2021 YAMAHA YFZ50 engine

Your ATV was delivered with an adjustable speed limiter. Yamaha recommends that all beginners start off
to limit the amount of speed available while they learn. 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 limiter will result in a significant increase in power, turn the vehicle speed
limiter adjusting screw completely back in again; adjust it out in stages as done previously.
If your child is a beginner or is inexperienced, he or she should take a training course.UBW464E0.book Page 2 Thursday, January 23, 2020 2:42 PM

EBU17421
TABLE OF CONTENTS
VEHICLE IDENTIFICATION ............................ 1-1Identification numbers ................................ 1-1
LOCATION OF THE WARNING AND
SPECIFICATION LABELS .............................. 2-1
SAFETY INFORMATION ................................ 3-1
DESCRIPTION................................................ 4-1 Left view ...................................................... 4-1
Right view.................................................... 4-1
Controls and instruments............................ 4-2
INSTRUMENT AND CONTROL
FUNCTIONS ................................................... 5-1 Main switch ................................................. 5-1
Handlebar switches .................................... 5-1
Engine stop switch with lanyard ................. 5-2
Throttle lever ............................................... 5-3
Speed limiter ............................................... 5-3
Front brake lever ......................................... 5-5
Rear brake lever .......................................... 5-6
Parking brake .............................................. 5-6
Kickstarter ................................................... 5-7 Fuel tank cap .............................................. 5-8
Fuel ............................................................. 5-9
Fuel cock .................................................. 5-10
Starter (choke) ......................................... 5-12
Seat .......................................................... 5-13
Rear shock absorber ................................ 5-13
PRE-OPERATION CHECKS .......................... 6-1 Fuel ............................................................. 6-3
Engine oil .................................................... 6-3
Transmission oil .......................................... 6-3
Front and rear brakes ................................. 6-3
Throttle lever ............................................... 6-3
Drive chain .................................................. 6-3
Tires ............................................................ 6-3
Chassis fasteners ....................................... 6-6
Instruments and switches........................... 6-6
OPERATION .................................................. 7-1 Starting a cold engine................................. 7-1
Starting a warm engine............................... 7-3
Engine break-in........................................... 7-3
Parking........................................................ 7-3
Parking on a slope ...................................... 7-4UBW464E0.book Page 1 Thursday, January 23, 2020 2:42 PM

Accessories and loading ............................. 7-5
RIDING YOUR ATV ........................................ 8-1 GETTING TO KNOW YOUR ATV ................ 8-2
RIDE WITH CARE AND GOOD JUDGMENT .............................................. 8-2
BE CAREFUL WHERE YOU RIDE ............... 8-9
TURNING YOUR ATV................................ 8-12
CLIMBING UPHILL ................................... 8-13
RIDING DOWNHILL .................................. 8-16
CROSSING A SLOPE................................ 8-17
CROSSING THROUGH SHALLOW WATER .................................................... 8-18
RIDING OVER ROUGH TERRAIN ............. 8-20
SLIDING AND SKIDDING .......................... 8-20
WHAT TO DO IF... ..................................... 8-21
PERIODIC MAINTENANCE AND
ADJUSTMENT................................................ 9-1 Owner’s Manual and tool kit ....................... 9-2
Periodic maintenance chart: Emission control system .......................................... 9-3
Periodic maintenance chart: General maintenance and lubrication..................... 9-5
Removing and installing the panel .............. 9-9
Checking the spark plug ............................. 9-9
Engine oil................................................... 9-11 Why Yamalube.......................................... 9-14
Transmission oil ........................................ 9-15
Cleaning the air filter element ................... 9-16
Cleaning the spark arrester ...................... 9-19
Adjusting the carburetor ........................... 9-20
Adjusting the engine idling speed ............ 9-20
Adjusting the throttle lever free play ......... 9-22
Valve clearance......................................... 9-22
Brakes....................................................... 9-22
Checking the front and rear brake
shoes ...................................................... 9-23
Adjusting the front brake lever free play... 9-24
Adjusting the rear brake lever free play .... 9-26
Drive chain slack....................................... 9-26
Cleaning and lubricating the drive chain ....................................................... 9-29
Checking and lubricating the cables ........ 9-29
Checking and lubricating the front and rear brake levers ..................................... 9-30
Checking the wheel hub bearings ............ 9-30
Lubricating the front arm pivots ............... 9-31
Lubricating the front knuckle pivots ......... 9-31
Lubricating the steering shaft ................... 9-32
Battery ...................................................... 9-32
Replacing the fuse .................................... 9-35
Removing a wheel .................................... 9-36
Installing a wheel ...................................... 9-36
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3-1
3
EBU17432
SAFETY INFORMATION
SAFETY INFORMATION
EBU36352AN ATV IS NOT A TOY AND CAN BE HAZARD-OUS TO OPERATE.An ATV handles differently from other vehicles, in-
cluding motorcycles and cars. A collision or roll-
over can occur quickly, even during routine
maneuvers such as turning and riding on hills or
over obstacles, if you fail to take proper precau-
tions.
SEVERE INJURY OR DEATH can result if you do
not follow these instructions:
Read this manual and all labels carefully and fol-
low the operating procedures described.
 Never operate an ATV without proper training or
instruction. Take a training course. Beginners
should receive training from a certified instruc-
tor. Contact an authorized ATV dealer to find
out about the training courses nearest you.
 Always follow the age recommendation:
– A child under 6 years old should never operate
an ATV with engine size greater than 50 cc. – A child under 12 years old should never oper-
ate an ATV with engine size greater than 70 cc.
– A child under 16 years old should never oper-
ate an ATV with engine size greater than 90 cc.
 Never allow a child under age 16 to operate an
ATV without adult supervision, and never allow
continued use of an ATV by a child if he or she
does not have the abilities to operate it safely.
 Never carry a passenger on an ATV.
 This vehicle is intended for off-road use only. Do
not operate on any paved surfaces such as:
sidewalks, driveways, parking lots, paved
roads, public streets or other motorway.
 Watch carefully for other vehicles when operat-
ing on unpaved public streets or roads. Make
sure you know your country’s laws and regula-
tions before you ride on unpaved public streets
or roads.
 Never operate an ATV without wearing an ap-
proved motorcycle helmet that fits properly.
You should also wear eye protection (goggles
or face shield), gloves, boots, a long-sleeved
shirt or a jacket, and long pants.UBW464E0.book Page 1 Thursday, January 23, 2020 2:42 PM

3-4
3
In the event of an accident
1. If serious injuries are incurred, you may be safer staying next to your vehicle; it may
shield you from oncoming riders. Depending
on your injuries and position in the trail; you
must make a judgment call as to whether you
should move to a position off the trail. If you
have sustained head, neck, or back injuries,
or cannot feel your limbs, you should not
move. Keep your helmet on and remain mo-
tionless. Lie down next to your vehicle and
wait for help.
2. If less serious injuries are incurred and you can walk, then move to a position off the trail.
Check yourself for injuries and apply first aid
as needed.
3. If your injuries are light, when safe to do so, move your vehicle off the trail to avoid colli-
sions with oncoming riders. Check for injuries
and apply first aid as necessary. If you can
physically operate your vehicle, inspect your
vehicle. If the vehicle is in safe operating con-
dition and you can safely operate it, restart it
and ride gently back to camp or other known
location where you can receive medical at- tention. If necessary, contact your riding party
or local authorities to let them know where
you are and what has happened.
In the event of a breakdown 1. If your vehicle will not restart or is not in safe operating condition, turn off the main switch
and engine stop switch. If the breakdown oc-
curs at twilight or night, leave the main switch
on so that your lights may warn other riders of
your stopped vehicle.
2. Get out of danger. Check for oncoming vehi- cles and when safe, push your vehicle to the
side of the trail or even off the main trail to
avoid any possible collisions with oncoming
riders. If you cannot move your vehicle by
yourself, when safe, walk to the nearest van-
tage point and signal an oncoming rider to
help you push your vehicle to a safe place off
the trail.
3. Inspect your vehicle for any immediate haz- ardous conditions. The most obvious hazard-
ous conditions are leaking fuel and
ungrounded or broken wiring. Visually check
for broken wiring and leaking fuel. Leaking
fuel can be confirmed by the odor of gasoline.
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3-5
34. Once immediate safety hazards are con-
firmed not to exist, you may remove your hel-
met to more closely inspect your vehicle.
Check for external signs of wear, broken
parts, fluid leaks, cracks in the frame, sus-
pension damage, wheel damage, and so on.
Fuel, oil, and coolant usually give off a notice-
able odor.
5. If your vehicle will not restart or if it is unsafe to ride, then turn off all vehicle systems (en-
gine stop switch, main switch, and fuel cock),
and then signal or go for help.
Aftermarket Parts, Accessories, and Modifica-
tions
While you may find aftermarket products similar in
design and quality to genuine Yamaha accesso-
ries, recognize that some aftermarket accessories
or modifications are not suitable because of po-
tential safety hazards to you or others. Installing
aftermarket products or having other modifica-
tions performed to your vehicle that change any of
the vehicle’s design or operation characteristics
can put you and others at greater risk of serious
injury or death. You are responsible for injuries re-
lated to changes in the vehicle. Keep the following guidelines in mind, as well as those found in the
Loading section (page 7-6) when mounting acces-
sories.

Never install accessories that would impair the
performance of your ATV. Carefully inspect the
accessory before using it to make sure that it
does not in any way reduce ground clearance,
limit suspension travel, steering travel or control
operation.
 Accessories fitted to the ATV can create insta-
bility due to improper weight distribution.
 Bulky or large accessories may seriously affect
the stability of the ATV.
 Certain accessories can displace the operator
from his or her normal riding position. This im-
proper position limits the freedom of movement
of the operator and may limit control ability,
therefore, such accessories are not recom-
mended.
 Use caution when adding electrical accesso-
ries. If electrical accessories exceed the capac-
ity of the ATV’s electrical system, an electric
failure could result, which could cause a dan-
gerous loss of lights or engine power. Also, the
battery tends to discharge more quickly if elec-
trical accessories are added.
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3-6
3
TEACHING YOUR CHILD TO OPERATE THE
ATV
WARNING
EWB00081Never let your child ride an ATV without close
adult supervision (a child under 6 should not
ride this ATV even with adult supervision).
Promptly correct your child if he or she begins
to ride beyond his or her abilities and, if neces-
sary, intervene by pulling the cord (lanyard) to
stop the engine.
If the child rides beyond his or her abilities, or
rides in terrain that is too difficult, he or she
may lose control of the ATV, causing an acci-
dent.
Introduce new riding areas slowly and make
sure the riding area matches your child’s skill
level. You must make the commitment to your child’s
proper use of the ATV. Your child must rely upon
you to be sure he or she has the development,
proper training, and proper equipment, as well as
an appropriately sized ATV and an appropriate rid-
ing area. Be sure your child is ready to learn how to ride
As a parent, your first step is to decide when your
child has the strength, skills, and judgment to
learn how to operate an ATV safely. Re-evaluate
your child’s readiness before every use; a child
who is too tired or distracted should not be al-
lowed to operate the ATV.
Be sure your child is properly trained
Your child should take a certified training course.
Training will continue with you as the instructor, so
you should be sure you thoroughly understand
proper riding techniques before continuing to in-
struct your child. Go through this Owner’s Manual
page by page with your child and be sure he or
she understands how to operate the ATV properly.
Be sure your child is wearing all the proper
safety equipment
Your child must always wear an approved motor-
cycle helmet that fits properly. Your child should
also wear the safety equipment described in the
Riding Your ATV section of this manual.UBW464E0.book Page 6 Thursday, January 23, 2020 2:42 PM

3-7
3Choose an appropriate riding area
Select an area appropriate for your child to learn
to ride. (See page 8-9.) 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 5-3.) 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.
UBW464E0.book Page 7 Thursday, January 23, 2020 2:42 PM