engine YAMAHA YFZ450R 2021 User Guide

5-4
5starter will not have enough power to crank the
engine. If this should happen, remove the bat-
tery and recharge it. (See page 9-43.)
EBU18286Throttle leverPush the throttle lever to increase engine speed.
Spring tension returns the lever to the rest position
when released. Always check that the throttle le-
ver returns normally before starting the engine.
EBU18325Speed limiterThe speed limiter keeps the throttle from fully
opening, even when the throttle lever is pushed to
the maximum.
Adjusting the speed limiter1. 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
1. Throttle lever
1
1. Locknut
2. Adjusting screw
3. No more than 12 mm (0.47 in)
3
12
(a)
(b)
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5-6
5The brake lever is located on the right side of the
handlebar. To apply the front brake, pull the brake
lever toward the handlebar grip.
The brake lever is equipped with a position adjust-
ing bolt. To adjust the distance between the brake
lever and the handlebar grip, hold the brake lever
away from the handlebar so it does not contact
the adjusting bolt, loosen the locknut, turn the ad-
justing bolt, and then tighten the locknut.
EBU18434Brake pedal
The brake pedal is located on the right side of the
ATV. To apply the rear brake, push down on the
brake pedal.EBU18521Parking brake leverUse the parking brake before starting the engine
or parking the ATV, especially on a slope. To apply
the parking brake, move the parking brake lever in
direction (a). To release the parking brake, move
the parking brake lever in direction (b).
1. Brake pedal
1
1. Parking brake lever (locked position)
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5-7
5
WARNING
EWB00221Always set the parking brake before starting
the engine. The ATV could start moving un-
expectedly if the parking brake is not ap-
plied. This could cause loss of control or a
collision.
 Always be sure you have released the park-
ing brake before you begin to ride. The brake
could overheat if you ride the ATV without re-
leasing the parking brake. You could lose braking performance which could cause an
accident. You could also wear out the brakes
prematurely.
EBU18532Shift pedalThe shift pedal is located on the left side of the en-
gine and is used in combination with the clutch
when shifting. (See page 7-2.)
1. Parking brake lever (unlocked position)
1. Shift pedal
1
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5-8
5
EBU37980Fuel tank capRemove the fuel tank cap by turning it counter-
clockwise.
WARNING
EWB02522Gasoline and gasoline vapors are extremely
flammable. To avoid fires and explosions and
to reduce the risk of injury when refueling, fol-
low these instructions. 1. Before refueling, turn off the engine and besure that no one is sitting on the vehicle. Nev-
er refuel while smoking, or while in the vicinity of sparks, open flames, or other sources of
ignition such as the pilot lights of water heat-
ers and clothes dryers.
2. Do not overfill the fuel tank. When refueling, be sure to insert the pump nozzle into the fuel
tank filler hole. Stop filling when the fuel
reaches the bottom of the filler tube. Because
fuel expands when it heats up, heat from the
engine or the sun can cause fuel to spill out of
the fuel tank.1. Fuel tank cap
1
1. Maximum fuel level
2. Fuel tank filler tube
2
1
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5-10
5About the recommended fuel
Use RON 97 octane or higher. If knocking or ping-
ing occurs, try a different brand or higher octane
gasoline. Gasoline containing ethanol can be used
if the ethanol content does not exceed 10% (E10).
Gasoline containing methanol is not recommend-
ed because it can cause damage to the fuel sys-
tem or vehicle performance problems.
NOTICEECB00071Use only unleaded gasoline. The use of leaded
gasoline will cause severe damage to internal
engine parts, such as the valves and piston
rings, as well as to the exhaust system.
EBU26734SeatTo remove the seat
Insert your hand between the rear of the seat and
the rear fender, pull the seat lock lever and pull up
the seat at the rear.1. Seat lock lever
1
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6-1
6
EBU19203
PRE-OPERATION CHECKS
EBU19227Inspect your vehicle each time you use it to make sure the vehicle is in safe operating condition. Always
follow the inspection and maintenance procedures and schedules described in the Owner’s Manual.
WARNING
EWB00482Failure to inspect or maintain the vehicle properly increases the possibility of an accident or equip-
ment damage. Do not operate the vehicle if you find any problem. If a problem cannot be corrected
by the procedures provided in this manual, have the vehicle inspected by a Yamaha dealer. Before using this vehicle, check the following points:
ITEMROUTINE PAGE
Fuel • Check fuel level in fuel tank,
and add recommended fuel if neces-
sary.
• Check fuel line for leakage. Correct if necessary. 5-9, 6-4
Engine oil • Check oil level in engine oil
tank, and add recommended oil to
specified level if necessary.
• Check ATV for oil leakage. Correct if necessary. 6-4, 9-14
Coolant • Check coolant level in reservoir, and add recommended coolant to
specified level if necessary.
• Check cooling system for leakage. Correct if necessary. 6-4, 9-20
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6-4
6
EBU38000FuelMake sure there is sufficient gasoline in the tank
before starting off. Refuel if necessary. (See page
5-9.)EBU19561Engine oilMake sure that the engine oil is at the specified
level. Add oil as necessary. (See page 9-14.)EBU19632CoolantMake sure that the coolant is at the specified level.
Add coolant as necessary. (See page 9-20.)TIPThe coolant level must be checked on a cold en-
gine since the level varies with engine tempera-
ture. EBU19713Front and rear brakesBrake lever and brake pedal
Check that there is no free play in the brake le-
ver. If there is free play, have a Yamaha dealer
check the brake system. 
Check for correct brake pedal height. (See page
9-32.) If the pedal height is incorrect, have a
Yamaha dealer adjust it.
 Check the operation of the lever and pedal.
They should move smoothly and there should
be a firm feeling when the brakes are applied. If
not, have a Yamaha dealer check the brake sys-
tem.
Brake fluid level
Check the brake fluid level. Add fluid if necessary.
(See page 9-30.)
Brake fluid leakage
Check to see if any brake fluid is leaking out of the
pipe joints or brake fluid reservoirs. Apply the
brakes firmly for one minute. If there is any leak-
age, have a Yamaha dealer check the brake sys-
tem. Specified brake fluid:
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7-1
7
EBU19882
OPERATION
EBU19902Read the Owner’s Manual carefully before riding
the ATV. If there is a control or function you do not
understand, ask your Yamaha dealer.
WARNING
EWB00632Read the Owner’s Manual carefully to become
familiar with all controls in order to help pre-
vent any loss of control, which could cause an
accident or injury. EBU29954Starting the engineNOTICEECB00151See the “Engine break-in” section on page 7-4
prior to operating the engine for the first time. 1. Set the parking brake.
2. Turn the key to “ ” (on) and the engine stopswitch to “ ”.
The following warning lights should come on
for a few seconds, then go off. 
Coolant temperature warning light
 Fuel level warning light
 Engine trouble warning light
NOTICEECB00826To avoid possible damage, do not operate the
ATV if a warning light does not work as de-
scribed above. 3. Shift the transmission into neutral. The neutral
indicator light should come on, if it does not
come on, have a Yamaha dealer check the
electrical circuit.TIPThis model is equipped with an ignition circuit cut-
off system. The engine can be started under the
following conditions.
The transmission is in neutral.
 The clutch is disengaged with the transmission
in gear. However, it is recommended to shift
into neutral before starting the engine. 4. Completely close the throttle lever and start
the engine by pushing the start switch.
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7-2
7
TIPIf the engine fails to start, release the start switch,
then push it again. Pause a few seconds before
the next attempt. Each cranking should be as
short as possible to preserve battery energy. Do
not crank the engine more than 10 seconds on
each attempt. NOTICEECB00164For maximum engine life, never accelerate
hard when the engine is cold! EBU20525ShiftingThis ATV has a 5-speed forward transmission. The
transmission allows you to control the amount of
power you have available at a given speed or for
starting, accelerating, climbing hills, etc.
To shift into neutral, release the throttle lever, ap-
ply the clutch, and then repeatedly depress the
shift pedal until it stops.
When it stops, it will be in first gear. Raise the ped-
al slightly to reach the neutral position, and then
release the clutch.
EBU20595To start out and accelerate1. Release the throttle lever, apply the front or rear brake, and then release the parking
brake.
2. Pull the clutch lever to disengage the clutch.
3. Shift into first gear, and then release the brake. NOTICE: Always close the throttle
before shifting gears, otherwise damage
to the engine and drive train may result.
[ECB01220]
1. Shift pedal
2. Neutral position
1
1
N
2 3
4
5
2
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7-3
7
4. Open the throttle gradually and at the same
time, release the clutch lever slowly.
WARNING! Opening the throttle abruptly or releasing the clutch lever too quickly
could make the ATV wheelie, which would
increase the chance of an accident, in-
cluding an overturn.
[EWB00732]
5. Once the ATV has attained adequate speed, release the throttle, and at the same time,
quickly pull in the clutch lever.
6. Shift the transmission into second gear. (Make sure not to shift the transmission into
neutral.)
7. Open the throttle part way and gradually re- lease the clutch lever.
8. Follow the same procedure when shifting to the next higher gear.EBU20653To decelerate
When slowing down or stopping, release the
throttle and apply the brakes smoothly and evenly.
As you slow down, shift to a lower gear. Be sure
that the engine has sufficiently slowed before en-
gaging a lower gear. Improper use of the brakes or shifting can cause the tires to lose traction, reduc-
ing control and increasing the possibility of an ac-
cident.
WARNING
EWB00712Make sure the engine has sufficiently slowed
before shifting to a lower gear. Engaging a low-
er gear when the engine speed is too high
could make the wheels stop rotating and lose
traction. This could cause loss of control, an
accident and injury. It could also cause engine
or drivetrain damage. NOTICEECB00181
Even with the transmission in the neutral po-
sition, do not coast for long periods of time
with the engine off, and do not tow the ATV
for long distances. The transmission is prop-
erly lubricated only when the engine is run-
ning. Inadequate lubrication may damage
the transmission.
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