2017 YAMAHA YFZ50 engine

2-7
2
Choose an appropriate riding area
Select an area appropriate for your child to learn
to ride. (See page 7-9.) Follow the instructions in
the Riding Your ATV section of this manual.
Choose a large, flat, unpaved road or area that is
free of obstacles and away from other vehicles.
Supervise every use of the ATV
Because an adult must supervise every ATV oper-
ator under age 16, you should closely watch your
child every time he or she uses the ATV. Be ready
to intervene immediately if the child is not operat-
ing according to your guidelines. This ATV is fitted
with an engine stop switch cord (lanyard) device
that will let you stop the engine remotely as you
walk behind the vehicle.
ENGINE STOP SWITCH CORD
This model has an engine stop switch cord (lan-
yard) designed for use by an adult supervising the
child operating the ATV. When using the engine
stop switch cord, be sure the speed limiter on the
handlebar is adjusted and the engine speed limiter
plate is installed to limit the ATV to a walking
speed. (See page 4-3.) 1. Install the cap on the end of the engine stop
switch cord onto the engine shut-off switch
(white button).
2. Put your fingers in the loop at the other end of the cord.
3. As your child is riding, walk behind the ATV, closely watching his or her actions as well as
the path ahead.
4. If there is a potential hazard ahead or if your child is not riding correctly, pull firmly on the
cord (lanyard) to stop the engine. Because
the ATV will continue to roll for some dis-
tance, allow extra time and distance to pull
the cord before a potentially hazardous situa-
tion might be encountered.
When your child has developed sufficient skill to
no longer need you to follow with the cord, se-
curely tie up the cord. However, you must still
closely supervise your child at all times during ATV
operation.
TIPThe ATV will not start without the cap in place. Be
sure to remove the cord and store it in a safe place
to prevent operation of the ATV when you are not
around to supervise.
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2-8
2
WARNING
EWB00073Avoid Carbon Monoxide Poisoning
All engine exhaust contains carbon monoxide,
a deadly gas. Breathing carbon monoxide can
cause headaches, dizziness, drowsiness, nau-
sea, confusion, and eventually death.
Carbon Monoxide is a colorless, odorless,
tasteless gas which may be present even if you
do not see or smell any engine exhaust. Deadly
levels of carbon monoxide can collect rapidly
and you can quickly be overcome and unable
to save yourself. Also, deadly levels of carbon
monoxide can linger for hours or days in en-
closed or poorly ventilated areas. If you experi-
ence any symptoms of carbon monoxide
poisoning, leave the area immediately, get
fresh air, and SEEK MEDICAL TREATMENT.
Do not run engine indoors. Even if you try to
ventilate engine exhaust with fans or open
windows and doors, carbon monoxide can
rapidly reach dangerous levels.
 Do not run engine in poorly ventilated or par-
tially enclosed areas such as barns, garages,
or carports. 
Do not run engine outdoors where engine
exhaust can be drawn into a building through
openings such as windows and doors.

WARNING
EWB02592When transporting the ATV in another vehicle,
be sure it is kept upright and that the fuel cock
is in the “OFF” position. Otherwise, fuel may
leak out of the carburetor or fuel tank.
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3-1
3
EBU17681
DESCRIPTION
EBU17691Left view
EBU17701Right view
1. Fuel tank cap
2. Fuel cock
3. Air filter
4. Engine stop switch with cord (lanyard)
5. Rear shock absorber assembly spring preload adjusting ring
6. Kickstarter lever cap
7. Throttle stop screw
12
4
5
3
6
7
1. Spark arrester
2. Owner’s tool kit
3. Fuse
4. Battery
5. Spark plug
6. Engine oil filler cap
7. Transmission oil filler cap
12
3,4
5
67
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4-1
4
EBU17738
INSTRUMENT AND CONTROL FUNCTIONS
EBU33850Main switchThe positions of the main switch are as follows:
ON
All electrical systems are supplied with power, and
the engine can be started. The key cannot be re-
moved.
OFF
All electrical systems are off. The key can be re-
moved.
EBU18066Handlebar switchesEBU18081Engine stop switch “ / ”
Set this switch to “ ” before starting the engine.
The engine stop switch controls the ignition and
stops the engine when it is running. Use this
switch to stop the engine in an emergency situa-
tion. The engine will not start or run when this
switch is set to “ ”.
ON
OFF
1. Engine stop switch “ / ”
2. Start switch “ ”
21
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4-2
4
EBU18102Start switch “ ”
Push this switch to crank the engine with the start-
er. See the starting instructions on page 6-1 prior
to starting the engine.EBU36341Engine stop switch with lanyardThe cap must be attached to the engine stop
switch for the engine to run.
The lanyard should be held by putting your fingers
in the loop as shown.Should the ATV be separated from the parent by a
distance longer than the lanyard length, the lan-
yard will pull out the cap and stop the engine.
For further explanation of this switch and the lan-
yard, see “TEACHING YOUR CHILD TO OPER-
ATE THE ATV” in the “SAFETY INFORMATION”
section.
TIP
The engine cannot be started with the cap re-
moved.
1. Engine stop switch
2. Cap
3. Lanyard12
3
1. Lanyard
1
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4-3
4

When your child has developed sufficient skill to
no longer need you to follow with the lanyard,
securely tie up the lanyard. However, you must
still closely supervise your child at all times dur-
ing ATV operation.
EBU18283Throttle leverOnce the engine is running, pushing the throttle le-
ver will increase the engine speed.
Regulate the speed of the ATV by varying the
throttle position. Because the throttle is spring-
loaded, the ATV will decelerate, and the engine
will return to an idle any time the throttle lever is re-
leased. Before starting the engine, check the throttle to be
sure it is operating smoothly. Make sure it returns
to the idle position as soon as the lever is released.
EBU36330Speed limiterYour ATV was delivered with two speed limiter de-
vices. A vehicle speed limiter adjusting screw and
a removable engine speed limiter plate. Yamaha
recommends that all beginning riders start off with
the vehicle speed limiter adjusting screw fully
turned in and the engine speed limiter plate in-
stalled to limit the amount of speed available while
they learn.1. Throttle lever
1
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4-4
4The vehicle speed limiter keeps the throttle from
fully opening, even when the throttle lever is
pushed to the maximum. The adjusting screw may
be gradually turned out as the beginner becomes
more familiar with operating the ATV. Parents
should decide when to adjust the ATV for more
power as their youngster’s riding skills improve.
Once the ATV rider can operate with skill at the top
speed permitted by adjusting the vehicle speed
limiter alone, the engine speed limiter plate can be
removed. Since removal of this plate will result in
a significant increase in power, turn the vehicle
speed limiter adjusting screw completely back in
again and adjust it out in stages as done previous-
ly.
Vehicle speed limiter
1. Loosen the locknut.
2. To increase the maximum engine power available and the maximum speed of the ATV,
turn the adjusting screw in direction (a). To
decrease the maximum engine power avail-
able and the maximum speed of the ATV, turn
the adjusting screw in direction (b). Do not
turn the adjusting screw out more than 11
mm (0.43 in) or the throttle cable could be
damaged. Always make sure the throttle lever free play is adjusted to 2.0–3.2 mm (0.08–
0.13 in). (See page 8-21.) WARNING! Im-
proper adjustment of the speed limiter and
throttle could cause throttle cable damage
or improper throttle operation. You could
lose control, resulting in an accident.
[EWB00242]
3. Tighten the locknut.1. Locknut
2. Adjusting screw
3. No more than 11 mm (0.43 in)
1
3
2
(b)
(a)
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4-5
4
Engine speed limiter plate
When the engine speed limiter plate is installed,
engine speed is limited to 5200 r/min. When this
plate is removed, top engine speed (7400 r/min) is
available.
Remove the plate as follows.
1. Remove panel A. (See page 8-9.)
2. Loosen the screws, and then remove the plate as shown.
3. Tighten the screws.
4. Install the panel.
TIPStore the engine speed limiter plate with the own-
er’s manual so that it is readily available whenever
you want to reduce top engine speed. EBU18392Front brake leverThe front brake lever is located on the right han-
dlebar. To apply the front brake, pull the brake le-
ver toward the handlebar grip.
1. Screw
2. Engine speed limiter plate
21
1. Front brake lever
1
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