STIHL Fs 40 C Owners Manual

							FS 40, FS 40 C, FS 50, FS 50 C
English
9 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 stop switch is used 
to stop the engine, it automatically 
springs back to the "on" position in order 
to allow easier restarting. 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.
WARNING
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.
WARNING
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 
002BA054 KN
1HYHUDWWHPSWWRRSHUDWH
\RXUSRZHUWRROZLWKRQH
KDQG/RVVRIFRQWURORI
WKHSRZHUWRROUHVXOWLQJLQ
VHULRXVRUIDWDOLQMXU\PD\
UHVXOW7RUHGXFHWKHULVN
RIFXWLQMXULHVNHHS
KDQGVDQGIHHWDZD\
IURPWKHFXWWLQJDWWDFK-
ment. Never touch a 
moving cutting attach-
ment with your hand or 
any other part of your 
body.
As soon as the engine is 
running, this product gen-
erates toxic exhaust 
fumes containing chemi-
cals, such as unburned 
hydrocarbons (including 
benzene) and carbon 
monoxide, that are 
known to cause respira-
tory problems, cancer, 
birth defects, or other 
reproductive harm. Some 
of the gases (e.g. carbon 
monoxide) may be color-
less and odorless. To 
reduce the risk of serious 
or fatal injury/illness from 
inhaling toxic fumes, 
never run the machine 
indoors or in poorly venti-
lated locations. 
						

							FS 40, FS 40 C, FS 50, FS 50 C
English
10 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 / 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 
15 m (50 feet) away. To reduce the risk 
of damage to property, also maintain this 
distance from such objects as vehicles 
or windows. Even maintaining a 
minimum distance of 15 meters cannot 
exclude all potential risks. 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
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 
or other 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 worn-
out 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.
15m (50ft)
,QVSHFWWKHZRUNDUHD7R
UHGXFHWKHULVNRILQMXU\
UHPRYHVWRQHVSLHFHVRI
PHWDODQGRWKHUVROLG
REMHFWVZKLFKFRXOGEH
WKURZQPHWHUVRUPRUH
E\WKHFXWWLQJDWWDFKPHQW
RUGDPDJHWKHFXWWLQJ
DWWDFKPHQWRURWKHUSURS-
erty (e.g. parked 
vehicles, windows). 
						

							FS 40, FS 40 C, FS 50, FS 50 C
English
11
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, such as dry 
brush, grass or wood chips.
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 
(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.
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 line-
limiting 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. 
						

							FS 40, FS 40 C, FS 50, FS 50 C
English
12 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.Do not continue using the PolyCut if one 
of the circular holes (1; arrow) becomes 
visible or if the projecting rim (2; arrow) 
has worn away. Install a new mowing 
head.
WARNING
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.
002BA354 KN
1
002BA073 KN
2
002BA074 KN 
						

							FS 40, FS 40 C, FS 50, FS 50 C
English
13
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 systemby pulling 
the starter rope with the spark plug boot 
removed from the spark plug or with a 
removed spark plug, since the ignition is 
normally in the "on" position and there is 
a risk that uncontained sparking may 
cause a fire.
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 of 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.
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.
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. 
						

							FS 40, FS 40 C, FS 50, FS 50 C
English
14
Approved Combinations
The complete combination includes:
–Cutting attachment
–Deflector
–Handle
–Shoulder strap (special accessory)
Select correct combination from the 
table according to the cutting 
attachment you intend to use.
WARNING
For safety reasons no other 
combinations are permitted – risk of 
accidents.
Cutting Attachments
Mowing heads
1STIHL AutoCut C 5-2
2STIHL AutoCut 5-23STIHL AutoCut C 6-2
4STIHL DuroCut 5-2
5STIHL PolyCut 6-3
Deflector
6Deflector with blade, for mowing 
heads
Handle
7Loop handle
Shoulder strap
8Shoulder 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.
Approved Combinations of Cutting Attachment, Deflector, Handle and Harness
Cutting Attachment Deflector Handle Shoulder Strap
0000-GXX-0381-A1
12
78
6
Schnur/LINE  2Schnur/LINE  13
54 
						

							FS 40, FS 40 C, FS 50, FS 50 C
English
15 Your new power tool comes with the 
loop handle mounted on the drive tube, 
but it must be turned and lined up to suit 
your requirements.
Adjusting the loop handle
Versions with screw (FS 40)
NUse a screwdriver or the 
combination wrench to loosen the 
screw (1) on the handle.
Versions with star knob (FS 50)
NLoosen the star knob (2) on the 
handle.
All versions
NTurn the handle to the vertical 
position.The loop handle can be adjusted to suit 
the height and reach of the operator and 
the application by changing 
distance (A).
Recommended distance (A): about 6 in 
(15 cm)
NSlide the handle to the required 
position.
NTighten down the screw or star knob 
so that the handle cannot be rotated 
on the drive tube.
NPush the deflector (1) over the 
clamp (2) as far as stop.
NInsert the nut (3) in the hex recess in 
the deflector – make sure the holes 
line up.
NInsert the screw (4) with washer and 
tighten it down firmly.
Mounting the Loop Handle
21
546BA003 KN
545BA004 KN
546BA004 KN
A
0RXQWLQJWKHHIOHFWRU
1
2
232BA066 KN
4
546BA005 KN
3 
						

							FS 40, FS 40 C, FS 50, FS 50 C
English
16
Placing power tool on the ground
NSwitch off the engine.
NLay your trimmer on its back with 
the loop handle and shroud pointing 
down and the output shaft facing up.
Thrust Plate
The thrust plate (1) is shipped with the 
DuroCut 5-2 and PolyCut 6-3. It is only 
required for these mowing heads.
STIHL AutoCut 5-2 mowing head, 
STIHL AutoCut C 5-2 mowing head
NPull the thrust plate (1), if fitted, off 
the shaft (2).
STIHL PolyCut 5-2 mowing head, 
STIHL FixCut 6-3 mowing head
NSlip the thrust plate (1) over the 
shaft (2) and engage the hex 
recess (3) on the external 
hexagon (4).Blocking the Shaft
NTo block the shaft, insert a suitable 
tool (5) through the holes (6) in the 
deflector and thrust plate – turn the 
thrust plate back and forth if 
necessary.
Fitting Mowing Head with Screw 
Mounting
Keep the instruction leaflet for the 
mowing head in a safe place.
Mounting the Cutting 
Attachment
546BA016 KN
232BA033 KN
1
2 3
4
6
6
546BA017 KN5 
						

							FS 40, FS 40 C, FS 50, FS 50 C
English
17 NScrew the mowing head 
counterclockwise on to the shaft (1) 
as far as stop.
NBlock the shaft.
NTighten down the mowing head 
firmly.
NOTICE
Remove the tool used to block the shaft.
Removing the Mowing Head
NBlock the shaft.
NUnscrew the mowing head 
clockwise.
Fitting Mowing Head without Screw 
Mounting
Keep the instruction leaflet for the 
mowing head in a safe place.STIHL AutoCut 5-2
NFit the spring (1) in the mowing 
head (2).
NWind the mowing line  (3) on to the 
spool (4).
NThread the nylon line through the 
sleeves and fit the spool in the head.
The individual steps are described in the 
instruction sheet supplied.NSlip the mowing head (2) over the 
shaft (5) and engage hex recess (7) 
on the external hexagon (6).
NFit the cap (8) on the mowing head 
– screw it clockwise on to the shaft 
as far as stop and tighten it down 
firmly.
1
002BA385 KN
1
232BA054 KN
23 4
3
7
5 2
232BA053 KN
68 
						

							FS 40, FS 40 C, FS 50, FS 50 C
English
18 STIHL AutoCut C 5-2
NSlip the mowing head (2) on to the 
shaft – as AutoCut 5-2.
NTurn the spool (9) clockwise until 
the two arrow heads line up – 
secure the spool in this position.
NInsert the cap (8) in the spool, press 
it down as far as stop and turn it 
clockwise at the same time.
NTurn the cap until you feel 
resistance and then tighten it down 
firmly by hand.STIHL PolyCut 6-3
NFit the thrust plate on the shaft.
NInsert the nut (10) in the mowing 
head.
NScrew the mowing head (11) 
clockwise on to the shaft (5) as far 
as stop.
NBlock the shaft.
NTighten down the mowing head 
firmly.
WARNING
If the mounting nut has become too 
loose, fit a new one.
NOTICE
Remove the tool used to block the shaft.
Remove the mowing head.
STIHL AutoCut
NHold the mowing head steady.
NUnscrew the cap counterclockwise.
STIHL PolyCut
NBlock the shaft.
NUnscrew the mowing head 
counterclockwise.
9
681BA018 KN
Schnur/LINE  2
Schnur/LINE  128
11
5
681BA019 KN
10