Stihl Fs 90 R Manual

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STIHL FS 90
WARNING
Read Instruction Manual thoroughly 
before use and follow all safety 
precautions – improper use can 
cause serious or fatal injury.
ADVERTENCIA
Antes de usar la máquina lea y siga 
todas las precauciones de 
seguridad dadas en el manual de 
instrucciones – el uso incorrecto 
puede causar lesiones graves o 
mortales.
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							Instruction Manual
1 - 53
Manual de instrucciones
54 - 111 
						

							Original Instruction Manual Printed on chlorine-free paper
Printing inks contain vegetable oils, paper can be recycled. © ANDREAS STIHL AG & Co. KG, 2016
0458-260-8621-D. VA0.L15. 
0000000802_020_GB
FS 90, FS 90 R
English
1
{This instruction manual is protected by copyright. All rights reserved, especially the rights to reproduce, translate and process 
with electronic systems.
Contents
Allow only persons who fully understand 
this manual to operate your trimmer / 
brushcutter.
To receive maximum performance and 
satisfaction from your STIHL trimmer / 
brushcutter, 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 / 
brushcutter. 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 / brushcutter 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. Guide to Using this Manual 2
Safety Precautions and Working 
Techniques 3
Approved Combinations of Cutting 
Attachment, Deflector, Handle and 
Harness 17
Approved Power Tool Attachments 19
Mounting the Bike Handle 19
Mounting the Loop Handle 21
Adjusting the Throttle Cable 23
Fitting the Carrying Ring 23
Mounting the Deflector 23
Mounting the Cutting Attachment 24
Fuel 27
Fueling 28
Fitting the Harness 29
Balancing the Machine 30
Starting / Stopping the Engine 31
Transporting the Unit 33
Operating Instructions 35
Cleaning the Air Filter 35
Engine Management 36
Adjusting the Carburetor 36
Spark Arresting Screen in Muffler 36
Spark Plug 37
Engine Running Behavior 38
Lubricating the Gearbox 38
Storing the Machine 39
Sharpening Metal Cutting Blades 39
Maintaining the Mowing Head 40
Inspections and Maintenance by 
Dealer 41Maintenance and Care 42
Main Parts 44
Specifications 46
Maintenance and Repairs 47
Disposal 48
STIHL Incorporated Federal 
Emission Control Warranty 
Statement 48
STIHL Incorporated California 
Exhaust and Evaporative 
Emissions Control Warranty 
Statement 50
Trademarks 52 
						

							FS 90, FS 90 R
English
2
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.
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:
NA 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:
NLoosen the screw (1).
NLever (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.
WARNING
Indicates a hazardous situation which, if 
not avoided, could result in severe or 
fatal injury.
NOTICE
Indicates a risk of property damage, 
including damage to the machine or its 
individual components.
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 or the STIHL 
distributor for your area for assistance.Guide to Using this Manual
Fuel tank for gasoline 
and engine oil mixture
Press to operate decom-
pression valve
Manual fuel pump
Press to operate manual 
fuel pump
Filler hole for gear 
lubricant
Air intake summer mode
Air intake winter mode
Handle heating 
						

							FS 90, FS 90 R
English
3 The terminology utilized in this manual 
when referring to the power tool reflects 
the fact that different types of cutting 
attachments 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). A 
"brushcutter" designates a unit 
equipped with a rigid metal blade. Many 
FS models may be used as either a 
trimmer or a brushcutter – therefore, the 
power tool is referred in this manual as a 
"trimmer / brushcutter." Some smaller 
and / or lightweight FS models may only 
be used as a trimmer, i.e., they may not 
be used with metal blades.The term "clearing saw" indicates a 
high-powered trimmer / brushcutter that 
is particularly suited for use with a 
circular saw blade to clear saplings or 
small trees.
FS models with an "R" on the nameplate 
were originally configured (at the time of 
distribution) as a trimmer with a loop 
handle.
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.
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 and may cause blades to crack, chip or 
break. Thrown objects, including broken 
heads or blades, may result in serious or 
fatal injury to the operator or bystanders. 
STIHL does not recommend the use of 
rigid blades when cutting in stony areas.
Use your trimmer / brushcutter equipped 
with the appropriate cutting attachment 
only for cutting grass, brush, wood 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 / brushcutters. 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.
Safety Precautions and 
Working Techniques
Because a trimmer / 
brushcutter is a high-
speed, fast-cutting power 
tool sometimes equipped 
with sharp cutting blades, 
special safety precau-
tions must be observed to 
reduce the risk of per-
sonal 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. 
						

							FS 90, FS 90 R
English
4 Safe use of a trimmer / brushcutter 
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.
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 elements 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
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. 
						

							FS 90, FS 90 R
English
5
WARNING
Be particularly alert and cautious when 
wearing hearing protection because 
your ability to hear warnings (shouts, 
alarms, etc.) is restricted.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.
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.
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. 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 Z87 "+" (or your 
applicable national stand-
ard). 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.
Wear an approved safety 
hard hat to reduce the 
risk of injury to your head 
when there is a danger of 
head injuries.
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.
Always wear heavy duty 
work gloves (e.g. made of 
leather or other wear 
resistant material) when 
handling the machine 
and metal blades. 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.
Good footing is very 
important. Wear sturdy 
boots with nonslip soles. 
Steel-toed safety boots 
are recommended. 
						

							FS 90, FS 90 R
English
6 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 / brushcutter 
down. When transporting it in a vehicle, 
properly secure it to prevent turnover, 
fuel spillage and damage to the unit. 
STIHL recommends that you keep metal 
blades covered with the transport guard 
(optional accessory).
Fuel
Your STIHL power tool uses an oil- 
gasoline mixture for fuel (see the 
chapter on "Fuel" of your instruction 
manual).
WARNING
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
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.
WARNING
See also the "Fueling" chapter in your 
Instruction Manual for additional 
information.
389BA019 KN
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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 combus-
tible fuel vapor may 
escape from the fuel 
system.
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.
Unit vibrations can cause 
an improperly tightened 
fuel filler cap to loosen or 
come off and spill quanti-
ties of fuel. In order to 
reduce the risk of fuel 
spillage and fire, tighten 
the fuel filler cap by hand 
as securely as possible. 
						

							FS 90, FS 90 R
English
7 Before Starting
WARNING
Always check your power tool for proper 
condition and operation before starting, 
particularly the throttle trigger, throttle 
trigger lockout, slide control / 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.
WARNING
Check fuel system for leaks, especially 
the visible parts, e.g., filler cap, hose 
connections, manual fuel pump (only for 
power tools equipped with a manual fuel 
pump). Do not start the engine if there 
are leaks or damage – risk of fire! Have 
the machine repaired by a servicing 
dealer before using it.
WARNING
Never operate your power tool if it is 
damaged, improperly adjusted or 
maintained, or not completely or 
securely assembled.
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.
WARNING
The cutting attachment must be properly 
tightened and in safe operating 
condition. Inspect for loose parts (nuts, 
screws, etc.) and for cracked or 
damaged heads or cracked, bent, 
warped or damaged blades. Replace 
damaged heads or blades before using 
the power tool. Always keep blades 
sharp.
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
As can be seen in that chart, some 
cutting attachments may require you to 
change your deflector, handle and / or 
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).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 Combi-
nations of Cutting 
Attachment, 
Deflector, Handle 
and Harness".) 
						

							FS 90, FS 90 R
English
8 Arrows on the deflector (A) and limit 
stop (B) (as seen from the underside) 
show the correct direction of rotation of 
the cutting attachment. When viewed 
from above, however, the cutting 
attachment rotates counterclockwise.
Adjust carrying harness and hand grip 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, practice 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.
WARNING
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.
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.
Make sure you always have good 
balance and secure footing.
A
000BA006 KN
B
000BA007 KN