.
Cables can also become frayed or kinked. Op-
eration of controls could be restricted, whichcould 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