Stihl FS 100 RX User manual

Instruction Manual
Manual de instrucciones
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.
STIH)
STIHL FS 100 RX
BA_U1_86_02.fm Seite 0 Donnerstag, 18. Januar 2007 11:55 11

1FS 100 RX
English / USA
BA_SE_167_001_01_08.fmPrinted on chlorine-free paper.
Printing inks contain vegetable oils; paper can be recycled.
© ANDREAS STIHL AG & Co. KG, 2007 0458 259 8621 B. M3,5. G7. CP. Printed in USA
STIHl
Contents
Guide to Using this Manual .............. 2
Safety Precautions and Working
Techniques ....................................... 3
Mounting the Loop Handle ............. 13
Adjusting the Throttle Cable ........... 14
Fitting the Carrying Eye .................. 14
Mounting the Cutting Tools ............. 15
4-MIX Engine .................................. 18
Fuel ................................................ 18
Fueling ............................................ 19
Fitting the Harness ......................... 20
Balancing the Brushcutter .............. 20
Starting / Stopping the Engine ........ 21
Operating Instructions .................... 24
Cleaning the Air Filter ..................... 24
Motor Management ........................ 25
Adjusting the Carburetor ................ 25
Spark Arresting Screen in Muffler ... 27
Checking the Spark Plug ................ 27
Lubricating the Gearbox ................. 28
Replacing Starter Rope
and Rewind Spring ......................... 29
Storing the Machine ........................ 32
Inspections and Maintenance by
Dealer ............................................. 32
Maintenance Chart ......................... 33
Parts and Controls .......................... 35
Specifications ................................. 36
Special Accessories ....................... 37
Maintenance and Repairs ............... 37
STIHL Incorporated Federal
Emission Control Warranty
Statement ....................................... 38
STIHL Incorporated California
Exhaust and Evaporative Emissions
Control Warranty Statement ........... 40
Trademarks .................................... 42
Allow only persons who understand this
manual to operate your trimmer.
To receive maximum performance and
satisfaction from your STIHL trimmer, it
is important that you read and under-
stand the maintenance and safety
precautions, starting on page 3, before
using your trimmer.
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 pre-
cautions 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.
STIHL's philosophy is to continually
improve all of its products. As a result,
engineering changes and improve-
ments are made from time to time. If the
operating characteristics or the appear-
ance of your trimmer differs from those
described in this manual, please contact
your STIHL dealer for information and
assistance.

2
English / USA
FS 100 RX
Pictograms
All the pictograms attached to the
machine are shown and explained in
this manual.
The operating and handling instructions
are supported by illustrations.
Symbols in text
The individual steps or procedures
described in the manual may be marked
in different ways:
:A bullet marks a step or procedure
without direct reference to an
illustration.
A description of a step or procedure that
refers directly to an illustration may
contain item numbers that appear in the
illustration.
Example:
Loosen the screw (1)
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 described below:
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.
Note or hint which is not essential
for using the machine, but may
improve the operator’s under-
standing of the situation and result
in better use of the machine.
Note or hint on correct procedure in
order to avoid damage to the
environment.
Equipment and features
This instruction manual may refer to
several models with different
features. Components that are not
installed on all models and related
applications are marked with an
asterisk (*). Such components may
be available as special accessories
from your STIHL dealer.
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. If the
operating characteristics or the
appearance of your machine differ from
those described in this manual, please
contact your STIHL dealer for
assistance.
Therefore some changes, modifications
and improvements may not be covered
in this manual.
Guide to Using this Manual

3FS 100 RX
English / USA
Warning!
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
owner's manual and the
safety instructions periodically.
Careless or improper use of any trimmer
may cause serious or fatal injury.
Have your STIHL dealer show you how
to operate your trimmer. Observe all
applicable local safety regulations,
standards and ordinances.
!Warning!
Do not lend or rent your trimmer without
the owner's manual. Be sure that any-
one using your trimmer understands the
information contained in this manual.
!Warning!
The use of any trimmer may be
hazardous. If the rotating cutting tool
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 tool. Thrown
objects or damaged cutting tools may
result in serious or fatal injury to the
operator or bystanders.
!Warning!
Minors should never be allowed to
use a trimmer. Bystanders, especially
children, and animals should not be
allowed in the area where a trimmer
is in use.
Never let the trimmer run unattended.
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 owner's
manual for a description of the controls
and function of the parts of your model
trimmer.
Safe use of a trimmer involves
1. the operator
2. the trimmer
3. the use of the trimmer.
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 judgement. Do not operate a
trimmer when you are fatigued.
Be alert - if you get tired while operating
your trimmer, take a break.
Tiredness may result in loss of control.
Working with any trimmer can be
strenuous. If you have any condition that
might be aggravated by strenuous work,
check with your doctor before operating
a trimmer.
Safety Precautions and
Working Techniques

4
English / USA
FS 100 RX
!Warning!
Prolonged use of a trimmer (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 white-
finger 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 engine 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 trimmer 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 pressures and
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 monitor closely 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 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 trimmer
may not protect the operator from all
foreign objects (gravel, glass, wire, etc.)
thrown by the rotating cutting tool.
Thrown objects may also ricochet and
strike the operator.
!Warning!
To reduce the risk of injury
to your eyes never
operate a trimmer unless
wearing goggles or
properly fitted safety
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 safety glasses.

5FS 100 RX
English / USA
!Warning!
Trimmer 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.
Protect your hands with
gloves when handling the
trimmer and the cutting
tool. Heavy-duty, nonslip
gloves improve your grip
and protect your hands.
Clothing must be sturdy
and snug-fitting, but allow
complete freedom of
movement. Avoid loose-
fitting jackets, scarfs,
neckties, jewelry, flared or
cuffed pants, unconfined longhair or
anything that could become caught on
branches, brush or moving parts of the
unit. Wear long pants made of heavy
material to protect your legs. Do not
wear shorts, pants, sandals or go bare
foot. Secure hair so it is above shoulder
level.
Good footing is most
important in trimmer work.
Wear sturdy boots with
nonslip soles. Steel-toed
safety boots are
recommended.
THE TRIMMER
For illustrations and definitions of the
trimmer parts see the chapter on "Parts
and Controls".
!Warning!
Never modify a trimmer in any way. Only
cutting tools supplied by STIHL or
expressly approved by STIHL for use
with the specific STIHL trimmer models
are authorized. Although certain
unauthorized cutting tools are useable
for the STIHL trimmer, their use may, in
fact, be extremely dangerous.
!Warning!
To reduce the risk
of injury to
operator from
blade contact,
never use any
metal cutting attachment on this trimmer
model.
THE USE OF THE TRIMMER
Transporting the trimmer
!Warning!
Always turn off the engine and make
sure the cutting attachment has stop-
ped before putting a trimmer down.
When transporting your trimmer in a
vehicle, properly secure it to prevent
turnover, fuel spillage and damage to the
trimmer.
Preparation for the use of the trimmer
Adjust hand grip according to
instructions in the owner's manual to suit
your size before starting work.
Always check your trimmer for proper
condition and operation before starting,
particularly the throttle trigger, throttle
trigger interlock (if applicable), stop
switch, cutting tool, and deflector.
Arrows on the deflector show the correct
direction of rotation of the cutting tool.
The throttle trigger must move freely
and always spring back to the idle
position. The cutting tool must be
properly tightened and in safe operating
condition. Inspect for loose parts (nuts,
screws, etc.).

6
English / USA
FS 100 RX
Symbols on Deflector
Symbols on deflector for nylon line
mowing heads only:
1 Arrow shows direction of rotation
of cutting tool
2 "Do not use any metal cutting
tools"
3"Use only mowing heads"
Fueling
Your STIHL trimmer uses an oil-gasoline
mixture for fuel (see the chapter on
"Fuel" of your owner's manual).
!Warning!
Gasoline is an extremely
flammable fuel. If spilled
and ignited by a spark or
other ignition source, it
can cause fire and serious
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 trimmer.
Fueling Instructions
!Warning!
Fuel your trimmer 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 gas tank depending
on the fuel used, the weather conditions,
and the venting system of the tank. 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 trimmer carefully so as to
allow any pressure build-up in the tank
to release slowly. Never remove fuel
filler cap while 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
trimmer and check for leakage.
!Warning!
Check for fuel leakage while refueling
and during operation. If fuel or oil
leakage is found, do not start or run the
engine until leak is fixed and 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.
Cap with Grip
!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.
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
triangular marks on the grip of the cap
and on the fuel tank opening lining up.
Using the grip, turn the cap firmly
clockwise as far as it will go (approx. a
quarter turn).

7FS 100 RX
English / USA
Fold the grip flush with the
top of the cap. 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 neck,
the cap is not properly seated and
tightened and you must repeat the
above steps.
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 with as much force as
possible.
Starting
!Warning!
Your trimmer is a one-person machine.
Once started, it may fling foreign objects
for a great distance.
To reduce the risk of eye and other injury
insure that bystanders are at least
50 feet (15 m) away. Bystanders should
be encouraged to wear eye protection.
Stop the engine and cutting tool
immediately if you are approached. Start
and operate your trimmer without
assistance. For specific starting
instructions, see the appropriate section
of your manual. Place the trimmer on
firm ground or other solid surface in an
open area. Maintain a good balance and
secure footing.
!Warning!
To reduce the risk of injury from loss
of control, be absolutely sure that the
cutting tool 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
turn the cutting tool.
!Warning!
When you pull the starter grip, don't
wrap the starter rope around your hand.
Do not allow the grip to snap back, but
guide the starter rope to rewind it
properly. Failure to follow this procedure
may result in injury to hand or fingers
and may damage the starter
mechanism.
With the engine running but at idle,
attach the trimmer to the spring hook of
your harness (see appropriate chapter
of this manual).
15m (50ft)

8
English / USA
FS 100 RX
Catalytic converter
!Warning!
Some STIHL trimmer
models 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, the following specific
safety precautions must be observed.
!Warning!
Since a muffler with a catalytic converter
cools down less rapidly than conven-
tional mufflers, always set your trimmer
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.
Let the engine cool down sitting on
concrete, metal, bare ground or solid
wood (e.g. the trunk of a felled tree)
away from any combustible substances.
!Warning!
To reduce the risk of fire or burn injury,
let the unit cool down before refueling
your trimmer after use.
!Warning!
Never disassemble or modify your
muffler. The muffler could be damaged
and cause an increase in heat radiation
or sparks, thereby increasing the risk of
fire or burn injury. You may also
permanently damage the engine. Have
your muffler serviced and repaired by
your STIHL Servicing Dealer only.
!Warning!
To reduce the risk of fire or burn injury,
keep the area around the muffler clean.
Remove all debris such as pine needles,
branches or leaves.
!Warning!
An improperly mounted or damaged
cylinder housing or a damaged/
deformed muffler shell may interfere
with the cooling effect of the catalytic
converter. 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 catalytic
converter is furnished with screens
designed to reduce the risk of fire from
the emission of hot particles. Due to the
heat from the catalytic reaction, these
screens will normally stay clean 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.
Working Conditions
Operate and start your trimmer only
outdoors in a ventilated area. Operate
the trimmer under good visibility and
daylight conditions only. Work carefully.

9FS 100 RX
English / USA
!Warning!
Your trimmer produces
toxic exhaust fumes as
soon as the engine is
running. These gases
(e.g. carbon monoxide)
may be colorless and
odorless. To reduce the risk of serious or
fatal injury from inhaling toxic fumes,
never run the trimmer indoors or in
poorly ventilated locations.
!Warning!
Use of this product can generate dust
and fumes containing chemicals known
to cause respiratory disease, cancer,
birth defects, or other reproductive
harm. If you are unfamiliar with the risks
associated with the particular dust or
fume at issue, consult your employer,
governmental agencies such as OSHA
and NIOSH, and other sources on
hazardous materials. California and
some other authorities, for instance,
have published lists of substances
known to cause cancer, reproductive
toxicity, etc. Control dust and fumes at
the source where possible. In this regard
use good work practices and follow the
recommendations of OSHA/NIOSH and
occupational and trade associations.
When the inhalation of toxic dust and
fumes cannot be eliminated, the
operator and any bystanders should
always wear a respirator approved by
NIOSH / MSHA for the type of dust and
/ or fumes encountered."
!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.
Do not cut any material other than
weed or similar soft vegetation.
The cutting tools may be used only
for the operations described in your
manual.
Always hold the trimmer firmly with both
hands. Wrap your fingers tightly around
the handles, keeping the handles
cradled between your thumb and fore-
finger. Keep your hands in this position
to have your trimmer under control at all
times. Make sure your trimmer handles
and grip are in good condition and free
of moisture, pitch, oil or grease.
!Warning!
Never attempt to operate any trimmer
with one hand. Loss of control of the
trimmer resulting in serious or fatal injury
may result.
!Warning!
To reduce the risk of bodily injury
resulting from loss of control and/or
contact with the cutting tool, make sure
your unit is equipped with the proper
handle and harness for the type of
cutting attachment being used.
002BA056 KN

10
English / USA
FS 100 RX
!Warning!
To reduce the risk
of injury from
thrown objects and
blade contact,
never operate a
trimmer without a properly mounted
deflector. Keep the deflector (and the
skirt where appropriate) adjusted
properly at all times. 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. Be extremely cautious when
working on slopes or uneven ground.
Before cutting, inspect the
area for stones, glass,
pieces of metal, trash or
other solid objects. The
cutting attachment could
throw objects of this kind.
!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 trimmer may be more difficult to
control. Never use your trimmer as a
hedge trimmer.
Do not operate using the starting
throttle lock as you do not have control
of the engine speed. See section of your
owner's manual on the proper use of the
slide control.
If the cutting tool or deflector becomes
clogged or stuck, always turn off the
engine and make sure the cutting tool
has stopped, before cleaning. Grass,
weeds, etc. should be cleaned off the
cutting tool at regular intervals.
!Warning!
During cutting, check the tightness and
the condition of the cutting tool at
regular intervals. If the behavior of the
tool changes, stop the engine im-
mediately, and check the nut securing
the tool for tightness and the cutting
tool for cracks and damage. Replace
damaged cutting tools immediately.
Such tools may shatter at high speed
and cause serious or fatal injury.
!Warning!
Keep hands and feet
away from cutting tool.
Never touch a rotating
cutting tool with your hand
or any part of your body. It
continues to rotate for a
short period after the throttle trigger is
released (flywheel effect).
Important adjustments
!Warning!
To reduce the risk of personal injury from
loss of control or contact with the
running cutting tool, do not use a cutting
tool with incorrect idle adjustment.
At correct idle speed, the cutting tool
should not move. For directions on how
to adjust idle speed, see the appropriate
section of your owner's manual.
If you cannot set the correct idle speed,
have your STIHL dealer check your
trimmer and make proper adjustments
and repairs.

11FS 100 RX
English / USA
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 claim
warranty for a component which has
not been serviced or maintained
properly or if non-approved replace-
ment parts were used, STIHL may
deny warranty.
!Warning!
Use only STIHL replacement parts for
maintenance and repair.
Use of non-STIHL parts may cause
serious or fatal injury.
Follow the maintenance and repair
instructions in the appropriate section of
your owner's manual. Please refer to the
maintenance chart on the last pages of
this manual.
!Warning!
Always stop the engine and make sure
that the cutting tool is stopped before
doing any maintenance or repair work
or cleaning the trimmer. Do not attempt
any maintenance or repair work not
described in your owner's manual.
Have such work performed at your
STIHL service shop only.
!Warning!
Never repair damaged cutting tools by
welding, straightening or modifying the
shape. This may cause parts of the
cutting tool to come off and result in
serious or fatal injuries.
!Warning!
Check condition of cutting tool at regular
short intervals. If behavior of tool
changes, check it immediately for
tightness or any signs of cracks in
particular. Replace damaged or dull
cutting tools immediately, even if they
have only superficial cracks. If the
tool loosens after being properly
tightened, the retaining nut may be
worn or damaged and should be
replaced. If the tool continues to loosen,
see your STIHL dealer.
!Warning!
To reduce the risk of fire and burn
injuries, check fuel filler cap for leaks at
regular intervals. Use the specified
spark plug and make sure it and the
ignition lead are always clean and in
good condition.
!Warning!
Never test the ignition system with
ignition wire terminal removed from
spark plug or with unseated spark plug,
since uncontained sparking may cause
a fire.
!Warning!
To reduce the risk of fire and burn injury,
use only spark plugs authorized by
STIHL. Always press spark plug boot
snugly onto spark plug terminal of the
proper size. (Note: If terminal has
detachable SAE adapter nut, it must be
attached.) A loose connection between
spark plug terminal and ignition wire
connector in the boot may create arcing
that could ignite combustible fumes and
cause a fire. Keep spark plug clean, and
make sure ignition lead is in good
condition.
!Warning!
Do not operate your trimmer if the
muffler is damaged, missing or modified.
An improperly maintained muffler will
increase the risk of fire and hearing loss.
Never touch a hot muffler or burn will
result. If your muffler was equipped with
a spark-arresting screen to reduce the
risk of fire, never operate your trimmer if
the screen is missing or damaged. Do
not modify or remove any part of the
muffler or spark arresting screen.

12
English / USA
FS 100 RX
Remember that the risk of forest fires is
greater in hot or dry weather.
Tighten all nuts, bolts and screws,
except the carburetor adjustment
screws, after each use.
Additionally, the daily maintenance
schedule for your trimmer set forth in
your STIHL Owner's Manual should be
strictly followed.
For any maintenance please refer to the
maintenance chart and to the warranty
statement near the end of this manual.
Store trimmer in a dry, high or locked
location out of reach of children.
Before storing for longer than a few
days, always empty the fuel tank.
USING THE CUTTING TOOLS
For an illustration of the various cutting
tools and instructions on proper
mounting see the chapter on "mounting
the cutting tools" in your owner's
manual.
Using the mowing heads
The STIHL SuperCut, AutoCut, FixCut,
PolyCut and TrimCut mowing heads
produce a clean and tidy finish.
They are to be used only on brush-
cutters equipped with a limiter blade in
the deflector in order to keep the line at
the proper length (see "Parts and
Controls" chapter of this 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 with the polymer
blades.
!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.
000BA015 KN

13FS 100 RX
English / USA
STIHL SuperCut mowing head
Fresh line is advanced automatically.
Frayed line is replaced by a simple
adjustment (see instruction sheet
supplied with mowing head).
STIHL TrimCut and STIHL FixCut
mowing head
Frayed line is replaced by a simple
adjustment (see instruction sheet
supplied with mowing head).
STIHL AutoCut mowing head
Nylon cutting cord advances
automatically when tapped against the
ground.
STIHL PolyCut mowing head
Uses either nylon lines or nonrigid
plastic blades.
!Warning!
Three rectangular wear limit marks are
applied to the base (periphery) of the
Polycut. To reduce the risk of serious
injury from breakage of the head or
blades, the Polycut must not be used
when it has worn as far as one of these
marks. It is important to follow the
maintenance instructions supplied with
the head.
:Secure the loop handle (1)
approx. 8” (20cm) (A) forward of
the control handle (2).
:Line up the loop handle.
:Tighten down the screws.
Sleeve (3)
002BA177 KN
Mounting the Loop Handle

14
English / USA
FS 100 RX
A properly adjusted throttle cable is
the precondition for correct
operation in the full throttle, starting
throttle and idle positions.
Adjust the throttle cable only after
the unit is fully assembled – the
control handle must be in the normal
operating position.
:Use a suitable tool to push the slide
to the bottom of the slot (see
illustration).
:Press down the trigger interlock (1)
and squeeze the throttle trigger (2)
(full throttle) – this sets the throttle
cable correctly.
:For position of carrying eye1) see
"Parts and Controls"
:Place the clamp (1) with the
tapped hole on the left-hand side
of the drive tube.
:Squeeze the two ends of the clamp
together and hold in that position.
:Insert M 6 x 14 screw (2).
:Line up the carrying eye.
:Tighten down the screw firmly.
1) Included as standard or available as
special accessory
Adjusting the Throttle Cable
002BA163 KN
STOP
249BA017 KN
1
2
Fitting the Carrying Eye
002BA142 KN
1
2
1

15FS 100 RX
English / USA
Mowing tools
1STIHL Supercut 20-2
2STIHL Autocut 25-2
3STIHL Autocut C 25-2
4STIHL Trimcut 30-2
5STIHL PolyCut 20-3
6STIHL FixCut 25-2
!Warning!
STIHL brushcutters with a loop handle
without barrier bar may be used only
with the above mentioned mowing
heads with nylon line or plastic blades.
Preparations
:Lay your brushcutter on its back
with the gearhead facing upward
Blocking the Output Shaft
:Insert the stop pin* (2) or
screwdriver* (2) in the bore (3) in the
gearhead as far as stop, apply slight
pressure.
:Rotate nut or cutting tool on the
shaft (1) until the stop pin slips into
position and blocks the shaft.
After mounting the cutting tool,
remove the tool used to block the
shaft.
* Comes standard with the machine or
is available as special accessory –
see “Special Accessories”
Mounting the Cutting Tools
3
12
259BA010 KN
4
56

16
English / USA
FS 100 RX
Mounting the Mowing Head
Keep instruction sheet for mowing head
in a safe place.
:Screw the
STIHL SuperCut 20-2,
STIHL AutoCut 25-2,
STIHL AutoCut C 25-2
STIHL TrimCut 30-2,
counterclockwise onto the shaft (1)
as far as stop.
:Block the output shaft.
:Tighten down the mowing head.
Remove the tool used to block the
shaft.
STIHL FixCut 25-2
:Place the mowing head on the
thrust plate (2).
Shoulder (a) must engage hole (b)
in the mowing head.
:Block the output shaft.
:Push the thrust washer (3) over the
shaft (1)so that it locates against
the base.
Remove the tool used to block the
shaft.
Only the thrust ring (3) may be used
for mounting the mowing head. Do
not use the thrust washer and nut.
STIHL PolyCut 20-3
Use only the mowing head with the
stepped mounting shown above.
259BA011 KN
1
3
2
a
b
259BA012 KN

17FS 100 RX
English / USA
:Screw the mowing head onto the
shaft (1)counterclockwise.
:Block the output shaft.
:Tighten down the mowing head.
Remove the tool used to block the
shaft.
Mounting the Mowing Head
STIHL SuperCut 20-2,
STIHL AutoCut 25-2
STIHL AutoCut C 25-2
STIHL TrimCut 30-2,
STIHL PolyCut 20-3
:Block the output shaft.
:Tighten down the mowing head.
STIHL FixCut 25-2
:Loosen the thrust ring clockwise
and unscrew it from the shaft.
Adjusting Nylon Line
Note
The instruction sheet supplied with the
mowing head contains a detailed
description.
STIHL SuperCut
Fresh line is advanced automatically if
remaining line is still min. 21/2" (6cm)
long. The blade on the deflector trims
overlong line to the correct length.
STIHL AutoCut
:Hold the rotating mowing head
above the ground – tap it on the
ground once – about 11/4"(3 cm)
fresh line is advanced.
The blade on the deflector trims
overlong line to the correct length –
avoid tapping head more than once at a
time.
Line feed operates only if both lines
still have a minimum length of 1"
(2.5 cm).
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 nylon line by hand.
259BA013 KN
1

18
English / USA
FS 100 RX
The STIHL 4-MIX engine features gas
oil lubrication and must be run on a fuel
mixture of gasoline and engine oil.
It operates otherwise on the 4-stroke
principle.
This engine is certified to operate on
unleaded gasoline and the STIHL two-
stroke engine oil at a mix ratio of 50:1.
Your engine requires a mixture of high-
quality gasoline and quality two-stroke
air cooled engine oil.
Use mid-grade unleaded gasoline with a
minimum octane rating of 89 (R+M/2). If
the octane rating of the mid-grade
gasoline in your area is lower, use
premium unleaded fuel.
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
nationally recognized high-quality
unleaded gasoline!
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 recommend STIHL 50:1 two-stroke
engine oil since it is specially formulated
for use in STlHL engines.
Do not use BIA or TCW rated (two-
stroke 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,
chainsaws, 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 canister from
your vehicle and place the canister on
the ground before filling. Do not fill fuel
canisters that are sitting in or on a
vehicle.
The canister should be kept tightly
closed in order to avoid any moisture
getting into the mixture.
The machine‘s fuel tank and the canister
in which fuel mix is stored should be
cleaned as necessary.
4-MIX Engine Fuel

19FS 100 RX
English / USA
Fuel mix ages
Only mix sufficient fuel for a few days
work, not to exceed 3 months of storage.
Store in approved fuel-canisters only.
When mixing, pour oil into the canister
first, and then add gasoline. Close the
canister and shake it vigorously by hand
to ensure proper mixing of the oil with
the fuel.
Dispose of empty mixing-oil canisters
only at authorized disposal locations.
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.
In order to reduce the risk of burns
or other 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.
Opening the cap
:Raise the grip until it is upright.
:Turn the cap counterclockwise
(approx. a quarter turn).
:Remove the filler cap.
Gaso-
line
Oil (STIHL 50:1 or
equivalent high-quality oils)
US gal. US fl.oz
12.6
2 1/2 6.4
512.8
Fueling