Stihl KM 90 R User manual

{
STIHL KM 90 R Instruction Manual
Notice d’emploi

Original Instruction ManualPrinted on chlorine-free paper
Printing inks contain vegetable oils, paper can be recycled.
© ANDREAS STIHL AG & Co. KG, 2014
0458-465-8221-C. VA4.M13.
0000000812_011_GB
KM 90 R
English
1
{This instruction manual is protected by copyright. All rights reserved, especially the rights to reproduce, translate and process
with electronic systems.
Contents
Dear Customer,
Thank you for choosing a quality
engineered STIHL product.
It has been built using modern
production techniques and
comprehensive quality assurance.
Every effort has been made to ensure
your satisfaction and troublefree use of
the product.
Please contact your dealer or our sales
company if you have any queries
concerning this product.
Your
Dr. Nikolas Stihl
KombiSystem 2
Guide to Using this Manual 2
Safety Precautions and Working
Techniques 3
Approved KombiTools 8
Mounting the Loop Handle 9
Adjusting the Throttle Cable 10
4-MIX Engine 10
Fuel 10
Fueling 11
Starting / Stopping the Engine 12
Operating Instructions 14
Cleaning the Air Filter 14
Engine Management 15
Adjusting the Carburetor 15
Spark Arresting Screen in Muffler 15
Spark Plug 16
Rewind Starter 17
Storing the Machine 17
Inspections and Maintenance by
Dealer 18
Maintenance and Care 19
Main Parts 21
Specifications 22
Special Accessories 23
Maintenance and Repairs 23
Disposal 24
STIHL Limited Emission Control
Warranty Statement 24

KM 90 R
English
2
In the STIHL KombiSystem a number of
different KombiEngines and KombiTools
can be combined to produce a power
tool. In this instruction manual the
functional unit formed by the
KombiEngine and KombiTool is referred
to as the power tool.
Therefore, the separate instruction
manuals for the KombiEngine and
KombiTool should be used together for
the power tool.
Always read and and make sure you
understand both instruction manuals
before using your power tool for the first
time and keep them in a safe place for
future reference.
Pictograms
The meanings of the pictograms
attached to the machine are explained in
this manual.
Depending on the model concerned, the
following pictograms may be attached to
your machine.
Symbols in text
WARNING
Warning where there is a risk of an
accident or personal injury or serious
damage to property.
NOTICE
Caution where there is a risk of
damaging the machine or its individual
components.
Engineering improvements
STIHL's philosophy is to continually
improve all of its products. For this
reason we may modify the design,
engineering and appearance of our
products periodically.
Therefore, some changes, modifications
and improvements may not be covered
in this manual.
KombiSystem
.
.
.
.
002BA530 KN
+
+
Guide to Using this Manual
Fuel tank; fuel mixture of
gasoline and engine oil
Operate decompression
valve
Manual fuel pump
Operate manual fuel
pump
Tube of grease
Intake air: Summer
operation
Intake air: Winter
operation
Handle heating

KM 90 R
English
3
Observe all applicable local safety
regulations, standards and ordinances.
If you have not used this type of power
tool before: Have your dealer or other
experienced user show you how to
operate your unit or attend a special
course in its operation.
Minors should never be allowed to use a
power tool.
Keep bystanders, especially children,
and animals away from the work area.
When the power tool is not in use, shut it
off so that it does not endanger others.
Secure it against unauthorized use.
The user is responsible for avoiding
injury to third parties or damage to their
property.
Lend or rent your power tool only to
persons who are familiar with this model
and its operation – do not lend of rent
your power tool without the
KombiEngine and KombiTool instruction
manuals.
The use of noise emitting power tools
may be restricted to certain times by
national or local regulations.
To operate the power tool you must be
rested, in good physical condition and
mental health.
If you have any condition that might be
aggravated by strenuous work, check
with your doctor before operating a
power tool.
Persons with pacemakers only: The
ignition system of your power tool
produces an electromagnetic field of a
very low intensity. This field may
interfere with some pacemakers. STIHL
recommends that persons with
pacemakers consult their physician and
the pacemaker manufacturer to reduce
any health risk.
Do not operate the power tool if you are
under the influence of any substance
(drugs, alcohol) which might impair
vision, dexterity or judgment.
Use your power tool only for the
applications described in the instruction
manual of the KombiTool you are using.
Do not use your power tool for any other
purpose because of the increased risk of
accidents.
Do not operate the KombiEngine without
a properly mounted KombiTool since
this may result in damage to the
machine.
Only use KombiTools and accessories
that are explicity approved for this power
tool by STIHL or are technically
identical. It is important that you read the
chapter on "Approved KombiTools". If
you have any questions in this respect,
consult a servicing dealer. Use only high
quality tools and accessories. in order to
avoid the risk of accidents and damage
to the machine.
STIHL recommends the use of genuine
STIHL tools and accessories. They are
specifically designed to match the
product and meet your performance
requirements.
Never attempt to modify your power tool
in any way since this may increase the
risk of personal injury. STIHL excludes
all liability for personal injury and
damage to property caused while using
unauthorized attachments.
Do not use a pressure washer to clean
your power tool. The solid jet of water
may damage parts of the power tool.
Clothing and Equipment
Wear proper protective clothing and
equipment.
Safety Precautions and
Working Techniques
Special safety precau-
tions must be observed
when working with a
power tool.
Always read and and
make sure you under-
stand both instruction
manuals (KombiEngine
and KombiTool) before
using your power tool for
the first time and keep
them in a safe place for
future reference. Non-
observance of the safety
precautions may result in
serious or even fatal
injury.

KM 90 R
English
4
See also notes on "Clothing and
Equipment" in the instruction manual of
the KombiTool you are using.
Transporting the Power Tool
Always turn off the engine.
In vehicles: Properly secure your power
tool to prevent turnover, fuel spillage and
damage.
See also notes on "Transporting the
Machine" in the instruction manual of the
KombiTool you are using.
Fueling
Always shut off the engine before
refueling.
Do not fuel a hot engine – fuel may spill
and cause a fire.
Open the fuel cap carefully to allow any
pressure build-up in the tank to release
slowly and avoid fuel spillage.
Fuel your power tool only in well-
ventilated areas. If you spill fuel, wipe
the machine immediately – if fuel gets on
your clothing, change immediately.
This reduces the risk of unit vibrations
causing the fuel cap to loosen or come
off and spill quantities of fuel.
To reduce the risk of serious or fatal
burn injuries, check for fuel leakage. If
fuel leakage is found, do not start or run
the engine until leak is fixed.
Before Starting
Check that your power tool is properly
assembled and in good condition – refer
to appropriate chapters in the instruction
manuals.
–Check the fuel system for leaks,
paying special attention to visible
parts such as the tank cap, hose
connections and the manual fuel
pump (on machines so equipped). If
there are any leaks or damage, do
not start the engine – risk of fire.
Have your machine repaired by a
servicing dealer before using it
again.
–Use only an approved combination
of cutting attachment, deflector,
handle and harness. All parts must
be assembled properly and
securely.
–Slide control / stop switch must
move easily to STOP or 0.
–Smooth action of throttle trigger
lockout and throttle trigger – the
throttle trigger must return
automatically to the idle position.
–Check that the spark plug boot is
secure – a loose boot may cause
arcing that could ignite combustible
fumes and cause a fire.
–Never attempt to modify the controls
or safety devices in any way.
–Keep the handles dry and clean –
free from oil and dirt – for safe
control of the power tool.
–Adjust harness and handle to suit
your height and reach.
To reduce the risk of accidents, do not
operate your power tool if it is damaged
or not properly assembled.
If you use a shoulder strap or full
harness: Practice removing and putting
down the machine as you would in an
emergency. To avoid damage, do not
throw the machine to the ground when
practicing.
See also notes on "Before Starting" in
the instruction manual of the KombiTool
you are using.
Avoid clothing that could
get caught on branches
or brush or moving parts
of the machine. Do not
wear a scarf, necktie or
jewelry. Tie up and con-
fine long hair (e.g. with a
hair net, cap, hard hat,
etc.).
Gasoline is an extremely
flammable fuel. Keep
clear of naked flames. Do
not spill any fuel – do not
smoke.
After fueling, tighten
down the fuel tank cap as
securely as possible.

KM 90 R
English
5
Starting the Engine
Start the engine at least 3 meters from
the fueling spot, outdoors only.
Place the unit on firm ground in an open
area. Make sure you have good balance
and secure footing. Hold the unit
securely. The attachment must be clear
of the ground and all other obstructions
because it may begin to run when the
engine starts.
To reduce the risk of injury, avoid
contact with the attachment.
Do not drop start the power tool – start
the engine as described in the
instruction manual. Note that the
attachment continues to run for a short
period after you let go of the throttle
trigger – flywheel effect.
Check idle speed setting: The
attachment must be stationary when the
engine is idling with the throttle trigger
released.
To reduce the risk of fire, keep hot
exhaust gases and hot muffler away
from easily combustible materials (e.g.
wood chips, bark, dry grass, fuel).
See also notes on "Starting / Stopping
the Engine" in the instruction manual of
the KombiTool you are using.
Holding and Controlling the Power Tool
Always hold the power tool firmly with
both hands on the handles.
Make sure you always have good
balance and secure footing.
Left hand on loop handle, right hand on
control handle, even if you are left-
handed.
During Operation
In the event of impending danger or in
an emergency, switch off the engine
immediately by moving the slide control
/ stop switch to STOP or 0.
The correct engine idle speed is
important to ensure that the attachment
stops moving when you let go of the
throttle trigger. If the attachment
continues to move when the engine is
idling, have your dealer check the
machine and make proper adjustments
or repairs. Check and correct the idle
speed setting regularly. STIHL
recommends a STIHL servicing dealer.
Be particularly alert and cautious when
wearing hearing protection because
your ability to hear warnings (shouts,
alarms, etc.) is restricted.
To reduce the risk of accidents, take a
break in good time to avoid tiredness or
exhaustion.
Work calmly and carefully – in daylight
conditions and only when visibility is
good. Stay alert so as not to endanger
others.
Use your power tool only for those
applications described in the KombiTool
instruction manual.
To reduce the risk of serious or fatal
injury from breathing toxic fumes,
ensure proper ventilation when working
in trenches, hollows or other confined
locations.
To reduce the risk of accidents, stop
work immediately in the event of
nausea, headache, visual disturbances
(e.g. reduced field of vision), problems
with hearing, dizziness, deterioration in
ability to concentrate. Apart from other
possibilities, these symptoms may be
caused by an excessively high
concentration of exhaust gases in the
work area.
Operate your power tool so that it
produces a minimum of noise and
emissions – do not run the engine
unnecessarily, accelerate the engine
only when working.
To reduce the risk of fire, do not smoke
while operating or standing near your
power tool. Note that combustible fuel
vapor may escape from the fuel system.
002BA273 KN
Your power tool produces
toxic exhaust fumes as
soon as the engine is
running. These fumes
may be colorless and
odorless and contain
unburned hydrocarbons
and benzol. Never run
the engine indoors or in
poorly ventilated loca-
tions, even if your model
is equipped with a cata-
lytic converter.

KM 90 R
English
6
The dusts, vapor and smoke produced
during operation may be dangerous to
health. Wear a suitable respirator in very
dusty or smoky conditions.
If your power tool is subjected to
unusually high loads for which it was not
designed (e.g. heavy impact or a fall),
always check that it is in good condition
before continuing work – see also
"Before Starting". Check the fuel system
in particular for leaks and make sure the
safety devices are working properly. Do
not continue operating your power tool if
it is damaged. In case of doubt, consult
your servicing dealer.
Do not operate your power tool in the
starting throttle position – engine speed
cannot be controlled in this position.
Before leaving the power tool
unattended: Shut off the engine.
To reduce the risk of injury, always shut
off the engine before changing the
KombiTool or attachment.
Vibrations
Prolonged use of the power tool may
result in vibration-induced circulation
problems in the hands (whitefinger
disease).
No general recommendation can be
given for the length of usage because it
depends on several factors.
The period of usage is prolonged by:
–Hand protection (wearing warm
gloves)
–Work breaks
The period of usage is shortened by:
–Any personal tendency to suffer
from poor circulation (symptoms:
frequently cold fingers, tingling
sensations).
–Low outside temperatures.
–The force with which the handles
are held (a tight grip restricts
circulation).
Continual and regular users should
monitor closely the condition of their
hands and fingers. If any of the above
symptoms appear (e.g. tingling
sensation in fingers), seek medical
advice.
Maintenance and Repairs
Service the machine regularly. Do not
attempt any maintenance or repair work
not described in the instruction manual.
Have all other work performed by a
servicing dealer.
STIHL recommends that you have
servicing and repair work carried out
exclusively by an authorized STIHL
servicing dealer. STIHL dealers are
regularly given the opportunity to attend
training courses and are supplied with
the necessary technical information.
Only use high-quality replacement parts
in order to avoid the risk of accidents
and damage to the machine. If you have
any questions in this respect, consult a
servicing dealer.
STIHL recommends the use of original
STIHL replacement parts. They are
specifically designed to match your
model and meet your performance
requirements.
To reduce the risk of injury, always shut
off the engine before carrying out any
maintenance or repairs or cleaning the
machine. – Exception: Carburetor and
idle speed adjustments.
Do not turn the engine over on the
starter with the spark plug boot or spark
plug removed unless the slide control /
stop switch is on STOP or 0 since there
is otherwise a risk of fire from
uncontained sparking.
To reduce the risk of fire, do not service
or store your machine near open flames.
Check the fuel filler cap for leaks at
regular intervals.
Use only a spark plug of the type
approved by STIHL and make sure it is
in good condition – see "Specifications".
Inspect the ignition lead (insulation in
good condition, secure connection).
Check the condition of the muffler.
To reduce the risk of fire and damage to
hearing, do not operate your machine if
the muffler is damaged or missing. –
Do not touch a hot muffler since burn
injury will result.
Vibration behavior is influenced by the
condition of the AV elements – check the
AV elements at regular intervals.
Maintenance, replacement, or repair of
the emission control devices and
systems may be performed by any
nonroad engine repair establishment or
individual. However, if you make a
warranty claim for a component which
has not been serviced or maintained
properly or if nonapproved replacement
parts were used, STIHL may deny
coverage.

KM 90 R
English
7
For any maintenance please refer to the
maintenance chart and to the warranty
statement near the end of the instruction
manual.

KM 90 R
English
8
The following STIHL KombiTools may
be mounted on the KombiEngine:
The barrier bar supplied with the
machine must be mounted to the loop
handle – see also "Mounting the Loop
Handle".
Approved KombiTools
HT-KM
BF-KM
464BA002 KN
FCS-KM
FCB-KM
KW-KM
KB-KM
FH-KM
FS-KM FS-KM
FSB-KM BG-KM
FBD-KM
KombiTool Application
FS-KM Brushcutter with
mowing head
FS-KM Brushcutter with
grass cutting blade
FSB-KM Brushcutter with
mowing head
HL-KM 135° Hedge trimmer,
adjustable
HL-KM 0° Hedge trimmer
FH-KM 135° Power scythe
BG-KM Blower
HT-KM Pole pruner
BF-KM Pick tines
FBD-KM Redefining bed
edges
FCB-KM Lawn edging
FCS-KM Lawn edging
KB-KM Bristle brush
KW-KM PowerSweep

KM 90 R
English
9
A barrier bar is supplied with the
machine. Attach the barrier bar to the
loop handle.
NInsert square nuts (1) in the barrier
bar (2) – the holes must line up
NInsert the clamp (3) in the loop
handle (4) and position them
together on the shaft (5)
NPosition clamp (6)
NPosition barrier bar (2) – note
position!
NLine up the holes
NInsert bolts (7) in the holes – and
screw them into the barrier bar as
far as possible
NFit the loop handle (4) at a distance
of (A) approx. 20 cm (8 in) forward
of the control handle (8)
NOrient the loop handle
NTighten the bolts – lock the nuts if
necessary
The sleeve (9) is present depending on
the country and must be located
between the loop handle and control
handle.
Always leave the barrier bar attached.
Mounting the Loop Handle
2
002BA098 KN
1
1
5
4
002BA099 KN
2
3
67
A
9
8
4
002BA353 KN

KM 90 R
English
10
A properly adjusted throttle cable is the
precondition for correct operation in the
full throttle, starting throttle and idle
positions.
NAdjust the throttle cable only when
the unit is completely and properly
assembled.
NUse a suitable tool to push the slide
to the end of the slot (see
illustration).
NPress down the throttle trigger
lockout (1) and squeeze the throttle
trigger (2) (full throttle) – this sets
the throttle cable correctly.
The STIHL 4-MIX engine features
mixture lubrication and must be run on a
fuel mixture of gasoline and engine oil.
It operates otherwise on the 4-stroke
principle.
This engine is certified to operate on
unleaded gasoline and the STIHL two-
stroke engine oil at a mix ratio of 50:1.
Your engine requires a mixture of high-
quality gasoline and two-stroke air
cooled engine oil.
Use mid-grade unleaded gasoline with a
minimum octane rating of 89 ((R+M)/2)
and no more than 10% ethanol content.
Fuel with a lower octane rating may
increase engine temperatures. This, in
turn, increases the risk of piston seizure
and damage to the engine.
The chemical composition of the fuel is
also important. Some fuel additives not
only detrimentally affect elastomers
(carburetor diaphragms, oil seals, fuel
lines, etc.), but magnesium castings and
catalytic converters as well. This could
cause running problems or even
damage the engine. For this reason
STIHL recommends that you use only
high-quality unleaded gasoline!
Gasoline with an ethanol content of
more than 10% can cause running
problems and major damage in engines
and should not be used.
The ethanol content in gasoline affects
engine running speed – it may be
necessary to readjust the carburetor if
you use fuels with various ethanol
contents.
WARNING
To reduce the risk of personal injury
from loss of control and / or contact with
the running cutting tool, do not use your
Adjusting the Throttle Cable
002BA163 KN
2
1
002BA161 KN
4-MIX Engine Fuel

KM 90 R
English
11
unit with incorrect idle adjustment. At
correct idle speed, the cutting tool
should not move.
If your power tool shows an incorrect idle
adjustment, have your STIHL dealer
check your power tool and make proper
adjustments and repairs.
The idle speed and maximum speed of
the engine change if you switch from a
fuel with a certain ethanol content to
another fuel with a much higher or lower
ethanol content.
This problem can be avoided by always
using fuel with the same ethanol
content.
Use STIHL HP Ultra oil or ask your
dealer for an equivalent high quality oil
to ensure the maximum performance of
the product for the full lifetime.
To meet the requirements of EPA
40CFR90/1054 we recommend to use
STIHL HP Ultra oil.
Do not use BIA or TCW rated (two-
stroke water cooled) mix oils or other
mix oils that state they are for use in both
water cooled and air cooled engines
(e.g., outboard motors, snowmobiles,
chain saws, mopeds, etc.).
Take care when handling gasoline.
Avoid direct contact with the skin and
avoid inhaling fuel vapor. When filling at
the pump, first remove the container
from your vehicle and place the
container on the ground before filling. To
reduce the risk of sparks from static
discharge and resulting fire and/or
explosion, do not fill fuel containers that
are sitting in or on a vehicle or trailer.
The container should be kept tightly
closed in order to limit the amount of
moisture that gets into the mixture.
The machine’s fuel tank should be
cleaned as necessary.
Fuel mix ages
Only mix sufficient fuel for a few days
work, not to exceed 30 days of storage.
Store in approved fuel-containers only.
When mixing, pour oil into the container
first, and then add gasoline. Close the
container and shake it vigorously by
hand to ensure proper mixing of the oil
with the fuel.
Dispose of empty mixing-oil containers
only at authorized disposal locations.
Preparations
NBefore fueling, clean the filler cap
and the area around it to ensure that
no dirt falls into the tank.
NPosition the machine so that the
tank cap faces up.
Opening the filler cap
NTurn the cap counterclockwise until
it can be removed from the tank
opening.
NRemove the cap.
Gasoline Oil (STIHL 50:1 or equiva-
lent high-quality oils)
Liters Liters (ml)
10.02(20)
5 0.10 (100)
10 0.20 (200)
20 0.40 (400)
US gal. US fl.oz.
12.6
2 1/2 6.4
512.8
Fueling
266BA028 KN
2709BA003 KN

KM 90 R
English
12
Filling Up with Fuel
Take care not to spill fuel while fueling
and do not overfill the tank.
STIHL recommends you use the STIHL
filler nozzle for fuel (special accessory).
NFill up with fuel.
Closing the filler cap
NPlace the cap in the opening.
NTurn the cap clockwise as far as
stop and tighten it down as firmly as
possible by hand.
Controls
1Throttle trigger lockout
2Throttle lever
3Slide control
Positions of slide control
4STOP-0 – engine off – the ignition is
switched off
5F – normal run position – the engine
is running or can start
6START – the ignition is switched on
– the engine can start
Symbol on slide control
7h – stop symbol and arrow. To stop
the engine, push the slide control in
the direction of the arrow on the stop
symbol (h) to STOP-0.
Starting
NPress down the trigger lockout lever
and squeeze the throttle trigger.
Nand hold them in that position.
NMove the slide control to START
and hold it there.
NNow release the throttle trigger,
slide control and trigger lockout in
that order. This is the starting
throttle position.
NSet the choke knob (8)
2709BA004 KN
Starting / Stopping the
Engine
3
STOP
2
5
6
4
7
002BA181 KN
START
STOP-
1
249BA057 KN
9
8

KM 90 R
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13
NPress the fuel pump bulb (9) at least
five times – even if the bulb is
already filled with fuel.
Starting
NPlace the power tool on the ground
so that it rests on the machine
support: Check that the working tool
is not touching the ground or any
other obstacles – see also
"Starting / Stopping the Engine" in
the KombiTool instruction manual.
NMake sure you have a safe and
secure footing.
NHold the unit with your left hand and
press it down firmly – your thumb
should be under the fan housing.
NOTICE
Do not stand or kneel on the drive tube.
NHold the starter grip with your right
hand.
NPull the starter grip slowly until you
feel it engage and then give it a brisk
strong pull.
NOTICE
Do not pull out the starter rope all the
way – it might otherwise break.
NDo not let the starter grip snap back.
Guide it slowly back into the housing
so that the starter rope can rewind
properly.
NContinue cranking.
NAfter no more than five pulls, move
the choke knob to e.
When the engine begins to fire:
NContinue cranking.
As soon as the engine runs
NBlip the throttle trigger immediately.
The slide control moves to the
normal run position F – and the
engine settles down to idle speed.
WARNING
Make sure the carburetor is correctly
adjusted. The working tool must not
move when the engine is idling.
Your machine is now ready for
operation.
Stopping the engine
NPush the slide control in the
direction of the arrow on the stop
symbol (h) to STOP-0.
At very low outside temperatures:
As soon as the engine runs:
NBlip the throttle trigger to disengage
the starting throttle position. The
slide control moves to the normal
run position (F) – and the engine
settles down to idle speed.
NOpen the throttle slightly.
NWarm up the engine for a short
period.
If the engine does not start
Choke knob
If you did not turn the choke knob to e
quickly enough after the engine began to
fire, the combustion chamber is flooded.
gif the engine is cold
efor warm start – also use this posi-
tion if the engine has been running
but is still cold.
552BA014 KN
552BA015 KN
552BA016 KN

KM 90 R
English
14
NTurn the choke knob to e
NSet the slide control, lockout lever
and throttle trigger to the starting
throttle position.
NStart the engine by pulling the
starter rope briskly – 10 to 20 pulls
may be necessary.
If the engine still does not start
NMove the slide control to STOP-0.
NRemove the spark plug – see
"Spark Plug".
NDry the spark plug.
NCrank the engine several times with
the starter to clear the combustion
chamber.
NRefit the spark plug – see "Spark
Plug".
NMove the slide control to START.
NSet the choke knob to e – even if
the engine is cold.
NNow start the engine.
Throttle cable adjustment
NCheck adjustment of throttle cable –
see chapter on "Adjusting the
Throttle Cable".
Fuel tank run until completely dry
NAfter refueling, press the fuel pump
bulb at least five times – even if the
bulb is filled with fuel.
NSet the choke knob according to
engine temperature.
NStart the engine.
During break-in period
A factory-new machine should not be
run at high revs (full throttle off load) for
the first three tank fillings. This avoids
unnecessary high loads during the
break-in period. As all moving parts
have to bed in during the break-in
period, the frictional resistances in the
engine are greater during this period.
The engine develops its maximum
power after about 5 to 15 tank fillings.
During Operation
After a long period of full throttle
operation, allow the engine to run for a
short while at idle speed so that engine
heat can be dissipated by the flow of
cooling air. This protects engine-
mounted components (ignition,
carburetor) from thermal overload.
After Finishing Work
Storing for a short period: Wait for the
engine to cool down. Empty the fuel tank
and keep the machine in a dry place,
well away from sources of ignition, until
you need it again. For longer out-of-
service periods – see "Storing the
Machine".
If there is a noticeable loss of engine
power
NTurn the choke knob to g
NTake out the screw (1) and remove
the filter cover (2).
NClean away loose dirt from around
the filter.
NGrip the filter element (3) at the
cutout (arrow) in the filter
housing (4) and remove it.
NFit a new filter element. As a
temporary measure you can knock it
out on the palm of your hand or blow
it out with compressed air. Do not
wash.
NReplace damaged parts.
Installing the filter
NInstall the filter element in the filter
housing and fit the cover.
NInsert the screw and tighten it down
firmly.
Operating Instructions Cleaning the Air Filter
1
273BA006 KN
2
4

KM 90 R
English
15
Exhaust emissions are controlled by the
design of the fundamental engine
parameters and components (e.g.
carburation, ignition, timing and valve or
port timing) without the addition of any
major hardware.
The carburetor has been set at the
factory to provide an optimum fuel-air
mixture under most operating
conditions.
Adjusting Idle Speed
Engine stops while idling
NWarm up the engine for about
3 minutes.
NTurn the idle speed screw (LA)
slowly clockwise until the engine
runs smoothly – the cutting
attachment must not rotate.
Cutting attachment rotates when engine
is idling
NTurn the idle speed screw (LA)
counterclockwise until the cutting
attachment stops rotating and then
turn the screw about another 1/2 to
3/4 turn in the same direction.
WARNING
If the cutting attachment continues to run
when the engine is idling, have your
machine checked and repaired by your
servicing dealer.
The muffler is equipped with a spark
arresting screen.
NIf the engine is down on power,
check the spark arresting screen in
the muffler.
NWait for the muffler to cool down.
NMove the slide control to STOP-0.
NTake out the screw (1).
NTake out the screws (2) and remove
the shroud (3).
Engine Management Adjusting the Carburetor
266BA027 KN
LA
Spark Arresting Screen in
Muffler
249BA059 KN
1
2
3
2
249BA060 KN

KM 90 R
English
16
NTake out the screw (4).
NLift the spark arresting screen (5)
and pull it out.
NClean the spark arresting screen. If
the screen is damaged or heavily
carbonized, fit a new one.
NRefit the spark arresting screen.
NInsert screw and tighten it down
firmly.
NInstall the shroud.
NIf the engine is down on power,
difficult to start or runs poorly at idle
speed, first check the spark plug.
NFit a new spark plug after about 100
operating hours – or sooner if the
electrodes are badly eroded. Install
only suppressed spark plugs of the
type approved by STIHL – see
"Specifications".
Removing the spark plug
NMove the slide control to STOP-0.
NPull off the spark plug boot (1).
NUnscrew the spark plug.
Checking the spark plug
NClean dirty spark plug.
NCheck electrode gap (A) and
readjust if necessary – see
"Specifications".
NRectify the problems which have
caused fouling of the spark plug.
Possible causes are:
–Too much oil in fuel mix.
–Dirty air filter.
–Unfavorable running conditions.
WARNING
If the spark plug comes with a
detachable adapter nut (1), screw the
adapter onto the thread and tighten it
down firmly to reduce the risk of arcing
and fire.
Spark Plug
1
249BA063 KN
000BA039 KN
A
1
000BA045 KN

KM 90 R
English
17
Installing the Spark Plug
NScrew the spark plug (2) into the
cylinder and fit the boot (1) (press it
down firmly).
To help prolong the wear life of the
starter rope, observe the following
points:
NPull the starter rope only in the
direction specified.
NDo not pull the rope over the edge of
the guide bushing.
NDo not pull out the rope more than
specified.
NDo not allow the starter grip to snap
back, guide it back into the housing
slowly – see chapter on "Starting /
Stopping the Engine."
Have a damaged starter rope replaced
by your dealer before it breaks
completely. STIHL recommends that
you have servicing and repair work
carried out exclusively by an authorized
STIHL servicing dealer.
For periods of 3 months or longer
NDrain and clean the fuel tank in a
well ventilated area.
NDispose of fuel properly in
accordance with local
environmental requirements.
NRun the engine until the carburetor
is dry – this helps prevent the
carburetor diaphragms sticking
together.
NThoroughly clean the machine – pay
special attention to the air filter.
NRemove, clean and check the
attachment. Coat metal parts with
corrosion inhibiting oil.
NStore the machine in a dry and
secure location Keep out of the
reach of children and other
unauthorized persons.
2
002BA446 KN
1
Rewind Starter Storing the Machine

KM 90 R
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18
Maintenance Work
STIHL recommends that you have
servicing and repair work carried out
exclusively by an authorized STIHL
servicing dealer.
Fuel Pickup Body in Tank
NCheck the pickup body in the fuel
tank every year and have it replaced
if necessary.
The pickup body should be positioned in
the area of the tank shown in the
illustration.
Inspections and Maintenance
by Dealer
465BA002 KN
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