Stihl FS 40 User manual

{
STIHL FS 40, 50 Instruction Manual
Notice d’emploi

GInstruction Manual
1 - 34
FNotice d’emploi
35 - 72

Original Instruction ManualPrinted on chlorine-free paper
Printing inks contain vegetable oils, paper can be recycled.
© ANDREAS STIHL AG & Co. KG, 2016 0458-546-8221-D. VA1.F16. 0000001091_016_GB
FS 40, FS 40 C, FS 50, FS 50 C
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
Guide to Using this Manual 2
Safety Precautions and Working
Techniques 2
Approved Combinations of Cutting
Attachment, Deflector, Handle and
Harness 9
Mounting the Loop Handle 10
Mounting the Deflector 10
Mounting the Cutting Attachment 11
Fuel 14
Fueling 15
Starting / Stopping the Engine 17
Operating Instructions 19
Cleaning the Air Filter 19
Engine Management 20
Adjusting the Carburetor 20
Spark Plug 21
Engine Running Behavior 22
Storing the Machine 22
Maintaining the Mowing Head 22
Inspections and Maintenance by
Dealer 26
Maintenance and Care 27
Main Parts 29
Specifications 30
Maintenance and Repairs 31
Disposal 32
STIHL Limited Emission Control
Warranty Statement 32

FS 40, FS 40 C, FS 50, FS 50 C
English
2
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.
Pictograms
All the pictograms attached to the
machine are shown and explained in this
manual.
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.
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.
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
Safety Precautions and
Working Techniques
Some special safety pre-
cautions have to be
observed when working
with this power tool
because of the very high
speed of the cutting
attachment.
It is important that you
read the instruction man-
ual before first use and
keep it in a safe place for
future reference. Non-
observance of the
instruction manual may
result in serious or even
fatal injury.

FS 40, FS 40 C, FS 50, FS 50 C
English
3
Do not lend or rent your power tool
without the instruction manual. Be sure
than anyone using your power tool
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. 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.
Depending on the cutting attachment
fitted, use your trimmer only for cutting
grass, wild growth 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 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
cutting attachments and accessories in
order to avoid the risk of accidents and
damage to the machine.
STIHL recommends the use of genuine
STIHL cutting attachments and
accessories. They are specifically
designed to match the product and meet
your performance requirements.
The deflector on this power tool cannot
protect the operator from all objects
thrown by the cutting attachment
(stones, glass, wire, etc.). Such objects
may ricochet and then hit the operator.
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.).
WARNING
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.
STIHL offers a comprehensive range of
personal protective clothing and
equipment.
Transporting the Power Tool
Always turn off the engine.
Carry the unit properly balanced by the
drive tube or loop handle.
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 sturdy shoes with
non-slip soles.
To reduce the risk of eye
injuries, wear snug-fitting
safety glasses in accord-
ance with European
Standard EN 166. Make
sure the safety glasses
are a good fit.
Wear robust work gloves
made of durable material
(e.g. leather).
546BA001 KN

FS 40, FS 40 C, FS 50, FS 50 C
English
4
In vehicles: 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.
–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. To reduce the risk of
injury, never use metal cutting
attachments.
–The stop switch must move easily to
0.
–Check smooth action of choke
knob, throttle trigger lockout and
throttle trigger – the throttle trigger
must return automatically to the idle
position. The choke lever must
spring back from the g and <
positions to the run position F when
the throttle trigger lockout and
throttle trigger are squeezed.
–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 attachment for
correct and secure assembly and
good condition.
–Check protective devices (e.g.
deflector for cutting attachment) for
damage or wear. Always replace
damaged parts. Never operate the
unit with a damaged deflector.
–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.
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 power tool as you would in an
emergency. To avoid damage, do not
throw the machine to the ground when
practicing.
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 cutting attachment must
be clear of the ground and all other
obstructions because it may begin to run
when the engine starts.
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.
After fueling, insert the
fuel cap with hinged grip
(bayonet-type cap) cor-
rectly in the opening, turn
it clockwise as far as stop
and fold the grip down.

FS 40, FS 40 C, FS 50, FS 50 C
English
5
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.
Do not drop start the power tool – start
the engine as described in the
instruction manual.
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 combustible materials (e.g.
wood chips, bark, dry grass, fuel).
Holding and Controlling the Unit
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 – move the stop switch in
the direction of 0.
The cutting attachment may catch and
fling objects a great distance and cause
injury - therefore, 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 maintain this
distance from other objects (vehicles,
windows). Even maintaining a distance
of 15 meters or more cannot exclude the
potential danger.
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
regularly. If the cutting attachment
continues to rotate when the engine is
idling, have the machine checked by
your servicing dealer. STIHL
recommends a STIHL servicing dealer.
Take special care in slippery conditions
(ice, wet ground, snow), on slopes or
uneven ground.
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.
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.
To reduce the risk of
injury, avoid contact with
the cutting attachment.
Note that the cutting
attachment continues to
run for a short period
after you let go of the
throttle trigger – flywheel
effect.
546BA002 KN
15m (50ft)

FS 40, FS 40 C, FS 50, FS 50 C
English
6
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.
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
unit checked by your servicing dealer.
Do not operate your power tool with the
choke lever in the warm start position <
– the engine speed cannot be controlled
in this position.
Special care must be taken when
working in difficult, over-grown terrain.
When cutting high scrub, under bushes
and hedges: Keep cutting attachment at
a minimum height of 15 cm to avoid
harming small animals.
Always shut off the engine before
leaving the unit 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.
–Replace damaged 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.
Do not continue using or attempt to
repair damaged or cracked cutting
attachments by welding, straightening or
modifying the shape (out of balance).
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.
When using mowing heads
Use only the deflector with properly
mounted line limiting blade to ensure the
mowing lines are automatically trimmed
to the approved length.
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.
To reduce the risk
of injury from
thrown objects,
never operate the
power tool without
the proper deflec-
tor 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 per-
sonal injury or damage
the cutting attachment
and property (e.g. parked
vehicles, windows).

FS 40, FS 40 C, FS 50, FS 50 C
English
7
To reduce the risk of injury, always turn
off the engine before adjusting the nylon
line of manually 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
components (e.g. clutch, polymer
housing components) – and this can
increase the risk of injury from the
cutting attachment rotating while the
engine is idling.
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 genuine
STIHL replacement parts. These parts
are specifically designed to match your
machine model and meet your
performance requirements.
To reduce the risk of injury from
unintentional engine startup, always
shut off the engine and disconnect the
spark plug boot before performing any
repairs, maintenance or cleaning work. –
Exception: Carburetor and idle speed
adjustments.
Do not turn the engine over on the
starter with the spark plug boot or spark
plug removed 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.
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.

FS 40, FS 40 C, FS 50, FS 50 C
English
8
Symbols on Deflectors
An arrow on the deflector (inside and
outside) shows the correct direction of
rotation of the cutting attachments.
Mowing Head with Nylon Lines
Nylon line achieves a soft cut for edging
and trimming around fence posts, trees,
etc. – less risk of damaging tree bark.
WARNING
To reduce the risk of injury, never use
steel wire in place of the nylon cutting
line.
STIHL PolyCut 6-3 Mowing Head with
Polymer Blades
For mowing unobstructed edges of
meadows (without posts, fences, trees
or similar obstacles).
It is important to follow the maintenance
instructions for the Polycut mowing
head.
Check the wear limit marks!
Wear limit marks are integrated in the
base of the PolyCut.
Do not continue using the PolyCut 6-3 if
one of the circular holes (1; arrow)
becomes visible or if the projecting rim
(2; arrow) has worn away. Install a new
mowing head.
WARNING
If the wear limit marks are ignored, there
is a risk of the cutting tool shattering and
flying parts injuring the operator or
bystanders.
To reduce the risk of accidents from
shattered blades, avoid contact with
stones, metal and similar solid objects.
Check PolyCut blades for cracks at
regular intervals. If a crack is found in
one of the blades, always replace all the
blades.
000BA019 KN
1
002BA073 KN
2
002BA074 KN

FS 40, FS 40 C, FS 50, FS 50 C
English
9
Approved Combinations
Select correct combination from the
table according to the cutting
attachment you intend to use.
WARNING
For safety reasons no other
combinations are permitted – risk of
accidents.
Cutting Attachments
Mowing heads
1STIHL AutoCut C 5-2
2STIHL AutoCut 5-2
3STIHL DuroCut 5-2
4STIHL PolyCut 6-3
Deflector
5Deflector with blade, for mowing
heads
Handle
6Loop handle
Shoulder strap
7Shoulder strap may be used
Approved Combinations of Cutting Attachment, Deflector, Handle and Harness
Cutting Attachment Deflector Handle Shoulder Strap
0000-GXX-0401-A0
12
67
5
Schnur/LINE 2
Schnur/LINE 1
34

FS 40, FS 40 C, FS 50, FS 50 C
English
10
Your new power tool comes with the
loop handle mounted on the drive tube,
but it must be turned and lined up to suit
your requirements.
Adjusting the loop handle
Versions with screw (FS 40)
NUse a screwdriver or the
combination wrench to loosen the
screw (1) on the handle.
Versions with star knob (FS 50)
NLoosen the star knob (2) on the
handle.
All versions
NTurn the handle to the vertical
position.
The loop handle can be adjusted to suit
the height and reach of the operator and
the application by changing
distance (A).
Recommended distance (A):
about 15 cm
NSlide the handle to the required
position.
NTighten down the screw or star knob
so that the handle cannot be rotated
on the drive tube.
NPush the deflector (1) over the
clamp (2) as far as stop.
NInsert the nut (3) in the hex recess in
the deflector – make sure the holes
line up.
NInsert the screw (4) with washer and
tighten it down firmly.
Mounting the Loop Handle
2
1
546BA003 KN
545BA004 KN
546BA004 KN
A
Mounting the Deflector
1
2
232BA066 KN
4
546BA005 KN
3

FS 40, FS 40 C, FS 50, FS 50 C
English
11
Placing power tool on the ground
NSwitch off the engine.
NLay your trimmer on its back with
the loop handle and shroud pointing
down and the output shaft facing up.
Thrust Plate
The thrust plate (1) is shipped with the
DuroCut 5-2 and PolyCut 6-3. It is only
required for these mowing heads.
STIHL AutoCut 5-2 mowing head,
STIHL AutoCut C 5-2 mowing head
NPull the thrust plate (1), if fitted, off
the shaft (2).
STIHL PolyCut 5-2 mowing head,
STIHL FixCut 6-3 mowing head
NSlip the thrust plate (1) over the
shaft (2) and engage the hex
recess (3) on the external
hexagon (4).
Blocking the Shaft
NTo block the shaft, insert a suitable
tool (5) through the holes (6) in the
deflector and thrust plate – turn the
thrust plate back and forth if
necessary.
Fitting Mowing Head with Screw
Mounting
Keep the instruction leaflet for the
mowing head in a safe place.
Mounting the Cutting
Attachment
546BA016 KN
232BA033 KN
1
2
3
4
6
6
546BA017 KN
5

FS 40, FS 40 C, FS 50, FS 50 C
English
12
NScrew the mowing head
counterclockwise on to the shaft (1)
as far as stop.
NBlock the shaft.
NTighten down the mowing head
firmly.
NOTICE
Remove the tool used to block the shaft.
Removing the Mowing Head
NBlock the shaft.
NUnscrew the mowing head
clockwise.
Fitting Mowing Head without Screw
Mounting
Keep the instruction leaflet for the
mowing head in a safe place.
STIHL AutoCut 5-2
NFit the spring (1) in the mowing
head (2).
NWind the mowing line (3) on to the
spool (4).
NThread the nylon line through the
sleeves and fit the spool in the head.
The individual steps are described in the
instruction sheet supplied.
NSlip the mowing head (2) over the
shaft (5) and engage hex recess (7)
on the external hexagon (6).
NFit the cap (8) on the mowing head
– screw it clockwise on to the shaft
as far as stop and tighten it down
firmly.
1
002BA385 KN
1
232BA054 KN
23
4
3
7
5
2
232BA053 KN
6
8

FS 40, FS 40 C, FS 50, FS 50 C
English
13
STIHL AutoCut C 5-2
NSlip the mowing head (2) on to the
shaft – as AutoCut 5-2.
NTurn the spool (9) clockwise until
the two arrow heads line up –
secure the spool in this position.
NInsert the cap (8) in the spool, press
it down as far as stop and turn it
clockwise at the same time.
NTurn the cap until you feel
resistance and then tighten it down
firmly by hand.
STIHL PolyCut 6-3
NFit the thrust plate on the shaft.
NInsert the nut (10) in the mowing
head.
NScrew the mowing head (11)
clockwise on to the shaft (5) as far
as stop.
NBlock the shaft.
NTighten down the mowing head
firmly.
WARNING
If the mounting nut has become too
loose, fit a new one.
NOTICE
Remove the tool used to block the shaft.
Remove the mowing head.
STIHL AutoCut
NHold the mowing head steady.
NUnscrew the cap counterclockwise.
STIHL PolyCut
NBlock the shaft.
NUnscrew the mowing head
counterclockwise.
9
681BA018 KN
Schnur/LINE 2
Schnur/LINE 1
2
8
11
5
681BA019 KN
10

FS 40, FS 40 C, FS 50, FS 50 C
English
14
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 (R+M)/2.
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.
To ensure the maximum performance of
your STIHL engine, use a high quality 2-
cycle engine oil. To help your engine run
cleaner and reduce harmful carbon
deposits, STIHL recommends using
STIHL HP Ultra 2-cycle engine oil or ask
your dealer for an equivalent fully
synthetic 2-cycle engine oil.
To meet the requirements of EPA and
CARB we recommend to use STIHL HP
Ultra oil.
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 30 days 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)

FS 40, FS 40 C, FS 50, FS 50 C
English
15
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
filler cap is facing up.
A number of different filler caps are
installed as standard at the factory.
Cliplock filler cap (bayonet-type)
Threaded filler cap
Opening tank cap with hinged grip
NSwing the grip to the upright
position.
NRotate the cap about 1/4 turn
counterclockwise.
NRemove the cap.
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).
NFilling up with fuel
Closing tank cap with hinged grip
Grip must be vertical:
NFit the cap in the opening – the
marks on the cap and filler neck
must line up.
NPress the cap down as far as stop.
Fueling
002BA456 KN
002BA418 KN
002BA419 KN
001BA218 KN
001BA219 KN
001BA224 KN
001BA220 KN

FS 40, FS 40 C, FS 50, FS 50 C
English
16
NWhile holding the cap depressed,
turn it clockwise until it engages in
position.
NFold the grip flush with the top of the
cap.
Checking security of cap
–The lug on the grip must fully
engage the recess (arrow).
NGrip the cap – it is properly locked if
it cannot be turned or removed.
If the cap can be turned or removed
Bottom of cap is twisted in relation to
top:
NPlace the cap on the opening and
rotate it counterclockwise until it
engages the filler neck.
NContinue rotating the cap
counterclockwise (about a quarter
turn) – this causes the bottom of the
cap to be turned to the correct
position.
NTurn and lock the cap clockwise –
see sections on "Closing" and
"Checking security of cap".
Opening screw-type tank cap
NTurn the cap counterclockwise until
it can be removed from the tank
opening.
NRemove the cap.
001BA221 KN
001BA222 KN
001BA223 KN
Left: Bottom of cap twisted
Right: Bottom of cap correctly
positioned
001BA225 KN
001BA227 KN
001BA226 KN
002BA447 KN

FS 40, FS 40 C, FS 50, FS 50 C
English
17
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 (special accessory).
Closing screw-type tank 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
Version with loop handle
1Throttle trigger lockout
2Throttle trigger
3Stop switch with Run and 0= Stop
positions.
Function of stop switch and ignition
system
The stop switch is normally in the Run
position, i.e. when it is not depressed:
The ignition is switched on – the engine
is ready to start. If the stop switch is
moved to the 0 position, the ignition is
switched off. The ignition is switched on
again automatically after the engine
stops.
Starting the Engine
NPress the manual fuel pump
bulb (4) at least five times – even if
the bulb is filled with fuel.
Cold engine (cold start)
NPress in the choke lever (5) and turn
it to g at the same time.
Warm engine (warm start)
NPress in the choke lever (5) and turn
it to < at the same time.
002BA448 KN
Starting / Stopping the
Engine
546BA007 KN
1
3
2
4
547BA015 KN
5
547BA016 KN
5
547BA017 KN

FS 40, FS 40 C, FS 50, FS 50 C
English
18
Also use this setting if the engine has
been running but is still cold.
Cranking
NPlace the unit on the ground: It must
rest securely on the engine support
and the deflector. Check that the
cutting attachment is not touching
the ground or any other obstacles.
NMake sure you have a safe and
secure footing.
NHold the unit firmly on the ground
with your left hand and press down
– do not touch the throttle trigger or
lockout lever.
NOTICE
Do not stand or kneel on the drive tube.
NHold the starter grip with your right
hand.
Version without Easy2Start
NPull the starter grip slowly until you
feel it engage and then give it a brisk
strong pull.
Version with Easy2Start
NPull the starter grip steadily.
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 until the engine
runs.
As soon as the engine runs
NPress down the throttle trigger
lockout and open the throttle – the
choke lever moves to the run
position F. After a cold start, warm
up the engine by opening the
throttle several times.
WARNING
Make sure the carburetor is correctly
adjusted. The cutting attachment must
not rotate when the engine is idling.
Your machine is now ready for
operation.
Stopping the Engine
NMove the stop switch in the direction
of 0 – the engine stops – release
the stop switch – it springs back to
the run position.
Other Hints on Starting
Engine stalls in cold start position g or
under acceleration
NMove the choke lever to < and
continue cranking until the engine
runs.
547BA018 KN
547BA020 KN
547BA021 KN