2004 YAMAHA YFM50S engine

EBU00296
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 experience
to do so. However, the idling speed may be per-
formed by the owner as a part of the usual main-
tenance routine.
cC
The carburetor was set at the Yamaha facto-
ry after many tests. If the settings are dis-
turbed by someone without sufficient techni-
cal knowledge, poor engine performance and
damage may result.
8-35
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8-37
EBU01143
Idle speed adjustment
NOTE:
A diagnostic tachometer must be used for this
procedure.
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. Connect the tachometer and set the idle to
the specified idling speed by adjusting the
throttle stop screw. Turn the screw in direc-
tion ato increase the engine speed, and
in direction bto decrease the engine
speed.q
a b
1. Throttle stop screw1. Vis de butée de papillon1. Tornillo tope del acelerador
Specified idle speed:
1,700–1,900 r/min
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8-39
EBU00303
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.
EBU00304
Cam chain adjustment
The cam chain becomes loose with use, result-
ing in improper valve timing and engine noise.
To prevent this, the cam chain tensioner must
be adjusted regularly. This adjustment should be
left to a Yamaha service technician.
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8-51
EBU00570
Cable inspection and lubrication
w
Inspect cables frequently and replace if dam-
aged. Corrosion can result when the outer
covering of control cables becomes dam-
aged. Cables can also become frayed or
kinked. Operation 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
5YF-9-60 8 4/24/03 6:35 PM Page 8-51

EBU00440
Troubleshooting chart
1. Fuel
Check if there is
fuel in the fuel
tank
2. Compression
Use electric starter
to see if there is
compression
3. Ignition
Remove spark plug
and check electrodes
WetWipe clean with dry
cloth
DryAttach spark plug cap
and ground to chassisUse electric
starterSpark weak
Spark goodIgnition system normal
No spark
Ask a Yamaha dealer to inspect
Adjust spark plug gap
or replace spark plug
There is compressonCompression normal
Ask a Yamaha dealer to inspectNo compression
There is fuelTurn the fuel
cock to “OFF”
Remove the
fuel hose from
the fuel cock.
Some fuelTurn the fuel
cock to “RES”Restart engine
No fuelSupply fuel
4. Battery
Use electric
starter
Engine turns
over quicklyBattery good
Engine turns
over slowlyCheck fluid, recharge,
check connections
Check fuel flow
Water or dirt
mixed in fuel
Turn the fuel
cock to “ON”No fuelFuel cock clogged
Clean the fuel filter
and the fuel tank
Clean fuel cock
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9-1
EBU00420
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
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 degreaser to the wheel axles.
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9-5
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 pro-
tective finish.
When finished, start the engine and let it
idle for several minutes.
w
Wet brakes may have reduced stopping abili-
ty, 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.
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9-7
EBU00427
B. STORAGE
Long term storage (60 days or more) of your
machine will require some preventive proce-
dures to guard against deterioration. After thor-
oughly cleaning the machine, prepare for stor-
age as follows:
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
tablespoon of SAE 10W30 or 20W40
motor oil in the spark plug hole and rein-
stall 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.
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