2018 YAMAHA YZ85 engine

Instrument and control functions
4-6
4
EAU41362
Fuel tank breather hose
Before operating the motorcycle:
 Check the fuel tank breather hose
connection.
 Check the fuel tank breather hose
for cracks or damage, and replace
it if necessary.
 Make sure that the end of the fuel
tank breather hose is not blocked,
and clean it if necessary.
TIP
If the fuel tank breather hose falls out,
reinstall it on the fuel tank cap with the
arrow mark on the one-way valve
pointed downward as shown.
EAU41281
Fuel cock
The fuel cock supplies fuel from the
tank to the carburetor while filtering it
also.
The fuel cock has two positions:
OFF
With the lever in this position, fuel will
not flow. Always return the lever to this
position when the engine is not run-
ning.
ON
With the lever in this position, fuel flows
to the carburetor. Normal riding is done
with the lever in this position.
1. Fuel tank breather hose
2. One-way valve
1. Arrow mark positioned over “OFF”
1. Arrow mark positioned over “ON”
U1SN86E0.book Page 6 Wednesday, June 7, 2017 10:21 AM

Instrument and control functions
4-7
4
EAU13641
Starter (choke) kno b
Starting a cold engine requires a richer
air-fuel mixture, which is supplied by
the starter (choke).
Move the knob in direction (a) to turn
on the starter (choke).
Move the knob in direction (b) to turn
off the starter (choke).
EAU13651
Kickstarter
To start the engine, fold out the kick-
starter lever, move it down lightly with
your foot until the gears engage, and
then push it down smoothly but force-
fully. This model is equipped with a pri-
mary kickstarter, allowing the engine to
be started in any gear if the clutch is
disengaged. However, shifting the
transmission into the neutral position
before starting is recommended.
1. Starter (choke) knob1. Kickstarter lever
U1SN86E0.book Page 7 Wednesday, June 7, 2017 10:21 AM

Operation and important ri din g points
6-1
6
EAU15952
Read the Owner’s Manual carefully to
become familiar with all controls. If
there is a control or function you do not
understand, ask your Yamaha dealer.
WARNING
EWA10272
Failure to familiarize yourself with
the controls can lead to loss of con-
trol, which coul d cause an acci dent
or injury.
EAU41308
Startin g an d warmin g up a
col d en gine
1. Turn the fuel cock lever to “ON”.
2. Shift the transmission into the
neutral position.
3. Turn the starter (choke) on and completely close the throttle. (See
page 4-7.)
4. Start the engine by pushing the kickstarter lever down.
5. When the engine is warm, turn the starter (choke) off.
TIP
The engine is warm when it responds
quickly to the throttle with the starter
(choke) turned off.
NOTICE
ECA11043
For maximum en gine life, never ac-
celerate har d when the en gine is
col d!
U1SN86E0.book Page 1 Wednesday, June 7, 2017 10:21 AM

Operation and important rid ing points
6-2
6
EAU16661
Startin g a warm en gine
Follow the same procedure as for
starting a cold engine with the excep-
tion that the starter (choke) is not re-
quired when the engine is warm.
Instead, start the engine with the throt-
tle slightly open.
TIP
If the engine does not start after sever-
al kicks, try again with the throttle 1/4
to 1/2 open.
EAU16673
Shiftin g
Shifting gears lets you control the
amount of engine power available for
starting off, accelerating, climbing hills,
etc.
The gear positions are shown in the il-
lustration.
TIP
To shift the transmission into the neu-
tral position, press the shift pedal down
repeatedly until it reaches the end of its
travel, and then slightly raise it.
NOTICE
ECA10261
Even with the transmission in
the neutral position, d o not
coast for lon g period s of time
with the en gine off, an d d o not
tow the motorcycle for lon g d is-
tances. The transmission is
properly lu bricated only when
the en gine is runnin g. Ina de-
quate lu brication may damag e
the transmission.
 Always use the clutch while
chan gin g g ears to avoi d d am-
a g in g the en gine, transmission,
1. Shift pedal
2. Neutral position
U1SN86E0.book Page 2 Wednesday, June 7, 2017 10:21 AM

Operation and important ri din g points
6-3
6
an
d d rive train, which are not
d esi gne d to withstan d the
shock of force d shifting .
EAU16691To start out an d accelerate
1. Pull the clutch lever to disengage the clutch.
2. Shift the transmission into first gear.
3. Open the throttle gradually and si- multaneously release the clutch
lever slowly.
4. Once the motorcycle has reached a speed high enough to change
gears, close the throttle, and at the
same time, quickly pull the clutch
lever in.
5. Shift the transmission into second gear. (Make sure not to shift the
transmission into the neutral posi-
tion.)
6. Open the throttle halfway and gradually release the clutch lever.
7. Follow the same procedure when
shifting to the next gear.
EAU16711To decelerate
1. Close the throttle and apply both the front and the rear brakes to
slow the motorcycle.
2. Downshift through the gears and shift the transmission into the neu-
tral position when the motorcycle
is almost completely stopped.
EAU41505
Engine break-in
WARNING
EWA10322
Failure to properly maintain the vehi-
cle or performin g maintenance ac-
tivities incorrectly may increase
your risk of injury or death durin g
service or while usin g the vehicle. If
you are not familiar with vehicle ser-
vice, have a Yamaha d ealer perform
service.
1. Before starting the engine, fill the fuel tank with a break-in oil-fuel
mixture as follows.
2. Start and warm up the engine. Check the operation of the con-
trols and the engine stop switch.
(See page 4-1.)
3. Operate the motorcycle in the low- er gears at moderate throttle
openings for five to eight minutes.
Stop the engine and check the
spark plug condition (see page
7-6); it will show a rich condition
during break-in.
4. Allow the engine to cool. Restart the engine and operate the motor-
cycle as in the step above for five
minutes. Then, very briefly shift to
the higher gears and check the
full-throttle response. Stop the en-
gine and check the spark plug.
5. After again allowing the engine to cool, restart and run the motorcy-
cle for five more minutes. Full
throttle and the higher gears may
Recommen ded 2-stroke en gine oil:
See page 9-1.
Mixin g ratio ( gasoline to oil):
15:1
U1SN86E0.book Page 3 Wednesday, June 7, 2017 10:21 AM

Operation and important rid ing points
6-4
6 be used, but sustained full-throttle
operation should be avoided.
Stop the engine and check the
spark plug again.
6. Allow the engine to cool, remove the cylinder head and cylinder,
and inspect the piston and cylin-
der. Remove any high spots on
the piston with #600-grit wet
sandpaper. Clean all components
and carefully reassemble the cyl-
inder head and cylinder.
7. Drain the break-in oil-fuel mixture from the fuel tank and refill with
the specified mix. (See page 4-4.)
8. Start the engine and check the op- eration of the motorcycle through-
out its entire operating range.
Stop the engine and check the
spark plug condition. Restart the
motorcycle and ride it for about 10
to 15 more minutes. The motorcy-
cle will now be ready to ride nor-
mally.
After the engine break-in period, thor-
oughly check the motorcycle for loose
parts, oil leakage and any other prob-
lems. Be sure to inspect and make ad-
justments thoroughly, especially cable
and drive chain slack and loose
spokes. In addition, check all fittings
and fasteners for looseness, and tight-
en if necessary.
NOTICE
ECA15561
 When any of the following parts
have been replaced , they must
b e broken in.
Cylin der or crankshaft:
A bout one hour of b reak-in op-
eration is necessary. Piston, rin
gs or transmission
g ears:
These parts require a bout 30
minutes of b reak-in operation at
half-throttle or less. O bserve the
con dition of the en gine carefully
d urin g operation.
 If any en gine trou ble shoul d oc-
cur durin g the en gine break-in
perio d, imme diately have a
Yamaha dealer check the vehi-
cle.
U1SN86E0.book Page 4 Wednesday, June 7, 2017 10:21 AM

Operation and important ri din g points
6-5
6
EAU17192
Parkin g
When parking, stop the engine, and
then turn the fuel cock lever to “OFF”.
WARNING
EWA10312
Since the en gine an d exhaust
system can become very hot,
park in a place where ped estri-
ans or chil dren are not likely to
touch them and b e burne d.
 Do not park on a slope or on soft
groun d, otherwise the vehicle
may overturn, increasin g the
risk of a fuel leak an d fire.
 Do not park near g rass or other
flammab le materials which
mi ght catch fire.
U1SN86E0.book Page 5 Wednesday, June 7, 2017 10:21 AM

Periodic maintenance an d a djustment
7-6
7
EAU19614
Checkin g the spark plu g
The spark plug is an important engine
component, which is easy to check.
Since heat and deposits will cause any
spark plug to slowly erode, the spark
plug should be removed and checked
in accordance with the periodic main-
tenance and lubrication chart. In addi-
tion, the condition of the spark plug
can reveal the condition of the engine.
To remove the spark plu g
1. Remove the spark plug cap.
2. Remove the spark plug as shown, with a spark plug wrench available
at a Yamaha dealer. To check the spark plu
g
1. Check that the porcelain insulator around the center electrode of the
spark plug is a medium-to-light
tan (the ideal color when the vehi-
cle is ridden normally).
TIP
If the spark plug shows a distinctly dif-
ferent color, the engine could be oper-
ating improperly. Do not attempt to
diagnose such problems yourself. In-
stead, have a Yamaha dealer check
the vehicle.
2. Check the spark plug for electrodeerosion and excessive carbon or
other deposits, and replace it if
necessary.
3. Measure the spark plug gap with a wire thickness gauge and, if nec-
essary, adjust the gap to specifi-
cation.
1. Spark plug cap
1. Spark plug wrench
Specified spark plu g:
NGK/BR10EG
1. Spark plug gap
Spark plu g g ap:
0.5–0.6 mm (0.020–0.024 in)
U1SN86E0.book Page 6 Wednesday, June 7, 2017 10:21 AM