STIHL FS 50, FS 40 Owner's Manual
STIHL FS 40, 50
Warning!
Read and follow all safety
precautions in Instruction Manual –
improper use can cause serious or
fatal injury.
Advertencia!
Lea y siga todas las precauciones
de seguridad dadas en el manual
de instrucciones – el uso incorrecto
puede causar lesiones graves o
mortales.
{
Instruction Manual
Manual de instrucciones
Instruction Manual
1 - 44
Manual de instrucciones
45 - 93
Contents
English
Guide to Using this Manual 2
Safety Precautions and Working
Techniques 3
Approved Combinations of Cutting
Attachment, Deflector, Handle and
Harness 15
Mounting the Loop Handle 16
Mounting the Deflector 16
Mounting the Cutting Attachment 17
Original Instruction ManualPrinted on chlorine-free paper
Fuel 20
Fueling 21
Starting / Stopping the Engine 24
Operating Instructions 26
Cleaning the Air Filter 26
Engine Management 27
Adjusting the Carburetor 27
Spark Plug 28
Engine Running Behavior 29
Rewind Starter 30
Storing the Machine 30
Replacing Nylon Line 30
Inspections and Maintenance by
Printing inks contain vegetable oils, paper can be recycled.
Dealer 33
Maintenance and Care 34
Main Parts 36
Specifications 37
Special Accessories 38
Maintenance and Repairs 39
STIHL Incorporated Federal
Emission Control Warranty
Statement 39
STIHL Incorporated California
Exhaust and Evaporative
Emissions Control Warranty
Statement 41
Trademarks 43
Allow only persons who fully understand
this manual to operate your trimmer.
To receive maximum performance and
satisfaction from your STIHL trimmer, it
is important that you read, understand
and follow the safety precautions and
the operating and maintenance
instructions in chapter "Safety
Precautions and Working Techniques"
before using your trimmer. For further
information you can go to
www.stihlusa.com.
Contact your STIHL dealer or the STIHL
distributor for your area if you do not
understand any of the instructions in this
manual.
Warning!
Because a trimmer is a high-speed cutting tool some special safety
precautions must be observed to reduce
the risk of personal injury. Careless or
improper use may cause serious or
even fatal injury.
Make sure your unit is equipped with the
proper deflector, handle and harness for
the type of cutting attachment being
used. Always wear proper eye
protection.
{
© ANDREAS STIHL AG & Co. KG, 2011
0458-546-8621-C. M13-5.H11.CP.
0000001050_008_GB
FS 40, FS 40 C, FS 50, FS 50 C
1
English
Guide to Using this Manual
Pictograms
The meanings of the pictograms
attached to or embossed on the
machine are explained in this manual.
Depending on the model concerned, the
following pictograms may be on your
machine.
Fuel tank for gasoline
and engine oil mixture
Press to operate decompression valve
Manual fuel pump
Press to operate manual
fuel pump
Symbols in Text
Many operating and safety instructions
are supported by illustrations.
The individual steps or procedures
described in the manual may be marked
in different ways:
N A bullet marks a step or procedure.
A description of a step or procedure that
refers directly to an illustration may
contain item numbers that appear in the
illustration. Example:
N Loosen the screw (1).
N Lever (2) ...
In addition to the operating instructions,
this manual may contain paragraphs
that require your special attention. Such
paragraphs are marked with the
symbols and signal words described
below:
Danger!
Indicates an imminent risk of severe or
fatal injury.
Engineering Improvements
STIHL’s philosophy is to continually
improve all of its products. As a result,
engineering changes and improvements
are made from time to time. Therefore,
some changes, modifications and
improvements may not be covered in
this manual. If the operating
characteristics or the appearance of
your machine differs from those
described in this manual, please contact
your STIHL dealer for assistance.
Filler hole for gear
lubricant
Air intake summer mode
Air intake winter mode
Handle heating
2
Warning!
Indicates a hazardous situation which, if
not avoided, could result in severe or
fatal injury.
Caution!
Indicates a risk of property damage,
including damage to the machine or its
individual components.
FS 40, FS 40 C, FS 50, FS 50 C
English
Safety Precautions and
Working Techniques
Because a trimmer is a
high-speed, fast-cutting
power tool, special safety
precautions must be
observed to reduce the
risk of personal injury.
It is important that you
read, fully understand
and observe the following
safety precautions and
warnings. Read the
instruction manual and
the safety precautions
periodically. Careless or
improper use may cause
serious or fatal injury.
The terminology utilized in this manual
when referring to the power tool reflects
the type of cutting attachments that may
be mounted on it. The term "trimmer" is
used to designate an FS unit that is
equipped with a nylon line head or a
head with flexible plastic blades (i.e., the
PolyCut head).
Warning!
As more fully explained later in these
Safety Precautions, to reduce the risk of
personal injury, make sure your unit is
equipped with the proper handle, harness and deflector for the type of cutting
attachment you are using. Use only cutting attachments that are specifically
authorized by STIHL for use on your FS
model. To reduce the risk of severe or
fatal injury from blade contact and / or
loss of control, never attempt to use a
metal blade on this trimmer.
Have your STIHL dealer show you how
to operate your power tool. Observe all
applicable local safety regulations,
standards and ordinances.
Warning!
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.
Warning!
The use of this machine may be hazardous. If the rotating line or blade comes in
contact with your body, it will cut you.
When it comes in contact with solid foreign objects such as rocks or bits of
metal, it may fling them directly or by ricochet in the direction of bystanders or
the operator. Striking such objects could
damage the cutting attachment. Thrown
objects, including broken heads or
blades, may result in serious or fatal
injury to the operator or bystanders.
Use your trimmer equipped with the
appropriate cutting attachment only for
cutting grass and similar material.
Warning!
Do not use it for other purposes, since
misuse may result in personal injury or
property damage, including damage to
the machine.
Warning!
Minors should never be allowed to use
this power tool. Bystanders, especially
children, and animals should not be
allowed in the area where it is in use.
Warning!
To reduce the risk of injury to bystanders and damage to property, never let
your power tool run unattended. When it
is not in use (e.g. during a work break),
shut it off and make sure that unauthorized persons do not use it.
Most of these safety precautions and
warnings apply to the use of all STIHL
trimmers. Different models may have
different parts and controls. See the
appropriate section of your instruction
manual for a description of the controls
and the function of the parts of your
model.
Safe use of a trimmer involves
1. the operator
2. the power tool
3. the use of the power tool.
THE OPERATOR
Physical Condition
You must be in good physical condition
and mental health and not under the
influence of any substance (drugs,
alcohol, etc.) which might impair vision,
dexterity or judgment. Do not operate
this machine when you are fatigued.
FS 40, FS 40 C, FS 50, FS 50 C
3
English
Warning!
Be alert – if you get tired, take a break.
Tiredness may result in loss of control.
Working with any power tool can be
strenuous. If you have any condition
that might be aggravated by strenuous
work, check with your doctor before
operating this machine.
Warning!
Prolonged use of a power tool (or other
machines) exposing the operator to
vibrations may produce whitefinger disease (Raynaud's phenomenon) or
carpal tunnel syndrome.
These conditions reduce the hand's
ability to feel and regulate temperature,
produce numbness and burning
sensations and may cause nerve and
circulation damage and tissue necrosis.
All factors which contribute to
whitefinger disease are not known, but
cold weather, smoking and diseases or
physical conditions that affect blood
vessels and blood transport, as well as
high vibration levels and long periods of
exposure to vibration are mentioned as
factors in the development of whitefinger
disease. In order to reduce the risk of
whitefinger disease and carpal tunnel
syndrome, please note the following:
– Most STIHL power tools are
available with an anti-vibration
("AV") system designed to reduce
the transmission of vibrations
created by the machine to the
operator's hands. An AV system is
recommended for those persons
using power tools on a regular or
sustained basis.
– Wear gloves and keep your hands
warm.
– Keep the AV system well
maintained. A power tool with loose
components or with damaged or
worn AV buffers will tend to have
higher vibration levels.
– Maintain a firm grip at all times, but
do not squeeze the handles with
constant, excessive pressure. Take
frequent breaks.
All the above-mentioned precautions do
not guarantee that you will not sustain
whitefinger disease or carpal tunnel
syndrome. Therefore, continual and
regular users should closely monitor the
condition of their hands and fingers. If
any of the above symptoms appear,
seek medical advice immediately.
Warning!
The ignition system of the STIHL unit
produces an electromagnetic field of a
very low intensity. This field may interfere with some pacemakers. To reduce
the risk of serious or fatal injury, persons
with a pacemaker should consult their
physician and the pacemaker manufacturer before operating this tool.
Proper Clothing
Warning!
To reduce the risk of injury, the operator
should wear proper protective apparel.
Warning!
The deflector provided with your power
tool will not protect the operator from all
foreign objects (gravel, glass, wire, etc.)
thrown back by the rotating cutting
attachment. Thrown objects may also
ricochet and strike the operator.
Warning!
To reduce the risk of
injury to your eyes never
operate your power tool
unless wearing goggles
or properly fitted protec-
tive glasses with
adequate top and side protection complying with ANSI Z 87.1 (or your
applicable national standard). To
reduce the risk of injury to your face
STIHL recommends that you also wear
a face shield or face screen over your
goggles or protective glasses.
4
FS 40, FS 40 C, FS 50, FS 50 C
Warning!
Power tool noise may
damage your hearing.
Wear sound barriers (ear
plugs or ear mufflers) to
protect your hearing.
Continual and regular
users should have their hearing
checked regularly.
Be particularly alert and cautious when
wearing hearing protection because
your ability to hear warnings (shouts,
alarms, etc.) is restricted.
Always wear gloves
when handling the
machine, blade and the
cutting attachment.
Heavy-duty, nonslip
gloves improve your grip
and help to protect your
hands.
Clothing must be sturdy
and snug-fitting, but allow
complete freedom of
movement. Wear long
pants made of heavy
material to help protect
your legs. Do not wear
shorts, sandals or go
barefoot.
Avoid loose-fitting jackets, scarfs,
neckties, jewelry, flared or cuffed pants,
unconfined long hair or anything that
could become caught on branches,
brush or the moving parts of the unit.
Secure hair so it is above shoulder level.
Good footing is very
important. Wear sturdy
boots with nonslip soles.
Steel-toed safety boots
are recommended.
THE POWER TOOL
For illustrations and definitions of the
power tool parts see the chapter on
"Main Parts."
Warning!
Never modify this power tool in any way.
Only attachments supplied by STIHL
and expressly approved by STIHL for
use with the specific STIHL model are
authorized. Although certain unauthorized attachments are useable with
STIHL power tools, their use may, in
fact, be extremely dangerous. For the
cutting attachments authorized by
STIHL for your unit, see the chapter
"Approved Combinations of Cutting
Attachment, Deflector, Handle and Harness" in the instruction manual or the
STIHL "Cutting Attachments, Parts &
Accessories" catalog.
English
Warning!
Never modify this power tool in any way.
Only attachments supplied by STIHL
and expressly approved by STIHL for
use with the specific STIHL model are
authorized. Although certain unauthorized attachments are useable with
STIHL power tools, their use may, in
fact, be extremely dangerous. For the
cutting attachments authorized by
STIHL for your unit, see the chapter
"Approved Combinations of Cutting
Attachment, Deflector, Handle and Harness" in the instruction manual or the
STIHL "Cutting Attachments, Parts &
Accessories" catalog.
If this 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. Check in particular that
the fuel system is tight (no leaks) and
that the controls and safety devices are
working properly. Do not continue
operating this machine if it is damaged.
In case of doubt, have it checked by your
STIHL servicing dealer.
THE USE OF THE POWER TOOL
Transporting the Power Tool
Warning!
To reduce the risk of injury from loss of
control and blade or line contact, never
carry or transport your power tool with
the cutting attachment moving.
FS 40, FS 40 C, FS 50, FS 50 C
5
English
389BA019 KN
001BA220 KN
It may be carried only in a horizontal
position. Grip the shaft in a manner that
the machine is balanced horizontally.
Keep the hot muffler away from your
body and the cutting attachment behind
you.
Warning!
Always shut off the engine and make
sure the cutting attachment has stopped
before putting a trimmer down. When
transporting it in a vehicle, properly
secure it to prevent turnover, fuel spillage and damage to the unit.
Fuel
Your STIHL power tool uses an oil-
gasoline mixture for fuel (see the
chapter on "Fuel" of your instruction
manual).
Warning!
Gasoline is an extremely
flammable fuel. If spilled
and ignited by a spark or
other ignition source, it
can cause fire and seri-
ous burn injury or
property damage. Use extreme caution
when handling gasoline or fuel mix. Do
not smoke or bring any fire or flame near
the fuel or the power tool. Note that
combustible fuel vapor may escape
from the fuel system.
Fueling Instructions
Warning!
To reduce the risk of serious injury from
burns, never attempt to refuel the unit
until it has been completely removed
from the operator.
Warning!
Fuel your power tool in well-ventilated
areas, outdoors. Always shut off the
engine and allow it to cool before refueling. Gasoline vapor pressure may
build up inside the fuel tank depending
on the fuel used, the weather conditions
and the tank venting system.
In order to reduce the risk of burns and
other personal injury from escaping gas
vapor and fumes, remove the fuel filler
cap on your power tool carefully so as to
allow any pressure build-up in the tank
to release slowly. Never remove the fuel
filler cap while the engine is running.
Select bare ground for fueling and move
at least 10 feet (3 m) from the fueling
spot before starting the engine. Wipe off
any spilled fuel before starting your
machine.
Warning!
Check for fuel leakage
while refueling and during operation. If fuel
leakage is found, do not
start or run the engine
until the leak is fixed and
any spilled fuel has been wiped away.
Take care not to get fuel on your clothing. If this happens, change your
clothing immediately.
Different models may be equipped with
different fuel caps.
Warning!
In order to reduce the risk of fuel spillage and fire from an improperly
tightened fuel cap, correctly position
and tighten the fuel cap in the fuel tank
opening.
Toolless cap with grip
To do this with this STIHL cap, raise the
grip on the top of the cap until it is upright
at a 90° angle. Insert the cap in the fuel
tank opening with the raised positioning
6
FS 40, FS 40 C, FS 50, FS 50 C
English
001BA227 KN
001BA226 KN
marks on the grip of the cap and on the
fuel tank opening lining up. Using the
grip, press the cap down firmly while
turning it clockwise as far as it will go
(approx. 1/4 turn).
Fold the grip flush with
the top of the cap. Check
the cap for tightness. If
the grip does not lie completely flush with the cap
and the detent on the grip
does not fit in the corresponding recess in the
filler opening, or if the cap
is loose in the filler opening, the cap is not
properly seated and tightened and you must
repeat the above steps.
Misaligned, damaged or broken cap
N If the cap does not drop fully into the
opening when the positioning marks
line up and/or if the cap does not
tighten properly when twisted, the
base of the cap may be prematurely
rotated (in relation to the top) to the
closed position. Such misalignment
can result from handling, cleaning
or an improper attempt at
tightening.
Left: Base of cap in closed posi-
tion (with open space)
Right: Base of cap correctly posi-
tioned for installation
N To return the cap to the open
position for installation, turn the cap
(with the grip up) until it drops fully
into the tank opening. Next, twist the
cap counterclockwise as far as it will
go (approx. 1/4 turn) – this will twist
the base of the cap into the correct
position. Then, twist the cap
clockwise, closing it normally.
N If your cap still does not tighten
properly, it may be damaged or
broken; immediately stop use of the
unit and take it to your authorized
STIHL dealer for repair.
Screw Cap
Warning!
Unit vibrations can cause
an improperly tightened
fuel filler cap to loosen or
come off and spill quantities of fuel. In order to
reduce the risk of fuel
spillage and fire, tighten the fuel filler
cap by hand as securely as possible.
See also the "Fueling" chapter in your
Instruction Manual for additional
information.
Before Starting
Warning!
Always check your power tool for proper
condition and operation before starting,
particularly the throttle trigger, throttle
trigger lockout, momentary stop switch,
cutting attachment, deflector and harness. The throttle trigger must move
freely and always spring back to the idle
position. Never attempt to modify the
controls or safety devices. Never use a
power tool that is damaged or not properly maintained.
Warning!
Do not attach any cutting attachment to
a unit without proper installation of all
required parts. Failure to use the proper
parts may cause the blade or head to fly
off and seriously injure the operator or
bystanders.
FS 40, FS 40 C, FS 50, FS 50 C
7
English
Warning!
The cutting attachment must be properly tightened and in safe operating
condition. Inspect for loose parts (nuts,
screws, etc.) Replace damaged heads
before using the power tool.
Keep the handles clean and dry at all
times; it is particularly important to keep
them free of moisture, pitch, oil, fuel mix,
grease or resin in order for you to
maintain a firm grip and properly control
your power tool.
Warning!
Check that the spark plug boot is
securely mounted on the spark plug – a
loose boot may cause arcing that could
ignite combustible fumes and cause a
fire.
Warning!
To reduce the risk
of personal injury
to the operator
from blade or line
contact and
thrown objects, make sure your unit is
equipped with the proper deflector, handle and harness for the type of cutting
attachment being used (see chart in the
chapter on "Approved Combinations of
Cutting Attachment, Deflector, Handle
and Harness")
Keep the deflector (and the attached
skirt where appropriate) adjusted
properly at all times (see chapters on
"Mounting the Deflector" and "Mounting
the Cutting Attachment" of your
instruction manual).
Arrows on the deflector (as seen from
the underside) show the correct
direction of rotation of the cutting
attachment. When viewed from above,
however, the cutting attachment rotates
clockwise.
Adjust the hand grip and harness (if you
are wearing one) to suit your size before
starting work. The machine should be
properly balanced as specified in your
instruction manual for proper control and
less fatigue in operation. To be better
prepared in case of an emergency,
practise releasing the unit from the
harness as quickly as possible.
Starting
Start the engine at least 10 feet (3 m)
from the fueling spot, outdoors only.
For specific starting instructions, see the
appropriate section of your manual.
Place the power tool on firm ground or
other solid surface in an open area.
Maintain good balance and secure
footing.
Warning!
To reduce the risk of injury from blade or
line contact, be absolutely sure that the
cutting attachment is clear of you and all
other obstructions and objects, including the ground, because when the
engine starts at starting-throttle, engine
speed will be fast enough for the clutch
to engage and move the cutting
attachment.
Once the engine has started,
immediately blip the throttle trigger,
which should release the starting throttle
and allow the engine to slow down to
idle.
With the engine running only at idle,
attach the power tool to the spring hook
of your harness (see appropriate
chapter of this manual).
Warning!
Your power tool is a one-person
machine. Do not allow other persons in
the general work area, even when
starting.
Warning!
To reduce the risk of injury from loss of
control, do not attempt to "drop start"
your power tool.
8
FS 40, FS 40 C, FS 50, FS 50 C
Warning!
002BA054 KN
When you pull the starter grip, do not
wrap the starter rope around your hand.
Do not let the grip snap back, but guide
the starter rope to rewind it properly.
Failure to follow this procedure may
result in injury to your hand or fingers
and may damage the starter
mechanism.
Important Adjustments
Warning!
To reduce the risk of personal injury
from loss of control or contact with the
running cutting attachment, do not use
your unit with incorrect idle adjustment.
At correct idle speed, the cutting attachment should not move. For directions on
how to adjust idle speed, see the appropriate section of your instruction
manual.
If you cannot set the correct idle speed,
have your STIHL dealer check your
power tool and make proper
adjustments and repairs.
Warning!
This unit is equipped with an ignition
system that is normally in operational
readiness. After the setting lever is used
to stop the engine, it automatically
springs back to the "on" position. If the
engine is warm, it may be possible to
start it by simply pulling the starter rope,
with no further adjustments. To reduce
the risk of injury, be particularly alert to
keep children away from the unit.
During Operation
Holding and Controlling the Power Tool
Always hold the unit firmly with both
hands on the handles while you are
working. Wrap your fingers and thumbs
around the handles, keeping the
handles cradled between your thumb
and forefinger. Keep your hands in this
position to have your power tool under
control at all times. Make sure your
trimmer handles and grips are in good
condition and free of moisture, pitch, oil,
fuel mix or grease.
Warning!
To reduce the risk of injury from loss of
control, never work on a ladder or on
any other insecure support. Never hold
the cutting attachment above waist
height.
English
Warning!
Never attempt to operate
your power tool with one
hand. Loss of control of
the power tool resulting
in serious or fatal injury
may result. To reduce
the risk of cut injuries, keep hands and
feet away from the cutting attachment.
Never touch a moving cutting attachment with your hand or any other part of
your body.
Warning!
Do not overreach. Keep proper footing
and balance at all times. Special care
must be taken in slippery conditions
(wet ground, snow) and in difficult, overgrown terrain. Watch for hidden
obstacles such as tree stumps, roots
and ditches to avoid stumbling. For better footing, clear away scrub and
cuttings. Be extremely cautious when
working on slopes or uneven ground.
Working Conditions
Operate and start your power tool only
outdoors in a well ventilated area.
Operate it under good visibility and
daylight conditions only. Work carefully.
FS 40, FS 40 C, FS 50, FS 50 C
9
English
15m (50ft)
Warning!
As soon as the engine is
running, this product
generates toxic exhaust
fumes containing chemicals, such as unburned
hydrocarbons (including
benzene) and carbon monoxide, that
are known to cause respiratory problems, cancer, birth defects, or other
reproductive harm. Some of the gases
(e.g. carbon monoxide) may be colorless and odorless. To reduce the risk of
serious or fatal injury/illness from inhaling toxic fumes, never run the machine
indoors or in poorly ventilated locations.
Warning!
If the vegetation being cut or the surrounding ground is coated with a
chemical substance (such as an active
pesticide or herbicide), read and follow
the instructions and warnings that
accompanied the substance at issue.
Warning!
Inhalation of certain dusts, especially
organic dusts such as mold or pollen,
can cause susceptible persons to have
an allergic or asthmatic reaction. Substantial or repeated inhalation of dust
and other airborne contaminants, in particular those with a smaller particle size,
may cause respiratory or other illnesses. Control dust at the source
where possible. Use good work practices, such as operating the unit so that
the wind or operating process directs
any dust raised by the power tool away
from the operator. Follow the recommendations of EPA/OSHA/NIOSH and
occupational and trade associations
with respect to dust ("particulate matter"). When the inhalation of dust cannot
be substantially controlled, i.e., kept at
or near the ambient (background) level,
the operator and any bystanders should
wear a respirator approved by
NIOSH/MSHA for the type of dust
encountered.
Operating Instructions
Warning!
Do not operate your power tool using
the starting throttle lock, as you do not
have control of the engine speed.
In the event of an emergency, switch off
the engine immediately – move the slide
control / momentary stop switch to 0 or
STOP.
Warning!
The rotating cutting attachment may
fling foreign objects directly or by ricochet a great distance.
To reduce the risk of eye and other injury
always wear proper eye protection (see
the chapter on "Proper Clothing") and
ensure that bystanders are at least
50 feet (15 m) away. To reduce the risk
of damage to property, also maintain this
distance from such objects as vehicles
or windows. Any coworkers who must be
in the restricted area should also wear
goggles or protective glasses. Stop the
engine immediately if you are
approached.
Warning!
Before you start work,
examine the area for
stones, glass, fence wire,
metal, trash or other solid
objects. The cutting
attachment could throw
objects of this kind.
10
FS 40, FS 40 C, FS 50, FS 50 C
English
Warning!
This trimmer is normally to be used at
ground level with the cutting attachment
parallel to the ground. Use of a trimmer
above ground level or with the cutting
attachment perpendicular to the ground
may increase the risk of injury, since the
cutting attachment is more fully exposed
and the power tool may be more difficult
to control.
Warning!
During cutting, check the tightness and
the condition of the cutting attachment
at regular short intervals with the engine
and attachment stopped. If the behavior
of the attachment changes during use,
stop the engine immediately, wait until
the cutting attachment stops, and check
the nut securing the attachment for
tightness and the head for cracks, wear
and damage.
Warning!
A loose head may vibrate, crack, break
or come off the trimmer, which may
result in serious or fatal injury. Make
sure that the cutting attachment is properly tightened. Use the wrench supplied
or one of sufficient length to obtain the
proper torque. If the head loosens after
being properly tightened, stop work
immediately. The retaining nut may be
worn or damaged and should be
replaced. If the blade or head continues
to loosen, see your STIHL dealer. Never
use a trimmer with a loose cutting
attachment.
Warning!
Replace a cracked, damaged or wornout head or a cracked, bent, warped,
damaged, dull or worn out blade immediately, even if damage is limited to
superficial cracks. Such attachments
may shatter at high speed and cause
serious or fatal injury.
Warning!
If the head, blade or deflector becomes
clogged or stuck, always shut off the
engine and make sure the cutting
attachment has stopped before cleaning. Grass, weeds, etc. should be
cleaned off the blade or from around the
head at regular intervals.
Warning!
To reduce the risk of unintentional rotation of the cutting attachment and injury,
always shut off the engine and remove
the spark plug boot before replacing the
cutting attachment. To reduce the risk of
injury, always shut off the engine before
adjusting the length of the nylon line on
manually adjustable mowing heads.
Warning!
The gearbox becomes hot during operation. To reduce the risk of burn injury,
do not touch the gear housing when it is
hot.
Warning!
Never modify your muffler. Any modification could cause an increase in heat
radiation, sparks or sound level, thereby
increasing the risk of fire, burn injury or
hearing loss. You may also permanently
damage the engine. Have your muffler
serviced and repaired by your STIHL
servicing dealer only.
Warning!
The muffler and other parts of the
engine (e.g. fins of the cylinder, spark
plug) become hot during operation and
remain hot for a while after stopping the
engine. To reduce risk of burns, do not
touch the muffler and other parts while
they are hot. Keep the area around the
muffler clean. Remove excess lubricant
and all debris such as pine needles,
branches or leaves. Let the engine cool
down sitting on concrete, metal, bare
ground or solid wood (away from any
combustible substances.
Warning!
An improperly mounted or damaged cylinder housing or a damaged/deformed
muffler shell may interfere with the cooling process of the muffler. To reduce the
risk of fire or burn injury, do not continue
work with a damaged or improperly
mounted cylinder housing or a damaged/deformed muffler shell.
Your muffler is furnished with a spark
arresting screen designed to reduce the
risk of fire from the emission of hot
particles. Never operate your unit with a
missing or damaged spark arresting
screen. If your gas/oil mix ratio is correct
FS 40, FS 40 C, FS 50, FS 50 C
11
English
002BA354 KN
(i.e., not too rich), this screen will
normally stay clean as a result of the
heat from the muffler and need no
service or maintenance. If you
experience loss of performance and you
suspect a clogged screen, have your
muffler maintained by a STIHL servicing
dealer. Some state or federal laws or
regulations may require a properly
maintained spark arrestor for certain
uses. See the "Maintenance, Repair and
Storing" section of these Safety
Precautions. Remember that the risk of
a brush or forest fire is greater in hot or
dry conditions.
Warning!
Some STIHL power tools
are equipped with a catalytic converter, which is
designed to reduce the
exhaust emissions of the
engine by a chemical
process in the muffler. Due to this process, the muffler does not cool down as
rapidly as conventional mufflers when
the engine returns to idle or is shut off.
To reduce the risk of fire and burn injuries when using a catalytic converter,
always set your power tool down in the
upright position and never locate it
where the muffler is near dry brush,
grass, wood chips or other combustible
materials while it is still hot.
USING THE CUTTING ATTACHMENT
For an illustration of the various cutting
attachments and instructions on proper
mounting see the chapter on "Mounting
the Cutting Attachment" in your
instruction manual.
Warning!
To reduce the risk of severe or fatal
injury from blade contact and / or loss of
control, never attempt to use a metal
blade on this trimmer.
Using the Mowing Heads
Do not use with mowing line longer than
the intended length. With a properly
mounted deflector, the built-in linelimiting blade will automatically adjust
the line to its proper length.
Using the unit with an overly long nylon
cutting line increases the load on the
engine and reduces its operating speed.
This causes the clutch to slip
continuously and results in overheating
and damage to important components
(e.g. clutch, polymer housing
components). Such damage could,
among other things, cause the cutting
attachment to rotate at idle.
Mowing heads are to be used only on
trimmers equipped with a line-limiting
blade in the deflector in order to keep the
line at the proper length (see "Main
Parts" chapter in your instruction
manual).
If the lawn edges are planted with trees
or bordered by a fence etc., it is best to
use a nylon line head. It achieves a
"softer" cut with less risk of damaging
tree bark etc. than polymer blades.
However, the polymer-bladed STIHL
PolyCut produces a better cut if there
are no plants along the edge of the lawn.
Sharpening is not necessary, and worn
polymer blades are easily replaced.
Warning!
To reduce the risk of serious injury,
never use wire or metal-reinforced line
or other material in place of the nylon
cutting lines. Pieces of wire could break
off and be thrown at high speed toward
the operator or bystanders.
STIHL AutoCut mowing head
Nylon cutting cord advances
automatically when tapped against the
ground (TapAction).
STIHL PolyCut mowing head
Uses nonrigid, pivoting polymer blades.
12
FS 40, FS 40 C, FS 50, FS 50 C
Do not continue using the PolyCut if one
1
002BA073 KN
2
002BA074 KN
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 attachment 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 on one blade, always
replace all blades.
STIHL FixCut mowing head
Uses pre-cut lengths of nylon line.
Observe wear indicators.
Do not continue using the mowing head
if the raised moldings (1) on the base
are missing or worn – see right
illustration above. The mowing head
may otherwise shatter and flying objects
could result in injury to the operator or
bystanders. Install a new mowing head.
MAINTENANCE, REPAIR AND
STORING
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.
Warning!
Use only identical STIHL replacement
parts for maintenance and repair. Use of
non-STIHL parts may cause serious or
fatal injury.
Strictly follow the maintenance and
repair instructions in the appropriate
sections of your instruction manual.
English
Warning!
Always stop the engine and make sure
that the cutting attachment is stopped
before doing any maintenance or repair
work or cleaning the power tool. Do not
attempt any maintenance or repair work
not described in your instruction manual. Have such work performed by your
STIHL servicing dealer only.
Warning!
Use the specified spark plug, and make
sure it and the ignition lead are always
clean and in good condition. Always
press the spark plug boot snugly onto
the spark plug terminal of the proper
size. (Note: If the terminal has a detachable SAE adapter nut, it must be
securely attached). A loose connection
between the spark plug and the ignition
wire connector in the boot may create
arcing that could ignite combustible
fumes and cause a fire.
Warning!
Never test the ignition system with the
spark plug boot removed from the spark
plug or with a removed spark plug, since
uncontained sparking may cause a fire.
FS 40, FS 40 C, FS 50, FS 50 C
13
English
Warning!
Do not operate your power tool if the
muffler is damaged, missing or modified. An improperly maintained muffler
will increase the risk of fire and hearing
loss. Your muffler is equipped with a
spark-arresting screen to reduce the
risk of fire; never operate your power
tool if the screen is missing, damaged or
clogged. Remember that the risk of a
brush or forest fire is greater in hot or dry
weather.
In California, it is a violation of § 4442 or
§ 4443 or the Public Resources Code to
use or operate gasoline-powered tools
on forest-covered, brush-covered or
grass-covered land unless the engine’s
exhaust system is equipped with a
complying spark arrester that is
maintained in effective working order.
The owner/operator of this product is
responsible for properly maintaining the
spark arrester. Other states or
governmental entities/agencies, such as
the U.S. Forest Service, may have
similar requirements. Contact your local
fire agency or forest service for the laws
or regulations relating to fire protection
requirements.
Do not clean your machine with a
pressure washer. The solid jet of water
may damage parts of the machine.
Store the power tool in a dry and high or
locked location out of reach of children.
Before storing for longer than a few
days, always empty the fuel tank. See
chapter "Storing the Machine" in the
instruction manual.
Warning!
Never repair damaged or broken heads.
This may cause parts of the cutting
attachment to come off and result in
serious or fatal injuries.
Tighten all nuts, bolts and screws,
except the carburetor adjustment
screws, after each use.
14
FS 40, FS 40 C, FS 50, FS 50 C
Approved Combinations of Cutting Attachment, Deflector, Handle and Harness
546BA012 KN
1
2
6
7
5
Schnur/LINE 2
Schnur/LINE 1
3
4
Cutting Attachment Deflector Handle Harness
English
Approved Combinations
The complete combination includes:
– Cutting attachment
– Deflector
– Handle
– Shoulder strap (special accessory
only)
Select correct combination from the
table according to the cutting
attachment you intend to use. Read the
table horizontally from left to right.
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
Only mowing heads (1, 2, 3, 4) may be
used on trimmers with a curved drive
tube and loop handle.
Deflector
5 Deflector with blade for mowing
heads only (see "Mounting the
Deflector").
Handle
6 Loop handle
Harness
7 Shoulder strap may be used
Warning!
Based on the cutting attachment being
used:
Choose the proper deflector in order to
reduce the risk of injury from thrown
objects and contact with the cutting
attachment.
Make sure your unit is equipped with the
proper handle and harness in order to
reduce the risk of injury from loss of control and contact with the cutting
attachment.
Do not use rigid polymer blades, metal
cutting attachments or circular saw
blades on this unit.
Only mowing heads may be used on
loop-handled trimmers with a curved
drive tube.
FS 40, FS 40 C, FS 50, FS 50 C
15
English
2
1
546BA003 KN
545BA004 KN
546BA004 KN
A
1
2
232BA066 KN
4
546BA005 KN
3
Mounting the Loop Handle
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
Mounting the Deflector
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 6 in
(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.
N Turn the handle to the vertical
16
position.
FS 40, FS 40 C, FS 50, FS 50 C
English
546BA006 KN
232BA033 KN
1
2
3
4
1
232BA054 KN
2
3
4
3
Mounting the Cutting
Attachment
Preparations
N Lay your trimmer on sits back with
the loop handle and shroud pointing
down and the output shaft facing up.
Thrust Plate
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).
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.
The thrust plate is shipped with the
PolyCut 6-3 and FixCut 5-2. It is only
required for these mowing heads.
FS 40, FS 40 C, FS 50, FS 50 C
Mounting the Mowing Head
Keep the instruction sheet for the
mowing head in a safe place.
17
English
7
5
2
232BA053 KN
6
8
9
681BA018 KN
Schnur/LINE 2
Schnur/LINE 1
2
8
11
5
681BA019 KN
10
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.
Remove the locking pin.
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.
18
FS 40, FS 40 C, FS 50, FS 50 C
English
3
1
2
4
232BA074 KN
5
Block the drive 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).
Collar (see arrow) must engage the
mowing head's mounting hole.
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 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.
If the mounting nut turns too freely, fit a
new one.
FS 40, FS 40 C, FS 50, FS 50 C
Remove the locking pin.
19
English
1
232BA007 KN
2
Adjusting Nylon Line
STIHL AutoCut
N Hold the rotating mowing head
above the ground – tap it on the
ground once – about 1.2 in. (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 1 in. (2.5 cm).
If the mowing line is shorter than 1 in.
(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.
To reduce the risk of injury, always shut
off the engine before adjusting the
mowing line by hand.
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.
Fuel
This engine is certified to operate on
unleaded gasoline and the STIHL twostroke engine oil at a mix ratio of 50:1.
Your engine requires a mixture of highquality gasoline and two-stroke air
cooled engine oil.
Use mid-grade unleaded gasoline with a
minimum octane rating of 89 (R+M/2)
and no more than 10% ethanol content.
Fuel with a lower octane rating may
increase engine temperatures. This, in
turn, increases the risk of piston seizure
and damage to the engine.
The chemical composition of the fuel is
also important. Some fuel additives not
only detrimentally affect elastomers
(carburetor diaphragms, oil seals, fuel
lines, etc.), but magnesium castings and
catalytic converters as well. This could
cause running problems or even
damage the engine. For this reason
STIHL recommends that you use only
high-quality unleaded gasoline!
Gasoline with an ethanol content of
more than 10% can cause running
problems and major damage in engines
with a manually adjustable carburetor
and should not be used in such engines.
The ethanol content in gasoline affects
engine running speed – it may be
necessary to readjust the carburetor if
you use fuels with various ethanol
contents.
To reduce the risk of injury, always shut
off the engine before adjusting the
mowing line by hand.
20
FS 40, FS 40 C, FS 50, FS 50 C
English
002BA456 KN
Warning!
To reduce the risk of personal injury
from loss of control and / or contact with
the running cutting tool, do not use your
unit with incorrect idle adjustment. At
correct idle speed, the cutting tool
should not move.
If your power tool shows an incorrect
idle adjustment, have your STIHL dealer
check your power tool and make proper
adjustments and repairs.
The idle speed and maximum speed of
the engine change if you switch from a
fuel with a certain ethanol content to
another fuel with a much higher or lower
ethanol content.
This problem can be avoided by always
using fuel with the same ethanol
content.
Use only STIHL two-stroke engine oil or
equivalent high-quality two-stroke
engine oils that are designed for use
only in air cooled two-cycle engines.
We rec ommend STI HL H P Ultra 2-Cycle
Engine Oil since it is specially
formulated for use in STIHL engines.
Do not use BIA or TCW rated (twostroke water cooled) mix oils or other
mix oils that state they are for use in both
water cooled and air cooled engines
(e.g., outboard motors, snowmobiles,
chain saws, mopeds, etc.).
Take care when handling gasoline.
Avoid direct contact with the skin and
avoid inhaling fuel vapor. When filling at
the pump, first remove the container
from your vehicle and place the
container on the ground before filling. To
reduce the risk of sparks from static
discharge and resulting fire and/or
explosion, do not fill fuel containers that
are sitting in or on a vehicle or trailer.
The container should be kept tightly
closed in order to limit the amount of
moisture that gets into the mixture.
The machine‘s fuel tank should be
cleaned as necessary.
Fuel mix ages
Only mix sufficient fuel for a few days
work, not to exceed 3 months of storage.
Store in approved fuel-containers only.
When mixing, pour oil into the container
first, and then add gasoline. Close the
container and shake it vigorously by
hand to ensure proper mixing of the oil
with the fuel.
Gasoline
Oil (STIHL 50:1 or equivalent high-quality oils)
US gal. US fl.oz.
12.6
2 1/2 6.4
5 12.8
Dispose of empty mixing-oil containers
only at authorized disposal locations.
Fueling
Preparations
N Before fueling, clean the filler cap
and the area around it to ensure that
no dirt falls into the tank.
Always thoroughly shake the mixture in
the canister before fueling your
machine.
N Position the machine so that the
filler cap is facing up.
In order to reduce the risk of fire and
personal injury from escaping gas vapor
and fumes, remove the fuel filler cap
carefully so as to allow any pressure
build-up in the tank to release slowly.
One of two different filler caps is
installed as standard at the factory.
FS 40, FS 40 C, FS 50, FS 50 C
21
English
002BA418 KN
002BA419 KN
001BA218 KN
001BA219 KN
001BA224 KN
001BA220 KN
001BA221 KN
001BA222 KN
N Insert the cap – positioning marks
on the cap and the fuel tank opening
must line up.
N The cap should drop fully into the
opening in this position.
Toolless filler cap (with folding grip)
Threaded filler cap
Opening the toolless filler cap
N Raise the grip into an upright
position.
N Turn the cap counterclockwise
(approx. 1/4 turn).
N Remove fuel filler cap.
Refueling
Take care not to spill fuel while fueling
and do not overfill the tank. STIHL
recommends use of the STIHL filling
system (special accessory).
Closing the toolless filler cap
N While pressing the cap down, twist it
firmly clockwise as far as it will go
(approx. 1/4 turn).
N Fold down the grip.
22
With grip in an upright position:
FS 40, FS 40 C, FS 50, FS 50 C
English
001BA223 KN
001BA225 KN
001BA227 KN
001BA226 KN
002BA447 KN
002BA448 KN
Checking for proper closure
N The lug on the grip must engage
entirely in the recess (arrow), and
the grip must lie completely flush
with the top of the cap.
N Grip the cap and check for
tightness.
N If the cap can be moved, it is not
properly installed.
Misalignment of the cap parts
N If the cap does not drop fully into the
opening when the positioning marks
line up and/or if the cap does not
tighten properly when twisted, the
base of the cap may be rotated out
of position vis-à-vis the top.
N Such misalignment can result from
handling, cleaning or an improper
attempt at tightening.
Left: Base of improperly aligned
cap (with open space)
Right: Base of cap correctly posi-
tioned for installation
N To correct a misalignment, turn the
cap (with the grip up) until it drops
fully into the tank opening.
N Twist the cap counterclockwise as
far as it will go (approx. 1/4 turn) –
this will twist the base of the cap into
the correct position.
N Twist the cap clockwise, closing it
normally – see the sections
"Closing" and "Checking for proper
closure."
N If your cap still does not tighten
properly, it may be damaged or
broken; immediately stop use of the
unit and take it to your authorized
STIHL dealer for repair.
Opening the threaded filler cap
N Turn the cap counterclockwise until
it can be removed from the tank
opening.
N Remove the filler cap.
Refueling
Take care not to spill fuel while fueling
and do not overfill the tank. STIHL
recommends use of the STIHL filling
system (special accessory).
Closing the threaded filler cap
N Position cap.
N Turn the cap clockwise as far as it
will go and tighten it as securely as
possible by hand.
FS 40, FS 40 C, FS 50, FS 50 C
23
English
546BA007 KN
1
3
2
4
547BA015 KN
5
547BA016 KN
5
547BA017 KN
547BA018 KN
Starting / Stopping the
Engine
Controls
Version with loop handle
1 Throttle trigger lockout
2 Throttle trigger
3 Momentary stop switch with Run
and 0 = Stop positions.
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)
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 attachment 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
throttle trigger lockout lever.
Do not stand or kneel on the drive tube.
Function of momentary stop switch and
ignition system
The momentary 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 momentary
stop switch is moved to the 0 position,
the ignition is off. It is automatically
switched on again after the engine
comes to a standstill.
24
N Press in the choke lever (5) and turn
it to < at the same time.
FS 40, FS 40 C, FS 50, FS 50 C
English
547BA020 KN
547BA021 KN
N Hold the starter grip with your right
hand.
Models without Easy2Start
N Pull the starter grip slowly until you
feel it engage and then give it a brisk
strong pull.
Models with Easy2Start
N Pull the starter grip steadily.
Do not pull out the starter rope all the
way – it might otherwise break.
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 throttle trigger
lockout 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.
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
N Move the momentary stop switch in
the direction of 0 – the engine
stops – release the momentary stop
switch – t 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.
FS 40, FS 40 C, FS 50, FS 50 C
25
English
1
547BA022 KN
2
3
547BA023 KN
4
Operating Instructions Cleaning the Air Filter
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 enginemounted 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-ofservice periods – 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.
Replace damaged parts.
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.
26
FS 40, FS 40 C, FS 50, FS 50 C
English
547BA024 KN
Engine Management Adjusting the Carburetor
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 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
FS 40, FS 40 C, FS 50, FS 50 C
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.
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).
27
English
547BA028 KN
1
000BA039 KN
A
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.
If the cutting tool continues to rotate
when the engine is idling, have your
machine checked and repaired by your
servicing dealer.
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).
Spark Plug
If engine is down on power, difficult to
start or runs poorly at idling speed, first
check the spark plug.
Fit a new spark plug after approx. 100
operating hours or earlier if the
electrodes are badly eroded.
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.
Removing the Spark Plug
N Shut off the engine
The spark plug boot (2) sits inside the
cap (1).
The cap (1) protects the spark plug boot
from damage. Do not operate the
machine without a cap – replace a
damaged cap.
N Pull off the spark plug boot (2)
together with the cap (1).
N Unscrew the spark plug (3).
If the cap becomes detached while
pulling off the spark plug boot, see
"Installing the Spark Plug".
Checking the Spark Plug
N Clean dirty spark plug.
N Check 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:
– Too much oil in fuel mix.
– Dirty air filter.
– Unfavorable running conditions,
e.g. operating at part load.
28
FS 40, FS 40 C, FS 50, FS 50 C
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