2009 YAMAHA YFM90R engine

4-2
4
Handlebar switches Engine stop switch “ENG. STOP”
Set this switch to “RUN” 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 situation. The
engine will not start or run when this switch is set
to “OFF”.
Start switch “START”
Push this switch to crank the engine with the start-
er.
See the starting instructions on page 6-1 prior
to starting the engine.
1
2
1. Engine stop switch “ENG. STOP”
2. Start switch “START”

4-3
4
Throttle lever Once the engine is running, movement of the throt-
tle lever 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 hand is removed from
the throttle lever.
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.
Speed limitersYour ATV was delivered with two speed limiter
devices. 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 installed
to limit the amount of speed available while they learn.
1. Throttle lever
1

WARNING
Malfunction of the throttle could make it diffi-
cult to speed up or slow down when you need
to. This could cause an accident. Check the op-
eration of the throttle lever before you start the
engine. If the throttle does not work smoothly,
check for the cause. Correct the problem be-fore riding the ATV or consult a Yamaha dealer.

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44
The 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 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.Vehicle 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 available and the
maximum speed of the ATV, turn the adjusting
screw in direction (b).
(b)
(a)
1 2
3. Tighten the locknut.2. Adjusting screw1. Locknut
3. No more than 11 mm (0.4 in)
3

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4

WARNING
Improper adjustment of the speed limiter and
throttle could cause throttle cable damage or
improper throttle operation. You could lose
control, have an accident or be injured. Do not
turn the adjusting screw out more than 5 mm
(0.2 in).Engine speed limiter plate
TIPStore the speed limiter plate with the owner’s manual
so that it is readily available whenever you want to
reduce the top engine speed.
With this plate installed, the engine speed is limited
to 4800 r/min. With this plate removed, top engine
speed (8000 r/min) is available.
Remove the plate as follows.
1. Remove the seat. (See page 4-11.)
3. Pull the plate out of its case. 4. Tighten the screw.
2. Loosen the screws.
5. Install the seat.
1. Speed limiter plate
2. Screws
21

4-7
Parking brake Use the parking brake before starting the engine or
parking the ATV, especially on a slope. Apply the
front bake lever and push down the lock button to
apply the parking brake. Squeeze the front brake
lever to release the parking brake.1. Parking brake lock button

4
1
WARNING
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 brakesprematurely.

4-9
N O T I C EUse only unleaded gasoline. The use of leaded
gasoline will cause severe damage to internal
engine parts, such as the valves and pistonrings, as well as to the exhaust system.
4
WARNING
Do not overfill the fuel tank. Fuel expands
when it heats up. If the fuel tank is overfilled,
fuel could spill out due to heat from the en-
gine or the sun.Be careful not to spill fuel, especially on the
engine or exhaust pipe which can cause a
fire and severe injury. Wipe up any spilled
fuel immediately.Do not refuel right after the engine has been
running and is still very hot.Be sure the fuel tank cap is closed securely.

Fuel cock The fuel cock supplies fuel from the tank to the car-
buretor while also filtering it.
The fuel cock lever positions are explained as fol-
lows and shown in the illustrations.1. Lever positioned over “OFF”
RES
OFFWith the fuel cock lever in this position, fuel will not
flow. Always turn the fuel cock lever to this position
when the engine is not running.ONRES
5
1. Lever positioned over “RES”
1. Lever positioned over “ON” 4-10 With the fuel cock lever in this position, fuel flows
to the carburetor. Turn the fuel cock lever to this
position when starting the engine and riding.
This indicates reserve. With the fuel cock lever in
this position, the fuel reserve is made available.
Turn the fuel cock lever to this position if you run
out of fuel while riding. When this occurs, refuel as
soon as possible and be sure to turn the fuel cock
lever back to “ON”!
OFF
ON
RES
FUEL
1OFF
OFF
ON
RES
FUELRES
1
OFF
ON
RES
FUEL
1
ON
4

4-11
ChokeThe choke is used to start a cold engine.
Move the choke in direction (a) to turn on the
choke.
Move the choke in direction (b) to turn off the
choke.
See the “Starting a cold engine” section on page
6-1 for proper operation.1. Fully open “ON”
2. Half open (warming up position)
3. Closed “OFF”
4. Choke
1 2 3
(a)
(b)
4
4
SeatTo remove the seat
Pull the seat lock lever upward and pull up the seat
at the rear.
1
1. Seat lock lever