Stihl FS 40, FS 50, FS 40 C, FS 50 C, FS 56 Instruction Manual
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STIHL FS 40, 50
Instruction Manual
Notice d’emploi
G Instruction Manual
1 - 34
F Notice d’emploi
35 - 70
Original Instruction ManualPrinted on chlorine-free paper
Printing inks contain vegetable oils, paper can be recycled.
© ANDREAS STIHL AG & Co. KG, 2009
0458-546-8221-A. M0-7.L09.PM.
0000001091_004_GB
FS 40, FS 40 C, FS 50, FS 50 C
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
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
Checking the Spark Plug 21
Engine Running Behavior 22
Rewind Starter 22
Storing the Machine 23
Replacing Nylon Line 23
Inspections and Maintenance by
Dealer 26
Maintenance and Care 27
Main Parts 29
Specifications 30
Special Accessories 31
Maintenance and Repairs 32
STIHL Limited Emission Control
Warranty Statement 32
FS 40, FS 40 C, FS 50, FS 50 C
English
2
Pictograms
All the pictograms attached to the
machine are shown and explained in this
manual.
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 application 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 power tool operation.
Minors should never be allowed to use a
power tool.
Bystanders, especially childeren, and
animals should not be allowed in the
area where a power tool is in use.
When the machine is not in use, shut it
off so that it does not endanger others.
Secure it against unauthorized use.
The power tool user is responsible for
avoiding injury to third parties or damage
to their property.
Do not lend or rent your machine without
the instruction manual. Be sure than
anyone using your machine
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
visions, 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 explicity approved
for this power tool model by STIHL or
Guide to Using this Manual
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 trimmer is a
high-speed, fast-cutting
power tool, some special
safety precautions must
be observed to reduce
the risk of personal injury.
It is important you read
and understand the
instruction manual before
using your machine for
the first time and keep it
in a safe place for future
reference. Non-observ-
ance of the safety
precautions may result in
serious or even fatal
injury.
FS 40, FS 40 C, FS 50, FS 50 C
English
3
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 genuine
STIHL replacement parts. These parts
are specifically designed to match your
machine model and meet your
performance requirements.
The deflector on this trimmer 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.).
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.
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.
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 of 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.
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
injury from thrown
objects, always wear a
face shield and safety
glasses.
Wear heavy-duty gloves.
546BA001 KN
Gasoline is an
extremely flammable
fuel. Keep clear of naked
flames. Do not spill any
fuel – do not smoke.
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
4
– 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.
– Smooth action of choke lever,
throttle trigger interlock 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 interlock 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.
– Cutting attachment Check 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 the 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 personal injury,
do not operate your machine if it is
damaged or not properly assembled.
If you use a shoulder strap or full
harness: Practise removing and putting
down the machine as you would in an
emergency. To avoid damage, do not
throw the machine to the ground when
practising.
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.
Your trimmer 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: 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 unit 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.
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 – fly-
wheel effect.
546BA002 KN
15m (50ft)
FS 40, FS 40 C, FS 50, FS 50 C
English
5
To reduce the risk of personal injury ,
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).
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
at regular intervals. If the cutting
attachment still rotates at idle speed,
have your dealer make proper
adjustments or repairs. STIHL
recommends a STIHL servicing dealer.
Take special care in slippery conditions,
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 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 for cutting.
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 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 tool at
minimum height of 15 cm to avoid
harming small animals.
Always shut off the engine before
leaving the unit unattended.
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 injuryfrom
thrown objects,
never operate the
unit without the
proper deflector for
the type of cutting
attachment being
used.
Check the work area:
Stones, pieces of metal
or other solid objects can
be thrown 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
6
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 tool
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.
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 ("white finger
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
sensation)
– Low outside temperatures
– Amount of gripping force (holding
the power tool tightly restricts
circulation)
Users who use the machine periodically
or for long periods or users who
repeatedly experience corresponding
symptoms (e.g., tingling sensation in
fingers), should undergo a medical
examination.
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.
FS 40, FS 40 C, FS 50, FS 50 C
English
7
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.
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.
STIHL FixCut
Check the wear limit marks!
N If the raised moldings (1) on the
base of the attachment are worn as
shown in the illustration (above
right), do not continue using the
mowing head. Install a new one.
There is otherwise a risk of injury
from thrown parts of the head.
000BA019 KN
To reduce the risk of injury,
never use steel wire in place of
the nylon cutting line.
FS 40, FS 40 C, FS 50, FS 50 C
English
8
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.
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.
If the wear limit marks are
ignored, there is a risk of the
cutting tool shattering and flying
parts injuring the operator or
bystanders.
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.
Only mowing heads (1, 2, 3, 4) may be
used on trimmers with a curved drive
tube and loop handle.
Cutting Attachments
Mowing heads
1 STIHL AutoCut C 5-2
2 STIHL AutoCut 5-2
3 STIHL PolyCut 6-3
4 STIHL FixCut 5-2
Deflector
5 Deflector with blade for mowing
heads only (see "Mounting the
Deflector").
Handle
6 Loop handle
Shoulder strap
7 Shoulder strap may be used
Equipment
Among other parts, the complete unit
includes:
– Cutting attachment
– Deflector
– Handle
– Shoulder strap (special accessory)
Approved Combinations of Cutting Attachment, Deflector, Handle and Harness
Cutting attachment Deflector Handle Harness/Strap
546BA012 KN
1
2
6
7
5
Schnur/LINE 2
Schnur/LINE 1
3
4
For safety reasons only the
cutting attachments, deflectors,
handles and harnesses shown in
each row of the table may be used
together. No other combinations
are permitted because of the risk
of accidents.
To reduce the risk of injury,
avoid contact with the rotating
cutting attachment.
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)
N Use a screwdriver or the
combination wrench to loosen the
screw (1) on the handle.
Versions with star knob (FS 50)
N Loosen the star knob (2) on the
handle.
All versions
N Turn 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
N Slide the handle to the required
position.
N Tighten down the screw or star knob
so that the handle cannot be rotated
on the drive tube.
N Push the deflector (1) over the
clamp (2) as far as stop.
N Insert the nut (3) in the hex recess in
the deflector – make sure the holes
line up.
N Insert 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
Preparations
N Lay your trimmer on sits back with
the loop handle and shroud pointing
down and the output shaft facing up.
Thrust Plate
The thrust plate is shipped with the
PolyCut 6-3 and FixCut 5-2. It is only
required for these mowing heads.
STIHL AutoCut 5-2 mowing head,
STIHL AutoCut C 5-2 mowing head
N Pull the thrust plate (1), if fitted, off
the shaft.
STIHL PolyCut 6-3 mowing head,
STIHL FixCut 5-2 mowing head
N Slip the thrust plate (1) over the
shaft (2) and engage hex recess (3)
on the external hexagon (4).
Mounting the Mowing Head
Keep the instruction sheet for the
mowing head in a safe place.
STIHL AutoCut 5-2
N Fit the spring (1) in the mowing
head (2).
N Wind the mowing line (3) on to the
spool (4).
N Thread the nylon line through the
sleeves and fit the spool in the head.
The individual steps are described in the
instruction sheet supplied.
Mounting the Cutting
Attachment
546BA006 KN
232BA033 KN
1
2
3
4
1
232BA054 KN
2
3
4
3
FS 40, FS 40 C, FS 50, FS 50 C
English
12
N Slip the mowing head (2) over the
shaft (5) and engage hex recess (7)
on the external hexagon (6).
N Fit the cap (8) on the mowing head
– screw it clockwise on to the shaft
as far as stop and tighten it down
firmly.
STIHL AutoCut C 5-2
N Slip the mowing head (2) on to the
shaft – as AutoCut 5-2.
N Turn the spool (9) clockwise until
the two arrow heads line up –
secure the spool in this position.
N Insert the cap (8) in the spool, press
it down as far as stop and turn it
clockwise at the same time.
N Turn the cap until you feel
resistance and then tighten it down
firmly by hand.
STIHL PolyCut 6-3
N Fit the thrust plate on the shaft.
N Insert the nut (10) in the mowing
head.
N Screw the mowing head (11)
clockwise on to the shaft (5) as far
as stop.
N Block the shaft – see "Blocking the
Shaft".
N Tighten down the mowing head.
7
5
2
232BA053 KN
6
8
9
681BA018 KN
Schnur/LINE 2
Schnur/LINE 1
2
8
Remove the locking pin.
11
5
681BA019 KN
10
FS 40, FS 40 C, FS 50, FS 50 C
English
13
Blocking the shaft
N To block the shaft, insert a suitable
tool (12) through the holes (13) in
the deflector and thrust plate – turn
the thrust plate back and forth if
necessary.
STIHL FixCut 5-2
N Slip the thrust plate (2) over the
shaft.
N Place the mowing head on the
thrust plate (2).
N Push the thrust washer (3) over the
shaft (1) so it is seated on the base.
N Block the shaft – see "Blocking the
Shaft".
N Use the combination wrench (5)
(special accessory) to screw the
mounting nut (4) on to the output
shaft clockwise and tighten it down
firmly.
Removing the mowing head
STIHL AutoCut
N Hold the mowing head steady.
N Unscrew the cap counterclockwise.
STIHL PolyCut
N Block the shaft – see "Blocking the
Shaft".
N Unscrew the mowing head
counterclockwise.
STIHL FixCut
N Block the shaft – see "Blocking the
Shaft".
N Use the combination wrench
(special accessory) to loosen and
unscrew the mounting nut
counterclockwise from the output
shaft.
Collar (see arrow) must engage
the mowing head's mounting hole.
Remove the locking pin.
3
1
2
4
232BA074 KN
5
If the mounting nut turns too
freely, fit a new one.
FS 40, FS 40 C, FS 50, FS 50 C
English
14
Adjusting Nylon Line
STIHL AutoCut
N Hold the rotating mowing head
above the ground – tap it on the
ground once – about 3 cm fresh line
is advanced.
N The blade (1) on the deflector (2)
trims surplus line to the correct
length – avoid tapping the mowing
head more than once at a time.
Line feed operates only if both lines still
have a minimum length of 2.5 cm.
If the line is shorter than 2.5 cm:
N Turn the trimmer on its back.
N Press down the cap on the spool as
far as stop.
N Pull the ends of the lines out of the
spool.
If the spool is empty, see "Replacing
Nylon Line".
All other mowing heads
Refer to the instructions supplied with
the mowing head.
Replacing Nylon Line / Polymer
Blades
STIHL AutoCut
See chapter on "Replacing Nylon Line".
STIHL PolyCut, FixCut
Refer to the instructions supplied with
the mowing head.
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.
Use only STIHL two-stroke engine oil or
equivalent high-quality two-stroke air-
cooled engine oils for mixing.
To reduce the risk of injury,
always shut off the engine before
adjusting the mowing line by
hand.
1
232BA007 KN
2
To reduce the risk of injury,
always shut off the engine before
adjusting the mowing line by
hand.
Fuel
FS 40, FS 40 C, FS 50, FS 50 C
English
15
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.
Preparations
N Before fueling, clean the filler cap
and the area around it to ensure that
no dirt falls into the tank.
N Position the machine so that the
filler cap is facing up.
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)
Fueling
547BA009 KN
FS 40, FS 40 C, FS 50, FS 50 C
English
16
Opening the Cap
N Swing the grip to the upright
position.
N Rotate the cap about 1/4 turn
counterclockwise.
N Remove 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 (special accessory).
Closing the Cap
N With the grip upright, insert the cap
in the fuel tank opening so that the
marks line up.
N Rotate the cap clockwise as far as
stop (about 1/4 turn).
N Fold the grip down so that it is flush
with the top of the cap.
If the grip does not lie completely flat on
the cap and the grip's lug does not
engage the recess (see arrow), the cap
is not properly closed. You must repeat
the above steps.
Changing the Fuel Pickup Body
Change the fuel pickup body every year:
N Open the tank cap and drain the fuel
tank.
N Use a hook to pull the fuel pickup
body out of the tank and take it off
the hose.
N Push the new pickup body into the
hose.
N Place the pickup body in the tank.
N Fill up with fuel and close the tank
cap.
547BA010 KN
547BA011 KN
547BA012 KN
547BA013 KN
Do not kink the fuel hose – do not
use any sharp or pointed tools.
547BA014 KN
FS 40, FS 40 C, FS 50, FS 50 C
English
17
Controls
Version with loop handle
1 Throttle trigger interlock
2 Throttle trigger
3 Stop switch with Run and 0 =Stop
positions.
Function of stop switch and ignition
system
The stop switch is normally in the Run
position: Ignition is on in this position –
the engine is ready to start and may be
started. If the stop switch is moved to the
0 position, the ignition is switched off. It
is automatically switched on again after
the engine comes to a standstill.
Starting the Engine
N Press the fuel pump bulb (4) at least
five times – even if the bulb is
already filled with fuel.
Cold engine (cold start)
N Press in the choke lever (5) and turn
it to g at the same time.
Warm engine (warm start)
N Press in the choke lever (5) and turn
it to < at the same time.
Also use this setting if the engine has
been running but is still cold.
Starting
N Place the unit on the ground: It must
rest securely on the engine support
and the deflector. Check that the
cutting tool is not touching the
ground of any other obstacles.
N Make sure you have a firm footing.
N Hold the unit firmly on the ground
with your left hand and press down
– do not touch the throttle trigger or
interlock lever.
Starting / Stopping the
Engine
546BA007 KN
1
3
2
4
547BA015 KN
5
547BA016 KN
5
547BA017 KN
Do not stand or kneel on the drive
tube.
547BA018 KN
FS 40, FS 40 C, FS 50, FS 50 C
English
18
N Hold the starter grip with your right
hand.
Models without ErgoStart
N Pull the starter grip slowly until you
feel it engage and then give it a brisk
strong pull.
Models with ErgoStart
N Pull the starter grip steadily.
N Do not let the starter grip snap back.
Guide it slowly back into the housing
so that the starter rope can rewind
properly.
N Continue cranking until the engine
runs.
As soon as the engine runs
N Press down the interlock lever 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.
Your machine is now ready for
operation.
Shut off the engine.
N Move 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
N Move the choke lever to < and
continue cranking until the engine
runs.
Engine does not start in warm start
position <
N Move the choke lever to g and
continue cranking until the engine
runs.
If the engine does not start
N Check that all settings are correct.
N Check that there is fuel in the tank
and refuel if necessary.
N Check that spark plug boot is
properly connected.
N Repeat the starting procedure.
Fuel tank run until dry
N After refueling, press the fuel pump
bulb at least five times – even if the
bulb is filled with fuel.
N Set the choke lever to suit the
engine temperature.
N Now start the engine.
Do not pull out the starter rope all
the way – it might otherwise
break.
547BA020 KN
Make sure the carburetor is
correctly adjusted. The cutting tool
must not rotate when the engine is
idling.
547BA021 KN
FS 40, FS 40 C, FS 50, FS 50 C
English
19
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
N Move the choke lever (1) to <.
N Turn the screw (2) in the filter
cover (3) counterclockwise until the
cover is loose.
N Ease the filter cover (3) over the
choke lever and lift it away.
N Clean away loose dirt from around
the filter.
N Reach into the recess (4) in the filter
housing and take out the felt
filter (5).
N Fit a new felt filter element (5). 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.
N Fit the felt filter (5) in the filter
housing, make sure it is properly
seated – the arrow points to the
recess.
N Move the choke lever (1) to <.
N Fit the filter cover in position,
making sure the screw is square.
Tighten down the screw.
Operating Instructions Cleaning the Air Filter
1
547BA022 KN
2
3
Replace damaged parts.
547BA023 KN
4
FS 40, FS 40 C, FS 50, FS 50 C
English
20
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
make corrections with the adjusting
screws within fine limits.
Standard Setting
N Shut odd the engine.
N Mount a cutting tool – we
recommend you use a mowing
head.
N Check the air filter and replace the
element if necessary.
N Have the spark arresting screen
(not all markets) checked – see
“Inspection and Maintenance by
Dealer"
N Turn the high speed screw (H)
counterclockwise as far as stop
(max. 3/4 turn possible).
N Turn the low speed screw (L)
counterclockwise as far as stop
(max. 3/4 turn possible).
N Start and warm up the engine if
necessary.
N Adjust idle speed with the idle speed
screw (LA) so that the cutting tools
does not turn.
Fine Tuning for Operation in
Mountains or at Sea Level
A slight correction of the setting may be
necessary if engine power is not
satisfactory when operating at high
altitude or at sea level.
N Warm up the engine.
At high altitude
N Turn high speed screw (H)
clockwise (leaner) – no further than
stop.
At sea level
N Turn high speed screw (H)
counterclockwise (richer) – no
further than stop.
Adjusting Idle Speed
N Warm up the engine.
Engine stops while idling
N Turn the idle speed screw (LA)
slowly clockwise until the engine
runs smoothly – the cutting
attachment must not turn.
Engine Management Adjusting the Carburetor
547BA024 KN
FS 40, FS 40 C, FS 50, FS 50 C
English
21
Cutting attachment rotates when
engine is idling
N Turn the idle speed screw (LA)
counterclockwise until the tool stops
moving and then turn the screw
another full 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
N Turn the low speed screw (L)
counterclockwise, no further than
stop, until the engine runs and
accelerates smoothly.
Erratic idling behavior, engine speed
drops when swinging the machine
Idle setting is too rich
N Turn the low speed screw (L)
clockwise (1/8 of a turn or 45° at a
time) until the engine runs smoothly
and accelerates well.
It is usually necessary to change the
setting of the idle speed screw (LA) after
corrections to the low speed screw (L).
If the engine is down on power, difficult
to start or runs poorly at idle speed, first
check the spark plug.
Removing the Spark Plug
N Shut down the engine.
The spark plug boot (2) is located in the
cap (1).
N Pull off the spark plug boot (2)
together with the cap (1).
N Unscrew the spark plug (3).
If the cap becomes detached when you
pull off the spark plug boot, see
"Installing the Spark Plug."
Checking the Spark Plug
Wrong fuel mix (too much engine oil in
the gasoline), a dirty air filter and
unfavorable running conditions (mostly
at part throttle etc.) affect the condition
of the spark plug. These factors cause
deposits to form on the insulator nose
which may result in trouble in operation.
N Clean dirty spark plug.
N Check the electrode gap (A) and
readjust if necessary – see
"Specifications."
N Use only resistor type spark plugs of
the approved range.
Rectify problems which have caused
fouling of spark plug:
N Too much oil in fuel mix.
N Dirty air filter.
N Unfavorable running conditions,
e.g. operating at part load.
If the cutting tool continues to
rotate when the engine is idling,
have your machine checked and
repaired by your servicing dealer.
Checking the Spark Plug
The cap (1) protects the spark
plug from damage. Do not operate
the power tool without the cap –
replace a damaged cap.
547BA025 KN
1
000BA002 KN
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