Stihl HL 90 User manual

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STIHL HL 90 Instruction Manual
Notice d’emploi

GInstruction Manual
1 - 28
FNotice d’emploi
29 - 61

Original Instruction ManualPrinted on chlorine-free paper
Printing inks contain vegetable oils, paper can be recycled.
© ANDREAS STIHL AG & Co. KG, 2010
0458-445-8221-B. M0-25.M10.PM.
0000003884_001_GB
HL 90 K
English
1
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Contents
Dear Customer,
Thank you for choosing a quality
engineered STIHL product.
This machine 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 machine.
Please contact your dealer or our
sales company if you have any
queries concerning your machine.
Your
Hans Peter Stihl
Guide to Using this Manual 2
Safety Precautions and Working
Techniques 2
Using the Unit 7
Mounting the Gearbox 8
Adjusting the Throttle Cable 9
4-MIX Engine 9
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 16
Checking the Spark Plug 17
Lubricating the Gearbox 18
Replacing the Starter Rope and
Rewind Spring 19
Sharpening Instructions 21
Storing the Machine 21
Maintenance and Care 22
Main Parts 24
Specifications 25
Special Accessories 26
Maintenance and Repairs 26
STIHL Limited Emission Control
Warranty Statement 27

HL 90 K
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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
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.
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 power tool 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.
Guide to Using this Manual
Fuel tank; fuel mixture of
gasoline and engine oil
Operate manual fuel
pump
Filler hole for gear
lubricant
Blade lock
Rotating handle
Warning where there is a risk of
an accident or personal injury or
serious damage to property.
Caution where there is a risk of
damaging the machine or its
individual components.
Safety Precautions and
Working Techniques
Because a hedge trim-
mer is a high-speed, fast-
cutting power tool with
very sharp cutting blades
and a long reach, special
safety precautions must
be observed during
operation.
It is important you read
and understand the
instruction manual before
first use and keep the
manual in a safe place for
future reference. Non-
observance of the safety
precautions may result in
serious or even fatal
injury.

HL 90 K
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Do not lend or rent your power tool
without the instruction manual. Be sure
that anyone using it understands the
information contained in this manual.
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. To
reduce health risks, STIHL recommends
that persons with pacemakers consult
their physician and the pacemaker
manufacturer before operating this tool.
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 hedge trimmer only for cutting
hedges, shrubs, scrub and similar
materials.
It must not be used for any other
purpose because of the increased risk of
accidents and damage to the machine.
Never attempt to modify your power tool
in any way since this may result in
accidents or damage to the machine.
Only use parts and accessories that are
explicity approved for this power tool by
STIHL or are technically identical. If you
have any questions in this respect,
consult a servicing dealer. Use only high
quality parts and accessories in order to
avoid the risk of accidents and damage
to the machine.
STIHL recommends the use of original
STIHL replacement parts. They are
specifically designed to match your
model 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
the power tool. The solid jet of water
may damage parts of the power tool.
Do not spray the power tool with water.
Clothing and Equipment
Wear proper protective clothing and
equipment.
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 confine long hair
(e.g. with a hair net, cap, hard hat, etc.).
Wear hearing protection, e.g. earplugs
or ear muffs.
STIHL offers a comprehensive range of
personal protective clothing and
equipment.
Transporting the Power Tool
Always turn off the engine.
Always fit the blade scabbard before
carrying your hedge trimmer short
distances.
Carry the power tool properly balanced
by the drive tube – cutting blades behind
you.
Clothing must be sturdy
but allow complete free-
dom of movement. Wear
snug-fitting clothing, an
overall and jacket combi-
nation, do not wear a
work coat.
Wear steel-toed safety
boots with non-slip soles.
Wear a safety hard hat
where there is a danger
of head injuries from fall-
ing objects. Wear safety
glasses.
Wear heavy-duty gloves.
002BA247 KN

HL 90 K
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To reduce the risk of serious burn
injuries, avoid touching hot parts of the
machine, including the gearbox housing.
Transporting in a vehicle: Properly
secure your power tool to prevent
turnover, fuel spillage and damage.
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.
Your power tool comes standard with
either a screw-type or bayonet-type fuel
cap.
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
manual.
–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.
–Cutting blades securely mounted
and in good condition (clean, move
freely, not warped), properly
sharpened and thoroughly sprayed
with STIHL resin solvent (lubricant).
–Never attempt to modify the controls
or the safety devices in any way.
–Keep the handles dry and clean –
free from oil and dirt – for safe
control of the power tool.
To reduce the risk of personal injury,
do not operate your power tool if it is
damaged or not properly assembled.
Starting the Engine
Start the engine at least 3 meters from
the fueling spot, outdoors only.
Place the power tool on firm ground in
an open area. Make sure you have good
balance and secure footing. Hold the
power tool securely. The cutting blades
must be clear of the ground and all other
obstructions because they may begin to
run when the engine starts.
Your power tool is designed to be
operated by one person only. Do not
allow other persons in the work area –
even when starting.
To reduce the risk of injury, avoid
contact with the cutting blades.
Do not drop start the power tool – start
the engine as described in the
instruction manual. Note that the cutting
blades continue to run for a short period
after you let go of the throttle trigger
(flywheel effect).
Check idle speed setting: The cutting
blades must not move 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).
Holding and Controlling the Power
Tool
Always hold the power tool firmly with
both hands on the handles.
Gasoline is an
extremely flammable
fuel. Keep clear of naked
flames. Do not spill any
fuel – do not smoke.
After fueling, tighten
down the screw-type fuel
cap as securely as
possible.
Insert the fuel cap with
hinged grip (bayonet-type
cap) correctly in the
opening, turn it clockwise
as far as stop and fold the
grip down.

HL 90 K
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Make sure you have firm and secure
footing and hold the power tool so that
the cutting blades are always away from
your body.
Right hand on control handle, left hand
on handle hose on drive tube, even if
you are left-handed. Wrap your fingers
and thumbs around the handles.
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 0or STOP.
To reduce the risk
of injury from
moving blades or
falling cuttings, do
not allow
bystanders within
5 meters of your own position. To reduce
the risk of damage to property, also
maintain this distance from other objects
(vehicles, windows).
Watch the cutting blades at all times –
do not cut areas of the hedge that you
cannot see.
Be extremely careful when cutting tall
hedges, check the other side of the
hedge before starting work.
Make sure the idle speed setting is
correct. The cutting blades must not run
when the engine is idling with the throttle
trigger released. Check and correct the
idle speed setting at regular intervals. If
the cutting blades still run, have your
dealer check your machine and make
proper adjustments or repairs.
Note that the cutting blades continue to
run for a short period after you let go of
the throttle trigger (flywheel effect).
Take special care in slippery conditions
– damp, snow, ice, on slopes or uneven
ground.
Clear away fallen branches, scrub and
cuttings.
Watch out for obstacles: Roots, tree
stumps or holes which could cause you
to trip or stumble.
Make sure you always have good
balance and secure footing.
When working at heights:
–Always use a lift bucket
–Never work on a ladder or in a tree
–Never work on an insecure support
–Never operate your power tool with
one hand
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.
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.
This power tool is not
insulated against electric
shock. To reduce the
risk of electrocution,
keep well clear of electric
power lines.
002BA246 KN
5m (17ft)
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.

HL 90 K
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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.
The dusts, vapor and smoke produced
during operation may be dangerous to
health. If the work area is very dusty or
smoky, wear a respirator.
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, have the
machine checked by your servicing
dealer.
Do not operate your power tool in the
starting throttle position – engine speed
cannot be controlled in this position.
Inspect the hedge and work area to
avoid damaging the cutting blades:
–Remove stones, rocks, pieces of
metal and other solid objects.
–When working close to the ground,
make sure that no sand, grit or
stones get between the blades.
–Take particular care when cutting
hedges next to or against wire
fences.
To avoid the risk of electrocution, do
not touch electric power lines – never cut
through electric power lines.
Opening the throttle while the blades are
blocked increases the load and reduces
engine speed. The clutch then slips
continuously and this causes
overheating and damage to important
components (e.g. clutch, polymer
housing components) – and this can
increase the risk of injury from the
blades moving while the engine is idling.
If the hedge is very dusty or dirty, spray
the blades with STIHL resin solvent from
time to time during cutting. This helps
reduce blade friction as well as the
aggressive effects of sap and the build-
up of dirt particles.
Before leaving the power tool
unattended: Shut off the engine.
Check the cutting blades at regular short
intervals during operation or
immediately if there is a noticeable
change in cutting behavior:
–Stopping the engine
–Wait until the cutting blades have
come to a complete standstill.
–Check condition and tightness, look
for cracks.
–Check sharpness.
To reduce the risk of fire, always clean
plant residue, chips, leaves and excess
lubricant off the engine and muffler.
After Finishing Work
Always clean dust and dirt off the
machine – do not use any grease
solvents for this purpose.
Spray the blades with STIHL resin
solvent. Run the motor briefly so that the
solvent is evenly distributed.
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
The gearbox becomes
hot during operation. To
reduce the risk of burn
injury, do not touch the
gearbox housing.
Do not touch the cutting
blades while the engine is
running. If the cutting
blades become jammed
by thick branches or
other obstructions, switch
off the engine immedi-
ately before attempting to
free the blades.

HL 90 K
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7
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 genuine
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 0since 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.
For any maintenance please refer to the
maintenance chart and to the warranty
statement near the end of the instruction
manual.
Cutting Season
Observe country-specific or municipal
rules and regulations for cutting hedges.
Do not use your hedge trimmer during
rest periods cutomary in the
neighborhood.
Preparations
Use lopping shears to cut out thick
branches first.
Cutting Sequence
Cut the sides of the hedge first, then the
top.
If a radical cut is necessary, cut a little at
a time in several stages.
Recommendation:
Only cut hedges that are no more than
chest height.
Disposal
Do not throw cuttings into the garbage
can – they can be composted!
Using the Unit

HL 90 K
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Vertical cut
Swing the cutter bar up and down in an
arc as you move along the hedge – use
both sides of the cutting blades.
Any working position above head height
is tiring. To minimize the risk of
accidents, work in such positions for
short periods only.
Horizontal cut
Hold the cutter bar at an angle of 0° to
10° as you swing the hedge trimmer
horizontally.
Swing the cutter bar in an arc towards
the outside of the hedge so that the
cuttings are swept to the ground.
NPull the protective cap off the end of
the drive tube.
The plug may come out of the drive tube
when you pull off the cap. Push it back
into the drive tube as far as stop.
445BA001 KN
445BA007 KN
445BA002 KN
Mounting the Gearbox
413BA014 KN
002BA248 KN

HL 90 K
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NLoosen the clamp screws (1).
NPush the gearbox (2) onto the drive
tube (3) – turn it back and forth at
the same time until the end of the
drive tube is no longer visible in the
slot (arrow) – then push fully home
as far as stop.
NLine up the gearbox on the drive
tube so that the machine support on
the engine points down and the
blades are horizontal.
NTighten down the clamp screws (1)
firmly.
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.
3
1
1
2
445BA003 KN
Adjusting the Throttle
Cable
002BA163 KN
2
1
002BA161 KN
4-MIX Engine

HL 90 K
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This engine is certified to operate on
unleaded gasoline and with the mix ratio
50:1.
Your engine requires a mixture of high-
quality premium gasoline and high-
quality two-stroke air-cooled engine oil.
Use premium branded unleaded
gasoline with a minimum octane rating
of 89 RON.
Note: Models equipped with a catalytic
converter require unleaded gasoline. A
few tankfuls of leaded gasoline can
reduce the efficiency of the catalytic
converter by more than 50%.
Fuel with a lower octane rating may
result in preignition (causing "pinging")
which is accompanied by an increase in
engine temperature. This, in turn,
increases the risk of the 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 as
well. This could cause running problems
or even damage the engine. For this
reason it is essential that you use only
high-quality fuels!
Fuels with different percentages of
ethanol are being offered. Ethanol can
affect the running behaviour of the
engine and increase the risk of lean
seizure.
Gasoline with an ethanol content of
more than 10% can cause running
problems and major damage in engines
with a manually adjustable carburetor
and should not be used in such engines.
Engines equipped with M-Tronic can be
run on gasoline with an ethanol content
of up to 25% (E25).
Use only STIHL two-stroke engine oil or
equivalent high-quality two-stroke air-
cooled engine oils for mixing.
We recommend STIHL 50:1 two-stroke
engine oil since it is specially formulated
for use in STIHL engines.
Do not use BIA or TCW (two-stroke
water cooled) mix oils!
Use only STIHL 50:1 heavy-duty
engine oil or an equivalent quality two-
stroke engine oil for the fuel mix in
models equipped with a catalytic
converter.
Take care when handling gasoline.
Avoid direct contact with the skin and
avoid inhaling fuel vapour.
The canister should be kept tightly
closed in order to avoid any moisture
getting into the mixture.
The fuel tank and the canister in which
fuel mix is stored should be cleaned
from time to time.
Fuel mix ratio
Only mix sufficient fuel for a few days
work, not to exceed 3 months of storage.
Store in approved safety fuel-canisters
only. When mixing, pour oil into the
canister first, and then add gasoline.
Dispose of empty mixing-oil canisters
only at authorized disposal locations.
Fuel Examples
Gasoline Oil (STIHL 50:1 or equiva-
lent high-quality oils)
liters liters (ml)
1 0.02 (20)
5 0.10 (100)
10 0.20 (200)
15 0.30 (300)
20 0.40 (400)
25 0.50 (500)

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Preparations
NBefore fueling, clean the filler cap
and the area around it so that dirt
cannot fall into the tank.
NAlways position the machine so that
the filler cap is facing upwards.
A number of different filler caps are
installed as standard at the factory.
Cliplock filler cap (bayonet-type)
Threaded filler cap
Opening the cliplock filler cap
NSwing the clip into an upright
position
NTurn the cap counterclockwise
(approx. 1/4 turn)
NRemove the filler cap
Refueling
Take care not to spill fuel while fueling
and do not overfill the tank. STIHL
recommends use of the STIHL filling
system (special accessory).
Closing the cliplock filler cap
NPosition the cap with the clip in an
upright position; the markings must
line up
NTurn cap clockwise as far as it will
go (approx. 1/4 turn)
NFold the cliplock down so that it is
flush with the surface
If the cliplock is not flush with the surface
and the lug on the clip does not engage
entirely in the recess (arrow), the cap is
not properly closed and the steps
described above must be repeated.
Fueling
002BA420 KN
002BA418 KN
002BA419 KN
249BA053 KN
249BA054 KN
249BA055 KN
249BA056 KN

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Opening the threaded filler cap
NTurn the cap counterclockwise until
it can be removed from the tank
opening
NRemove the filler cap
Refueling
Take care not to spill fuel while fueling
and do not overfill the tank. STIHL
recommends use of the STIHL filling
system (special accessory).
Closing the threaded filler cap
NPosition cap
NTurn the cap clockwise as far as it
will go and tighten it as firmly as
possible by hand
Controls
1Throttle trigger lockout
2Throttle trigger
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
6 START – 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 the Engine
NPress down the trigger lockout lever
and squeeze the throttle trigger.
NHold both levers in this 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):
200BA421 KN
200BA422 KN
Starting / Stopping the
Engine
3
STOP
2
5
6
4
7
002BA181 KN
START
STOP-
1
249BA057 KN
9
8

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NPress the fuel pump bulb (9) at least
five times – even if the bulb is
already filled with fuel.
Starting
NPlace the unit on the ground: It must
rest securely on the engine support
and the gearbox.
NRemove the blade scabbard. Check
that the cutting blades are not
touching the ground of any other
obstacles. If necessary, rest the
gearbox on a raised support (e.g.
mound, brick or something similar).
NMake sure you have a firm footing.
NHold the unit with your left hand and
press it down firmly – your thumb
should be under the fan housing.
NPull the starter grip slowly with your
right hand until you feel it engage
and then give it a brisk strong pull.
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 until the engine
fires.
When the engine begins to fire or
after no more than five pulls:
NTurn the choke knob to e
NContinue cranking.
As soon as the engine runs
NBlip the throttle trigger. The slide
control moves to the normal run
position F– and the engine settles
down to idle speed.
Make sure the carburetor is correctly
adjusted. The cutting blades must not
move when the engine is idling.
Your machine is now ready for
operation.
Shut off the engine
NPush the slide control in the
direction of the arrow on the stop
symbol (h) to STOP-0.
Other hints on starting
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 briefly.
If the engine does not start
If you did not turn the choke knob to e
quickly enough after the engine began to
fire, the combustion chamber is flooded.
NTurn the choke knob to e
NSet the slide control, Throttle trigger
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.
NPull off the spark plug boot (10).
NUnscrew and dry off the spark plug.
gIf the engine is cold
efor warm start – also use this posi-
tion if the engine has been running
but is still cold.
445BA004 KN
445BA005 KN
Do not stand or kneel on the drive
tube since it will otherwise be
permanently bent and damaged.
Do not pull out the starter rope all
the way – it might otherwise
break.
10
249BA058 KN

HL 90 K
English
14
NOpen the throttle wide.
NCrank the engine several times with
the starter to clear the combustion
chamber.
NRefit the spark plug.
NConnect the spark plug boot (press
it down firmly).
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".
If fuel tank has been run completely
dry and then refueled
NPress the fuel pump bulb at least
five times – even if the bulb is filled
with fuel.
NSet the choke knob according to
engine temperature.
NNow start 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 perionds – 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

HL 90 K
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 comes from the factory
with a standard setting.
This setting provides an optimum fuel-air
mixture under most operating
conditions.
With this carburetor it is only possible to
adjust the high speed and low speed
screws within fine limits.
Standard Setting
NStopping the engine
NInspect the cutting blades and clean
if necessary (they must be clean,
move freely and not be warped).
NCheck that the throttle cable is
properly adjusted – readjust if
necessary – see chapter on
"Adjusting the Throttle Cable".
NCheck the spark arresting screen
(not in all versions) and clean or
replace as necessary.
NCheck the air filter and clean or
replace as necessary.
NCarefully turn both adjusting screws
counterclockwise as far as stop.
High speed screw (H) is open a 3/4 turn,
and the low speed screw (L) is open a
3/4 turn.
NStart and warm up the engine.
NAdjust idle speed with the idle speed
screw (LA) so that the cutting
blades do not run.
Fine Tuning
A slight correction of the setting of the
high speed screw (H) may be necessary
if engine power is not satisfactory when
operating at high altitude or at sea level.
NTurn the high speed screw (H)
about one quarter turn for every
1000m change in altitude.
NCarry out the standard setting
without disturbing the high speed
screw (H).
Engine Management Adjusting the Carburetor
249BA051 KN

HL 90 K
English
16
NWarm up the engine for about 3
minutes.
NOpen the throttle wide.
At high altitude
NTurn the high speed screw (H)
clockwise (leaner), no further than
stop, until there is no noticeable
increase in engine speed.
At sea level
NTurn the high speed screw (H)
counterclockwise (richer), no further
than stop, until there is no further
noticeable increase in engine
speed.
It is possible that maximum engine
speed may be reached with the standard
setting in each case.
Readjust idle
It is usually necessary to change the
setting of the idle speed screw (LA) after
every correction to the low speed
screw (L).
NWarm up the engine for about 3
minutes.
Engine stops while idling
NTurn the idle speed screw (LA)
slowly clockwise until the engine
runs smoothly – the cutting blades
must not run.
Cutting blades run when engine is
idling
NTurn the idle speed screw (LA)
counterclockwise until the cutting
blades stop running and then turn
the screw about another 1/2 to
3/4 turn in the same direction.
Erratic idling behavior, engine stops
even though setting of LA-screw has
been corrected, poor acceleration
Idle setting is too lean
NTurn the low speed screw (L)
counterclockwise, no further than
stop, until the engine runs and
accelerates smoothly.
Erratic idling behavior
Idle setting is too rich
NTurn the low speed screw (L)
clockwise, no further than stop, until
the engine runs and accelerates
smoothly.
If 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).
NTake out the screw (4).
If the cutting blades continue to
run when the engine is idling,
have your machine checked and
repaired by your servicing dealer.
Spark Arresting Screen in
Muffler
249BA059 KN
1
2
3
2
249BA060 KN

HL 90 K
English
17
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 the screw and tighten it down
firmly.
NFit the shroud.
If the engine is down on power, difficult
to start or runs poorly at idle speed, first
check the spark plug.
NRemove the spark plug, see
"Starting / Stopping the Engine".
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.
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".
To reduce the risk of arcing and fire
If the spark plug comes with a
detachable adapter nut:
NScrew the adapter nut (1) onto the
thread and tighten it down firmly.
Checking the Spark Plug
000BA002 KN
1
000BA045 KN

HL 90 K
English
18
On all spark plugs
NAlways press the boot (2) firmly on
to the spark plug (3).
Blade drive gear
Lubricate the blade drive gear with
STIHL gear lubricant for hedge trimmers
– see "Special Accessories".
NCheck the lubricant level regularly,
about every 25 hours of operation.
Unscrew the filler plug (1).
NScrew the tube of grease into the
filler hole.
NSqueeze up to 5 g grease into the
gearbox.
NUnscrew the tube of grease from the
filler hole.
NRefit the filler plug and tighten it
down firmly.
Angle drive
Lubricate the angle drive with STIHL
gear lubricant for brushcutters – see
"Special Accessories".
NCheck the lubricant level at regular
intervals of about every 25 hours of
operation. Unscrew the filler
plug (2) – if no grease can be seen
on the inside of the filler plug, screw
the tube of grease into the filler hole.
NSqueeze up to 5 g grease into the
gearbox.
NUnscrew the tube of grease from the
filler hole.
NRefit the filler plug and tighten it
down firmly.
3
002BA178 KN
2
Lubricating the Gearbox
Do not completely fill the gearbox
with grease.
Do not completely fill the gearbox
with grease.
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