engine YAMAHA YFM50R 2008 Service Manual

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poor performance and possible engine over-
heating.
EBU27630
Cleaning the spark arrester
Be sure the exhaust pipe and muffler are cool be-
fore cleaning the spark arrester.
1. Remove the screws.
2. Remove the tailpipe by pulling it out of the
muffler.
3. Tap the tailpipe lightly, and then use a wire
brush to remove any carbon deposits from the
spark arrester portion of the tailpipe and insideof the tailpipe housing.
4. Insert the tailpipe into the muffler and align the
screw holes.
5. Install the screws and tighten them.WARNING
EWB02340
Do not start the engine when cleaning the
spark arrester, otherwise it could cause injury
to the eyes, burns, carbon monoxide poison-
ing, possibly leading to death, and start a fire.
Always let the exhaust system cool prior to
1. Screw
1

1. Tailpipe
2. Spark arrester
3. Screw
21
3

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touching exhaust components.
EBU23940
Adjusting the carburetor
The carburetor should be checked and, if neces-
sary, adjusted at the intervals specified in the peri-
odic maintenance and lubrication chart. The
carburetor is an important part of the engine and
requires very sophisticated adjustment. Therefore,
most carburetor adjustments should be left to a
Yamaha dealer, who has the necessary profes-
sional knowledge and experience. The adjustment
described in the following section, however, may
be performed by the owner as part of routine main-
tenance.
CAUTION:

ECB00480
The carburetor has been set and extensively
tested at the Yamaha factory. Changing these
settings without sufficient technical knowl-
edge may result in poor performance of or
damage to the engine.
EBU24000
Adjusting the engine idling speed
The engine idling speed must be checked and, ifnecessary, adjusted as follows at the intervals
specified in the periodic maintenance and lubrica-
tion chart.
NOTE:

A diagnostic tachometer is needed to make this
adjustment.
1. Start the engine and warm it up.
NOTE:

The engine is warm when it quickly responds to the
throttle.
2. Attach the tachometer to the spark plug lead.
3. Check the engine idling speed and, if neces-
sary, adjust it to specification by turning the
throttle stop screw at the carburetor. To in-
crease the engine idling speed, turn the throt-
tle stop screw in direction (a), and to decrease
it, turn the screw in direction (b).

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NOTE:

If the specified idling speed cannot be obtained as
described above, have a Yamaha dealer make the
adjustment.
EBU27071
Checking the throttle cable free play
The throttle cable free play should be checked at
the intervals specified in the periodic maintenance
and lubrication chart.The throttle cable free play should measure 1.0–
3.0 mm (0.04–0.12 in) at the throttle lever. Period-
ically check the throttle cable free play and, if nec-
essary, have a Yamaha dealer adjust it.
EBU24060
Valve clearance
The valve clearance changes with use, resulting in
improper air-fuel mixture and/or engine noise. To
prevent this from occurring, the valve clearance
must be adjusted by a Yamaha dealer at the inter-
vals specified in the periodic maintenance and lu-
brication chart.
1. Throttle stop screw
Engine idling speed:
1750–1850 r/min
1 (a) (b)

1. Throttle lever free play
1

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adjusting nut on the brake cable at the rear
wheel hub in direction (a), and to decrease it,
turn the nut in direction (b).
7. Tighten the locknut at the brake lever.
NOTE:

If the specified free play cannot be obtained as de-
scribed above or if the rear brake does not operate
correctly, have a Yamaha dealer check the internal
rear brake mechanism.
WARNING
EWB02080
Operating with improperly serviced or adjust-
ed brakes could cause loss of braking ability,
which could lead to an accident.
After servicing:

Make sure the brakes operate smoothly and
that the free play is correct.

Make sure the brakes do not drag.
Replacement of brake components requires
professional knowledge. These procedures
should be performed by a Yamaha dealer.
EBU24900
Checking and lubricating the cables
The operation and the condition of all control ca-
bles should be checked before each ride, and the
cables and cable ends should be lubricated if nec-
essary. If a cable is damaged or does not move
smoothly, have a Yamaha dealer check or replace
it.
1. Brake lever free play adjusting nut
1
(a)(b)

Recommended lubricant:
Engine oil

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EBU25791
Troubleshooting chart
Check the fuel level in
the fuel tank.1. Fuel
There is enough fuel.
There is no fuel.
Check the compression.
Supply fuel.
The engine does not start.
Check the compression.
Operate the electric starter.2. Compression
There is compression.
There is no compression.
Check the ignition.
Have a Yamaha dealer
check the ATV.
Remove the spark plug
and check the electrodes.3. Ignition
Wipe off with a dry cloth and correct the
spark plug gap, or replace the spark plug.
Have a Yamaha dealer check the ATV.
The engine does not start.
Have a Yamaha dealer
check the ATV.
The engine does not start.
Check the battery.
Operate the electric starter.4. Battery
The engine turns over
quickly.
The engine turns over
slowly.
The battery is good.Check the electrolyte level, recharge the
battery and check the lead connections.
DryWet
Open the throttle halfway and operate
the electric starter.

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EBU25860
CLEANING AND STORAGE
EBU25880
Cleaning
Frequent, thorough cleaning of your ATV will not
only enhance its appearance but will improve its
general performance and extend the useful life of
many components.
1. Before cleaning the ATV:
a. Block off the end of the exhaust pipe to
prevent 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, apply
degreaser with a paint brush. Do not apply de-
greaser to the wheel axles.
3. Rinse the dirt and degreaser off with a garden
hose. Use only enough pressure to do the job.
CAUTION:

ECB00710
Excessive water pressure may cause water
seepage and deterioration of wheel bearings,
brakes, transmission seals and electrical de-
vices. Many expensive repair bills have result-
ed from improper high-pressure detergentapplications such as those available in coin-
operated car washers.
4. Once most of the dirt has been hosed off,
wash all surfaces with warm water and mild,
detergent-type soap. An old toothbrush or bot-
tle brush is handy for hard-to-reach places.
5. Rinse the ATV off immediately with clean wa-
ter and dry all surfaces with a chamois, clean
towel or soft absorbing cloth.
6. Clean the seat with a vinyl upholstery cleaner
to keep the cover pliable and glossy.
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 cleaning, start the
engine and let it idle for several minutes.WARNING
EWB02310
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

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linings.
EBU25932
Storage
Short-term
Always store your ATV in a cool, dry place and, if
necessary, protect it against dust with a porous
cover.
CAUTION:

ECB00720

Storing the ATV in a poorly ventilated room
or covering it with a tarp while it is still wet,
will allow water and humidity to seep in and
cause rust.

To prevent corrosion, avoid damp cellars,
stables (because of the presence of ammo-
nia) and areas where strong chemicals are
stored.
Long-term
Before storing your ATV for several months:
1. Follow all the instructions in the “Cleaning”
section of this chapter.
2. Turn the fuel cock lever to “OFF”.
3. Drain the carburetor float chamber by loosen-ing the drain bolt; this will prevent fuel deposits
from building up. Pour the drained fuel into the
fuel tank.
4. Fill up the fuel tank and add fuel stabilizer (if
available) to prevent the fuel from deteriorat-
ing.
5. Perform the following steps to protect the cyl-
inder, piston rings, etc. from corrosion.
a. Remove the spark plug cap and spark
plug.
b. Pour a teaspoonful of engine oil into the
spark plug bore.
c. Install the spark plug cap onto the spark
plug, and then place the spark plug on the
cylinder head so that the electrodes are
grounded. (This will limit sparking during
the next step.)
d. Turn the engine over several times with
the starter. (This will coat the cylinder wall
with oil.)
e. Remove the spark plug cap from the spark
plug, and then install the spark plug and Specified amount:
7.5 ml of stabilizer to each liter of fuel (or 1 oz
of stabilizer to each gallon of fuel)

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EBU25960
SPECIFICATIONS
EBU2597A
Dimensions:
Overall length:
1537 mm (60.5 in)
Overall width:
825 mm (32.5 in)
Overall height:
915 mm (36.0 in)
Seat height:
618 mm (24.3 in)
Wheelbase:
1030 mm (40.6 in)
Ground clearance:
75 mm (3.0 in)
Minimum turning radius:
2300 mm (91 in)
Weight:
With oil and fuel:
115.0 kg (254 lb)
Engine:
Engine type:
Air cooled 4-stroke, SOHC
Cylinder arrangement:
Forward-inclined single cylinder
Displacement:
49.0 cm
3

Bore
×
stroke:
39.0
×
41.4 mm (1.54
×
1.63 in)
Compression ratio:
10.30 :1
Starting system:
Electric starter
Lubrication system:
Wet sump

Engine oil:
Type:
SAE5W30 or SAE10W30 or SAE10W40 or SAE15W40
or SAE20W40 or SAE20W50
Recommended engine oil grade:
API service SG type or higher, JASO standard MA
-20˚-10˚0˚
10˚20˚30˚40˚50˚C
10W/30
15W/4020W/4020W/50
10W/40
5W/30

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Engine oil quantity:
Periodic oil change:
0.80 L (0.85 US qt) (0.70 Imp.qt)
Final gear oil:
Type:
SAE80 API GL-4 Hypoid gear oil
Quantity:
0.12 L (0.13 US qt) (0.11 Imp.qt)
Air filter:
Air filter element:
Wet element
Fuel:
Recommended fuel:
Regular unleaded gasoline only (EUR)
Unleaded gasoline only (AUS)(NZL)
Fuel tank capacity:
6.8 L (1.80 US gal) (1.50 Imp.gal)
Fuel reserve amount:
0.9 L (0.24 US gal) (0.20 Imp.gal)
Carburetor:
Manufacturer:
MIKUNI
Type x quantity:
VM16SH x 1
Spark plug (s):
Manufacturer/model:
NGK/CR7HSA
Spark plug gap:
0.6–0.7 mm (0.024–0.028 in)
Clutch:
Clutch type:
Wet, multiple-disc automatic
Transmission:
Primary reduction system:
Spur gear
Primary reduction ratio:
65/20 (3.250)
Secondary reduction system:
Shaft drive
Secondary reduction ratio:
19/18
×
34/10 (3.588)
Transmission type:
Constant mesh 1-speed
Operation:
Left hand operation
1st:
38/14 (2.714)
Chassis:
Frame type:
Steel tube frame
Caster angle:
1.0 °
Trail:
3.4 mm (0.13 in)
Front tire:
Type:
Tubeless
Size:
AT16 x 7-7

INDEX
A
Accessories and loading ................................................ 6-7
Air filter element, cleaning ............................................ 8-13
B
Battery .................................................................. 5-6
,
8-26
Brake lever free play, adjusting the front...................... 8-21
Brake lever free play (rear), adjusting .......................... 8-23
Brake lever, front ............................................................ 4-6
Brake lever, rear............................................................. 4-6
Brake levers, checking and lubricating......................... 8-25
Brakes, front and rear .................................................... 5-3
Brake shoes, checking the front and rear .................... 8-20
C
Cables, checking and lubricating ................................. 8-24
Carburetor, adjusting.................................................... 8-18
Chassis fasteners........................................................... 5-6
Choke ........................................................................... 4-10
Cleaning ......................................................................... 9-1
D
Drive select lever............................................................ 4-7
E
Engine break-in .............................................................. 6-5
Engine, cold start ........................................................... 6-1
Engine idling speed ...................................................... 8-18
Engine oil ............................................................... 5-3
,
8-9
Engine, starting a warm ................................................. 6-3Engine stop switch ......................................................... 4-2
Engine stop switch with lanyard ..................................... 4-2
F
Final gear oil......................................................... 5-3
,
8-12
Front knuckle pivots, lubricating ................................... 8-25
Fuel ........................................................................ 4-8
,
5-3
Fuel cock ........................................................................ 4-9
Fuel tank cap.................................................................. 4-7
Fuse, replacing............................................................. 8-28
H
Handlebar switches ........................................................ 4-2
I
Identification numbers .................................................. 11-1
Indicator light .................................................................. 4-1
Instruments, lights and switches .................................... 5-6
K
Key identification number ............................................. 11-1
L
Label locations ............................................................... 2-1
M
Main switch .................................................................... 4-1
Maintenance and lubrication chart ................................. 8-5
Maintenance chart, emission control system ................. 8-3
Model label ................................................................... 11-2
N
Neutral indicator light ..................................................... 4-1