Stihl FS 120 User manual

STIHL FS 120, 120 R
Instruction Manual2 - 42

Contents
1 Guide to Using this Manual.........................2
2 Safety Precautions and Working Techni‐
ques............................................................ 2
3 Approved Combinations of Cutting Attach‐
ment, Deflector, Handle and Harness.......12
4 Approved Power Tool Attachments.......... 13
5 Mounting the Bike Handle.........................13
6 Mounting the Loop Handle........................15
7 Adjusting the Throttle Cable......................16
8 Fitting the Carrying Ring........................... 17
9 Mounting the deflector.............................. 18
10 Mounting the Cutting Attachment..............19
11 Fuel........................................................... 22
12 Fueling...................................................... 23
13 Fitting the Harness....................................23
14 Balancing the Machine..............................25
15 Starting / Stopping the Engine.................. 26
16 Transporting the Unit................................ 28
17 Operating Instructions...............................30
18 Air filter......................................................31
19 Adjusting the Carburetor........................... 31
20 Spark Plug................................................ 32
21 Engine Running Behavior......................... 33
22 Lubricating the Gearbox............................33
23 Replacing the Starter Rope and Rewind
Spring........................................................33
24 Storing the Machine.................................. 35
25 Sharpening Metal Cutting Blades............. 35
26 Maintaining the Mowing Head...................36
27 Inspection and Maintenance by User........37
28 Inspections and Maintenance by Dealer...37
29 Maintenance and Care..............................38
30 Minimize Wear and Avoid Damage...........39
31 Main Parts.................................................40
32 Specifications............................................40
33 Maintenance and Repairs......................... 41
34 Disposal.................................................... 42
35 EC Declaration of Conformity................... 42
Dear Customer,
Thank you for choosing a quality engineered
STIHL product.
It has been built using modern production techni‐
ques and comprehensive quality assurance.
Every effort has been made to ensure your satis‐
faction and trouble-free use of the product.
Please contact your dealer or our sales company
if you have any queries concerning this product.
Your
Dr. Nikolas Stihl
1 Guide to Using this Manual
1.1 Pictograms
The meanings of the pictograms attached to the
machine are explained in this manual.
Depending on the model concerned, the follow‐
ing pictograms may be attached to your
machine.
Fuel tank; fuel mixture of gasoline
and engine oil
Operate manual fuel pump
1.2 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.
1.3 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 man‐
ual.
2 Safety Precautions and
Working Techniques
Some special safety precautions
must be observed to reduce the risk
of personal injury when operating this
power tool because of the very high
speed of its cutting attachment.
It is important that you read the
instruction manual before first use
and keep it in a safe place for future
reference. Non-observance of the
English
2 0458-251-0121-B
© ANDREAS STIHL AG & Co. KG 2021
0458-251-0121-B. VA0.E21.
Printed on chlorine-free paper Printing inks contain vegetable oils, paper can be recycled.
Original Instruction Manual 0000007695_007_GB

instruction manual may result in seri‐
ous or even fatal injury.
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 it is operated or attend a
special course in its operation.
Minors should never be allowed to use a power
tool.
Keep bystanders, especially children, and ani‐
mals 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.
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 aggrava‐
ted by strenuous work, check with your doctor
before operating a power tool.
Persons with pacemakers only: The ignition sys‐
tem of your power tool produces an electromag‐
netic field of a very low intensity. This field may
interfere with some pacemakers. STIHL recom‐
mends 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.
Depending on the cutting attachment fitted, use
your power tool only for cutting grass, wild
growth, shrubs, scrub, bushes, small diameter
trees and similar materials.
Do not use your power tool for any other purpose
because of the increased risk of accidents.
Only use cutting attachments and accessories
that are explicitly approved for this power tool
model by STIHL or are technically identical. 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 acci‐
dents 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 machine 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.
The deflector on this power tool cannot protect
the operator from all objects thrown by the cut‐
ting attachment (stones, glass, wire, etc.). Such
objects may ricochet and then hit the operator.
2.1 Clothing and Equipment
Wear proper protective clothing and equipment.
Clothing must be sturdy but allow
complete freedom of movement.
Wear snug-fitting clothing, an overall
and jacket combination, do not wear
a work coat.
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 long hair so
that it is above shoulder level.
Wear steel-toed safety boots with
non-slip soles.
Sturdy shoes with non-slip soles may be worn as
an alternative only when using mowing heads.
WARNING
To reduce the risk of eye injuries,
wear close-fitting safety glasses in
accordance with European Standard
EN 166. Make sure the safety
glasses are a comfortable and snug
fit.
Wear a face shield and make sure it is a good fit.
A face shield alone does not provide adequate
eye protection.
Wear hearing protection, e.g. earplugs or ear
muffs.
2 Safety Precautions and Working Techniques English
0458-251-0121-B 3

Wear a safety hard hat for thinning operations,
when working in high scrub and where there is a
danger of head injuries from falling objects.
Wear heavy-duty work gloves made
of durable material (e.g. leather).
STIHL offers a comprehensive range of personal
protective clothing and equipment.
2.2 Transporting the Power Tool
002BA079 KN
Always shut off the engine.
Carry the unit hanging from the shoulder strap or
properly balanced by the drive tube.
To reduce the risk of cut injuries, fit transport
guard on the cutting attachment, even when car‐
rying the tool for short distances – see also
"Transporting the Unit".
To reduce the risk of serious burn
injuries, avoid touching hot parts of
the machine, including the gearbox.
Transporting by vehicle: Properly secure your
power tool to prevent turnover, fuel spillage and
damage.
2.3 Fueling
Gasoline is an extremely flammable
fuel. Keep clear of naked flames. Do
not spill any fuel – do not smoke.
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 immedi‐
ately – if fuel gets on your clothing, change
immediately.
After fueling, tighten down the fuel
tank cap as securely as possible.
This reduces the risk of unit vibrations causing
the fuel cap to loosen or come off and spill quan‐
tities of fuel.
To reduce the risk of serious or fatal burn inju‐
ries, check for fuel leakage. If fuel leak is found,
do not start the engine.
2.4 Before Starting
Check that your power tool is properly assem‐
bled and in good condition – refer to appropriate
chapters in the instruction manual.
–Check the fuel system for leaks, paying spe‐
cial 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 (if fit‐
ted) 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.
–Check cutting tool or attachment for correct
and secure assembly and good condition.
–Check protective devices (e.g. deflector for
cutting attachment, rider plate) for damage or
wear. Always replace damaged parts. Do not
operate your machine with a damaged deflec‐
tor or worn rider plate (lettering and arrows no
longer legible).
English 2 Safety Precautions and Working Techniques
4 0458-251-0121-B

–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 the harness and handle(s) to suit your
height and reach. See chapters on “Fitting the
Harness” and “Balancing the Machine".
To reduce the risk of accidents, operate your
power tool only if it is in a safe condition.
If you use a shoulder strap or full harness: Prac‐
tice 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.
2.5 Starting the Engine
Start the engine at least 3 meters from the fuel‐
ing 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 cutting
attachment must be clear of the ground and all
other obstructions because it may begin to run
when the engine starts.
Your power tool is a one-person unit. To reduce
the risk of injury from thrown objects, do not
allow other persons within a radius of 15 meters
of your own position – even when starting.
To reduce the risk of injury, avoid
contact with the cutting attachment.
Do not drop start the power tool –
start the engine as described in the
instruction manual. Note that the cut‐
ting attachment continues to run for a
short period after you let go of the
throttle trigger – flywheel effect.
Check idle speed setting: The cutting attachment
must not rotate 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 combus‐
tible materials (e.g. wood chips, bark, dry grass,
fuel).
2.6 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.
2.6.1 Models with bike handle
002BA055 KN
Right handle on control handle, left hand on left
handle.
2.6.2 Models with loop handle
002BA080 KN
On models with a loop handle and barrier bar,
left hand on loop handle, right hand on control
handle, even if you are left-handed.
2.7 During Operation
Make sure you always have good balance and
secure footing.
In the event of impending danger or in an emer‐
gency, switch off the engine immediately by mov‐
ing the slide control / stop switch to STOP or 0.
15m (50ft)
The cutting attachment may catch and fling
objects a great distance and cause injury - there‐
fore, do not allow any other persons within a
radius of 15 meters of your own position. To
reduce the risk of damage to property, also main‐
tain this distance from other objects (vehicles,
windows). Even maintaining a distance of 15
meters or more cannot exclude the potential dan‐
ger.
The correct engine idle speed is important to
ensure that the cutting attachment stops rotating
when you let go of the throttle trigger.
Check and correct the idle speed setting regu‐
larly. If the cutting attachment continues to rotate
2 Safety Precautions and Working Techniques English
0458-251-0121-B 5

when the engine is idling, have the machine
checked by your servicing dealer. STIHL recom‐
mends an authorized STIHL servicing dealer.
Take special care in slippery conditions (ice, wet
ground, snow), on slopes or uneven ground.
Watch out for obstacles: Roots and tree stumps
which could cause you to trip or stumble.
Always stand on the ground while working, never
on a ladder, work platform or any other insecure
support.
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.
Your power tool produces toxic
exhaust fumes as soon as the engine
is running. These fumes may be col‐
orless and odorless and contain
unburned hydrocarbons and benzol.
Never run the engine indoors or in
poorly ventilated locations, even if
your model is equipped with a cata‐
lytic converter.
To reduce the risk of serious or fatal injury from
breathing toxic fumes, ensure proper ventilation
when working in trenches, hollows or other con‐
fined locations.
To reduce the risk of accidents, stop work imme‐
diately in the event of nausea, headache, visual
disturbances (e.g. reduced field of vision), prob‐
lems with hearing, dizziness, deterioration in abil‐
ity to concentrate. Apart from other possibilities,
these symptoms may be caused by an exces‐
sively 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.
The dusts, vapor and smoke produced during
operation may be dangerous to health. If the
work area is very dusty or smoky, wear a respira‐
tor.
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 prop‐
erly. 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 con‐
trolled in this position.
To reduce the risk of injury from
thrown objects, never operate the unit
without the proper deflector for the
type of cutting attachment being
used.
Inspect the work area: Stones, pieces
of metal or other solid objects may be
thrown more than 15 meters and
cause personal injury or damage the
cutting attachment and property (e.g.
parked vehicles, windows).
Special care must be taken when working in diffi‐
cult, over-grown terrain.
When cutting high scrub, under bushes and hed‐
ges: Keep cutting attachment at a minimum
height of 15 cm to avoid harming small animals.
Always shut off the engine before leaving the
machine unattended.
Check the cutting attachment at regular short
intervals during operation or immediately if there
is a noticeable change in cutting behavior:
–Turn off the engine. Hold the unit firmly and
wait for the cutting attachment to come to a
standstill.
–Check condition and tightness, look for cracks.
–Check sharpness.
–Replace damaged or dull cutting attachments
immediately, even if they have only superficial
cracks.
Clean grass and plant residue off the cutting
attachment mounting at regular intervals –
remove any build up of material from the cutting
attachment and deflector.
To reduce the risk of injury, shut off the engine
before replacing the cutting attachment.
The gearbox gets hot during opera‐
tion. To reduce the risk of burn injury,
do not touch the gearbox housing.
English 2 Safety Precautions and Working Techniques
6 0458-251-0121-B

2.8 When using mowing heads
Equip the deflector with the additional compo‐
nents specified in the instruction manual.
Use only the deflector with properly mounted line
limiting blade to ensure the mowing lines are
automatically trimmed to the approved length.
To reduce the risk of injury, always turn off the
engine before adjusting the nylon line of man‐
ually adjustable mowing heads.
Using the unit with over-long nylon cutting lines
reduces the engine's operating speed. The
clutch then slips continuously and this causes
overheating and damage to important compo‐
nents (e.g. clutch, polymer housing components)
– and this can increase the risk of injury from the
cutting attachment rotating while the engine is
idling.
2.9 Using metal cutting attach‐
ments
STIHL recommends the use of original STIHL
metal cutting attachments. They are specifically
designed to match your model and meet your
performance requirements.
Metal cutting attachments rotate at very high
speed. The forces that occur act on the machine,
the attachment and the material being cut.
Metal cutting attachments must be sharpened
regularly as specified.
Unevenly sharpened metal cutting attachments
cause out-of-balance which can impose
extremely high loads on the machine and
increase the risk of breakage.
Dull or improperly sharpened cutting edges can
put a higher load on the cutting attachment and
increase the risk of injury from cracked or broken
parts.
Inspect metal cutting attachments for cracks or
warping after every contact with hard objects
(e.g. stones, rocks, pieces of metal). To reduce
the risk of injury, remove burrs and other visible
build-ups of material (use a file) because they
may become detached and be thrown at high
speed during operation.
If a rotating metal cutting attachment makes con‐
tact with a rock or other solid object there is a
risk of sparking which may cause easily combus‐
tible material to catch fire under certain circum‐
stances. Dry plants and scrub are also easily
combustible, especially in hot and dry weather
conditions. If there is a risk of fire, do not use
metal cutting attachments near combustible
materials, dry plants or scrub. Always contact
your local forest authority for information on a
possible fire risk.
Do not continue using or attempt to repair dam‐
aged or cracked cutting attachments by welding,
straightening or modifying the shape (out of bal‐
ance).
This may cause parts of the cutting attachment
to come off and hit the operator or bystanders at
high speed and result in serious or fatal injuries.
To reduce the above-mentioned risks when
using a metal cutting attachment, never use a
metal cutting attachment with a diameter larger
than specified. It must not be too heavy. It must
be manufactured from materials of adequate
quality and its geometry must be correct (shape,
thickness).
To reduce the risk of injury, a metal cutting
attachment not manufactured by STIHL must not
be heavier, thicker, have a different shape or a
diameter larger than the largest metal cutting
attachment approved by STIHL for this power
tool model.
2.10 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 cir‐
culation (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.
2.11 Maintenance and Repairs
Service the machine regularly. Do not attempt
any maintenance or repair work not described in
2 Safety Precautions and Working Techniques English
0458-251-0121-B 7

the instruction manual. Have all other work per‐
formed by a servicing dealer.
STIHL recommends that you have servicing and
repair work carried out exclusively by an author‐
ized 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 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 inter‐
vals.
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 con‐
dition, 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.
2.12 Symbols on Deflectors
An arrow on the deflector shows the correct
direction of rotation of the cutting attachments.
Some of the following symbols are applied to the
outside of the deflector to indicate the approved
combination of cutting attachment and deflector.
Deflector may be used with mowing
heads.
Deflector must not be used with mow‐
ing heads.
Deflector may be used with grass cut‐
ting blades.
Deflector must not be used with grass
cutting blades.
Deflector may be used with brush kni‐
ves.
Deflector must not be used with brush
knives.
Deflector must not be used with
shredder blades.
Deflector must not be used with circu‐
lar saw blades.
2.13 Harness / Strap
The harness is included in the scope of supply or
available as a special accessory.
► Use a shoulder strap.
► With the engine running, attach the machine to
the shoulder strap.
Grass cutting blades and brush knives must
always be used in combination with a shoulder
strap.
English 2 Safety Precautions and Working Techniques
8 0458-251-0121-B

Circular saw blades must always be used in
combination with a full harness with a quick-
release system.
2.14 Mowing Head with Nylon Line
000BA015 KN
Nylon line achieves a soft cut for edging and
trimming around trees, fence posts, etc. – less
risk of damaging tree bark.
The mowing head comes with an instruction leaf‐
let. Refill the mowing head with nylon line as
described in the instruction leaflet.
WARNING
To reduce the risk of serious injury, never use
wire or metal-reinforced line in place of the nylon
line.
2.15 STIHL Polycut Mowing Head
with Polymer Blades
For mowing unobstructed edges of meadows
(without posts, fences, trees or similar obsta‐
cles).
Check the wear limit marks!
002BA049 KN
If one of the wear limit marks on the PolyCut
mowing head is worn through (arrow): Do not
continue using the mowing head. Install a new
one. There is otherwise a risk of injury from
thrown parts of the head.
It is important to follow the maintenance instruc‐
tions for the PolyCut mowing head.
The PolyCut can also be equipped with mowing
line in place of the polymer blades.
The mowing head comes with instruction leaflets.
Equip the mowing head with polymers blades or
nylon line as described in the instruction leaflets.
WARNING
Never use wire in place of the nylon mowing line
– risk of injury.
2.16 Risk of Kickout (Blade Thrust)
with Metal Cutting Attachments
WARNING
When using metal cutting attach‐
ments there is a risk of kickout when
the rotating blade comes into contact
with a solid object such as a tree
trunk, branch, tree stump, rock or
similar. The machine is thrown to the
right or to the rear – opposite to the
attachment's direction of rotation.
002BA135 KN
2 Safety Precautions and Working Techniques English
0458-251-0121-B 9

The risk of kickout is greatest when the black
area of the rotating cutting attachment comes
into contact with a solid object.
2.17 Grass Cutting Blade
000BA020 KN
Use for grass and weeds only – sweep the
brushcutter in an arc like a scythe.
WARNING
Improper use may damage the grass cutting
blade – risk of injury from thrown parts.
Resharpen the grass cutting blade according to
instructions when it has dulled noticeably.
2.18 Brush Knife
For cutting matted grass, wild growth and scrub
and thinning young stands with a stem diameter
of no more than 2 cm – do not cut thicker stems
– risk of accidents.
002BA355 KN
Use the brushcutter like a scythe (sweep it to the
right and left) at ground level when cutting grass
and thinning young stands.
002BA509 KN
To cut wild growth and scrub, lower the brush
knife down onto the growth to achieve a shred‐
ding effect – always keep the cutting attachment
below hip level during this process.
Exercise extreme caution when using this
method of cutting. The higher the cutting attach‐
ment is off the ground, the greater the risk of
injury from cuttings being thrown sideways.
Warning! Improper use of a brush knife may
cause it to crack, chip or shatter – risk of injury
from thrown parts.
To reduce the risk of injury it is essential to take
the following precautions:
–Avoid contact with stones, rocks, pieces of
metal and other solid foreign objects.
–Never cut wood or shrubs with a stem diame‐
ter of more than 2 cm – use a circular saw
blade for such work.
–Inspect the brush knife at regular short inter‐
vals for signs of damage. Do not continue
working with a damaged brush knife.
–Resharpen the brush knife regularly and
whenever it has dulled noticeably, and have it
balanced if necessary (STIHL recommends a
STIHL servicing dealer).
English 2 Safety Precautions and Working Techniques
10 0458-251-0121-B