engine YAMAHA YFM350R 2003 Service Manual

8-21
11. Add the specified amount of the recommend-
ed engine oil, and then install the engine oil
filler cap. Tightening torques:
Drain bolt:
32 Nm (3.2 m·kgf)
Filter cover bolt:
10 Nm (1.0 m·kgf)
Recommended oil:
See page 10-2.
Oil quantity:
Periodic oil change:
2.4 L
With oil filter replacement:
2.5 L
Total amount:
3.2 L
U5NF62.book Page 21 Wednesday, May 8, 2002 1:40 PM

8-23
CAUTION:_

In order to prevent clutch slippage (since
the engine oil also lubricates the clutch),
do not mix any chemical additives. Do not
use oils with a diesel specification of
“CD” or oils of a higher quality than spec-
ified. In addition, do not use oils labeled
“ENERGY CONSERVING II” or higher.


Make sure that no foreign material enters
the crankcase.
_12. Start the engine, and then let it idle for seve-
ral minutes while checking it for oil leakage. If
oil is leaking, immediately turn the engine off
and check for the cause.
13. Turn the engine off, and then check the oil
level and correct it if necessary.
U5NF62.book Page 23 Wednesday, May 8, 2002 1:40 PM

8-25
EBU01182
Spark plug 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.
For example, a very white center electrode porce-
lain color could indicate an intake air leak or carbu-
retion problem for that cylinder. Do not attempt to
diagnose such problems yourself.
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 elec-
trode erosion becomes excessive, you should re-
place the spark plug with one of the proper type.
Standard spark plug:
DR8EA (NGK)
U5NF62.book Page 25 Wednesday, May 8, 2002 1:40 PM

8-29 1. Check hose
1. Flexible de contrôle
1. Manguito de comprobación
1. Air filter case cover
2. Screw (× 5)
1. Couvercle du boîtier de filtre à air
2. Vis (× 5)
1. Tapa de la caja del filtro de aire
2. Tornillo (× 5)
EBU01184
Air filter cleaningNOTE:_ There is a check hose at the bottom of the air filter
case. If dust or water collects in this hose, empty
the hose and clean the air filter element and air fil-
ter case. _1. Remove the seat. (See page 4-27 for seat re-
moval and installation procedures.)
2. Remove the air filter case cover by removing
the screws.
3. Remove the air filter element.
4. Remove the air filter element from the frame.
5. Wash the air filter element gently but thor-
oughly 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. _
U5NF62.book Page 29 Wednesday, May 8, 2002 1:40 PM

8-31 1. Unlock
1. Déverrouiller
1. Levántelo
1. Element retaining plate 2. Frame
3. Air filter element
1. Plaquette de retenue d’élément 2. Guide
3.Élément du filtre à air
1. Placa de retención del elemento 2. Bastidor
3. Elemento del filtro de aire
6. Squeeze the excess solvent out of the air fil-
ter element and let it dry.CAUTION:_ Do not twist the air filter element when squeez-
ing it. _7. Inspect the air filter element. If damaged, re-
place it.
8. Apply SAE 10W30 engine oil to the air filter
element.NOTE:_ The air filter element should be wet but not drip-
ping. _9. Apply all-purpose grease to the air filter ele-
ment seat.
10. Install the air filter element on the frame.
11. Install the air filter element.
12. Install the air filter case cover by installing the
screws.
13. Install the seat.
U5NF62.book Page 31 Wednesday, May 8, 2002 1:40 PM

8-33
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 air filter element maintenance is
performed, check the air inlet to the air filter case
for obstructions. Check the air filter element rubber
joint to the carburetor and manifold fittings for an
airtight seal. Tighten all fittings securely to avoid
the possibility 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 air filter element will affect carburetor
jetting with subsequent poor performance and
possible engine overheating. _
U5NF62.book Page 33 Wednesday, May 8, 2002 1:40 PM

8-35
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.
U5NF62.book Page 35 Wednesday, May 8, 2002 1:40 PM

8-37 1. Throttle stop screw
1. Vis de butée de papillon
1. Tornillo de tope del acelerador
EBU01143
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:
1,450–1,550 r/min
U5NF62.book Page 37 Wednesday, May 8, 2002 1:40 PM

8-39 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
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.
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.
U5NF62.book Page 39 Wednesday, May 8, 2002 1:40 PM

8-65 1. O-rings
1. Joints toriques
1. Juntas tóricas
EBU00805
Lubricating the drive chain
The drive chain must be cleaned and lubricated at
the intervals specified in the periodic maintenance
and lubrication chart, otherwise it will quickly wear
out, especially when riding in dusty or wet areas.
Service the drive chain as follows.CAUTION:_ The drive chain must be lubricated after wash-
ing the ATV or riding in the rain. _1. Clean the drive chain with kerosene and a
small soft brush.CAUTION:_ To prevent damaging the O-rings, do not clean
the drive chain with steam cleaners, high-pres-
sure washers or inappropriate solvents. _2. Wipe the drive chain dry.
3. Thoroughly lubricate the drive chain with a
special O-ring chain lubricant.CAUTION:_ Do not use engine oil or any other lubricants
for the drive chain, as they may contain sub-
stances that could damage the O-rings. _
U5NF62.book Page 65 Wednesday, May 8, 2002 1:40 PM