Stihl Fs 90 R Manual

							FS 90, FS 90 R
English
9 Models with bike handle
Right hand on control handle, left hand 
on left handle.
Models with loop handle
Left hand on loop handle, right hand on 
control handle, even if you are left-
handed.
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.
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.
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  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 attach-
ment. Never touch a 
moving cutting attach-
ment with your hand or 
any other part of your 
body.
002BA055 KN
002BA054 KN
$VVRRQDVWKHHQJLQHLV
UXQQLQJWKLVSURGXFWJHQ-
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 90, FS 90 R
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, shut off 
the engine immediately – move the slide 
control / stop switch to 0 or STOP.
WARNING
WARNING
The rotating cutting attachment may 
fling foreign objects directly or by 
ricochet a great distance.T o  r e d u c e  t h e  r i s k  o f  e y e  a n d  o t h e r  i n j u r y  
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. Even maintaining a 
minimum distance of 15 meters cannot 
exclude the potential danger. 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 / brushcutter is normally to 
be used at ground level with the cutting 
attachment parallel to the ground. Use of 
a trimmer / brushcutter 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. Never use your trimmer / 
brushcutter as a hedge trimmer.
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 blade or head for 
cracks, wear and damage.
WARNING
A loose blade or head may vibrate, 
crack, break or come off the trimmer / 
brushcutter, 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 
blade or 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 / brushcutter 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  The cutting attachment 
continues to rotate for a 
short period after the 
throttle trigger is released 
(flywheel effect.)
Inspect the work area: To 
reduce the risk of injury, 
remove stones, pieces of 
metal and other solid 
objects which could be 
thrown 15 meters or more 
by the cutting attachment 
or damage the cutting 
attachment and property 
(e.g. parked vehicles, 
windows).
15m (50ft) 
						

							FS 90, FS 90 R
English
11 superficial cracks. Such attachments 
may shatter at high speed and cause 
serious or fatal injury.
WARNING
When using rigid blades, avoid cutting 
close to fences, sides of buildings, tree 
trunks, stones or other such objects that 
could cause the power tool to kick out or 
could cause damage to the blade. 
STIHL recommends use of the nylon line 
heads for such jobs. In addition, be alert 
to an increased possibility of ricochets in 
such situations.
WARNING
If a rotating metal blade strikes a rock or 
other hard object, sparks may be 
created, which can ignite flammable 
materials under certain circumstances. 
Flammable materials can include dry 
vegetation and brush, particularly when 
weather conditions are hot and dry. 
When there is a risk of fire or wildfire, do 
not use metal blades around flammable 
materials or around dry vegetation or 
brush. Contact your local fire authorities 
or the U.S. Forestry Service if you have 
any question about whether vegetation 
and weather conditions are suitable for 
the use of a metal blade.
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 
(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. 
						

							FS 90, FS 90 R
English
12
WARNING
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 an FS model for which it is not 
authorized.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.
Mowing heads are to be used only on 
trimmers / brushcutters 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 SuperCut mowing head
Fresh line is advanced automatically. 
Frayed line is replaced by a simple 
adjustment (see instruction sheet 
supplied with mowing head).
STIHL AutoCut mowing head
Nylon cutting line advances 
automatically when tapped against the 
ground (TapAction).
STIHL TrimCut mowing head
Frayed line is replaced by a simple 
adjustment (see instruction sheet 
supplied with mowing head).
STIHL PolyCut mowing head
Uses either nylon lines or nonrigid, 
pivoting polymer blades.
Observe wear indicators. Some STIHL power tools 
are equipped with a cata-
lytic converter, which is 
designed to reduce the 
exhaust emissions of the 
engine by a chemical pro-
cess in the muffler. Due 
to this process, the muf-
fler does not cool down 
as rapidly as conven-
tional mufflers when the 
engine returns to idle or 
is shut off. To reduce the 
risk of fire and burn inju-
ries 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 com-
bustible materials while it 
is still hot.
      
        
          
            
002BA354 KN 
						

							FS 90, FS 90 R
English
13
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.
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.Risk of Kickout (Blade Thrust) with all 
Rigid Cutting Blades
WARNING
This kickout (blade thrust) may cause 
loss of control of the power tool and may 
result in serious or fatal injury to the 
operator or bystanders. To reduce the 
risk of injury, extreme caution should be 
used when cutting with the shaded area 
of any rigid blade.Using the Grass Cutting Blade
All kinds of grass and weeds can be 
easily cut with the grass cutting blade. 
The power tool is swept in an arc similar 
to a scythe.
WARNING
To reduce the risk of serious or fatal 
injury from blade breakage, never 
attempt to use this blade to cut woody 
materials.
The 4-tooth grass cutting blade is 
intended to cut grass and weeds. It has 
4 cutting knives with cutting edges on 
both sides, i.e. front and rear. When the 
cutting edges on one side become dull, 
the blade can be turned over to utilize 
the cutting edges on the other side.
The 8-tooth grass cutting blade is 
recommended for cutting fern or reed.
Both types of grass cutting blade have to 
be resharpened when all cutting edges 
are dull.
Using the Brush Knife
When fitted to the power tool, the brush 
knife is suitable for applications ranging 
from cutting matted grass to clearing 
weeds, wild growth and scrub.
002BA177 KN
.LFNRXWEODGHWKUXVWLV
WKHVXGGHQDQGXQFRQ-
trolled motion towards 
the operator's right or 
rear that can occur when 
the shaded area (espe-
cially the darkly shaded 
area) of a rotating blade 
comes in contact with a 
solid rigid object like a 
tree, rock, bush or wall. 
The rapid counterclock-
wise rotation of the blade 
may be stopped or 
slowed, and the cutting 
attachment may be 
thrown to the right or to 
the rear.
002BA135 KN
002BA355 KN 
						

							FS 90, FS 90 R
English
14 To cut wild growth and scrub, lower the 
rotating brush knife down onto the 
growth to achieve a chopping effect – 
but keep the tool below waist height at 
all times.
WARNING
Exercise extreme caution when using 
this method of cutting. The higher the 
cutting attachment is off the ground, the 
greater the risk of loss of control and of 
cuttings being thrown sideways.
Use the power tool like a scythe to cut 
grass, i.e. sweep it to and fro in an arc.
WARNING
When cutting woody materials, use the 
left side of the blade to avoid "kickout" 
(blade thrust) situations.
WARNING
Improper use of a brush knife may cause 
it to crack, chip or shatter. Thrown blade 
fragments may seriously or fatally injure 
the operator or bystanders. To reduce 
the risk of injury, avoid contact with hard 
or solid foreign objects such as stones, 
rocks or pieces of metal.
WARNING
When cutting young saplings or other 
woody materials up to 2 cm (3/4 in.) in 
diameter, use the left side of the blade to 
avoid "kickout" situations (see section 
on "Risk of kickout (blade thrust) with all 
rigid cutting blades"). Do not attempt to 
cut woody material with a larger 
diameter, since the blade may catch or 
jerk the power tool forward. This may 
cause damage to the blade or power tool 
or loss of control of the power tool, 
resulting in personal injury. Use a 
circular saw blade for such work.
WARNING
Inspect the brush knife at regular short 
intervals for signs of damage. Do not 
continue working with a damaged brush 
knife. Resharpen the brush knife 
regularly (when it has dulled noticeably).Using the Circular Saw Blade
Circular saw blades are suitable for 
thinning brush and cutting small trees up 
to a diameter of 4 cm (1 1/2 in.). Do not 
attempt to cut trees with larger 
diameters, since the blade may catch or 
jerk the trimmer / brushcutter forward. 
This may cause damage to the blade or 
loss of control of the power tool and 
result in serious injury. Use a chain saw 
for such work.
WARNING
To reduce the risk that the blade will 
crack and / or break, avoid all contact 
with stones, rocks or the ground. 
Sharpen blades in a timely manner as 
specified – dull teeth may cause the 
blade to crack or shatter.
When a trimmer / brushcutter with a 
circular saw blade is used to cut down 
small trees, STIHL recommends that the 
standard deflector be removed and 
002BA066 KN
000BA016 KN 
						

							FS 90, FS 90 R
English
15 replaced by the special limit stop 
deflector (see chapter on "Mounting the 
Deflector"). This limit stop helps to keep 
the unit positioned against the tree 
during the cutting process. 
Inexperienced users should place the 
left side of the stop against the tree trunk 
before beginning to cut. This will keep 
the trimmer / brushcutter against the tree 
during the cutting operation and will 
reduce the risk of loss of control and 
possible kickout (described above and 
briefly again below).
Before starting the cut, accelerate the 
engine up to full throttle. Perform cut 
with uniform pressure. STIHL 
recommends that the circular saw blade 
be applied to the right of the tree, using 
the non-shaded area of the blade, as 
shown in the illustration above.
WARNING
The risk of kickout is highest when 
cutting in the darker shaded area. To 
reduce the risk of kickout and resulting 
injury, do not use this area of the circular 
saw blade for cutting trees or shrubs. 
Special techniques using the lighter 
shaded areas of the blade to cut shrubs 
and trees should only be used by 
experienced operators with specialized 
training in the use and control of the 
trimmer / brushcutter.
WARNING
To reduce the risk of loss of control and 
serious injury to the operator or 
bystanders by a kickout, never use a 
circular saw blade on a trimmer / 
brushcutter with a loop handle, but 
rather only on one with a bicycle handle.
When felling small trees, maintain a 
distance of at least two tree lengths from 
the nearest coworker.
WARNING
In order to reduce the risk of injury from 
thrown objects or operator contact with 
the blade or head, be sure to remount 
the standard deflector when no longer 
using a circular saw blade.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.
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.
Wear gloves when handling or 
performing maintenance on blades.
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 
002BA214 ST
002BA068 KN 
						

							FS 90, FS 90 R
English
16 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.
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 cutting 
attachments by welding, straightening or 
modifying the shape. This may cause 
parts of the cutting attachment to come 
off and result in serious or fatal injuries.
Keep blades sharp. 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 90, FS 90 R
English
17
Approved Combinations of Cutting Attachment, Deflector, Handle and Harness
Cutting Attachment Deflector, Limit Stop Handle Shoulder Strap/Harness
7
12
34
56
89
10
11
14
1318
15
2224
0000-GXX-0385-A0
12
16
17
1920
21
1920
21
21
23
23
24
24
25 
						

							FS 90, FS 90 R
English
18
Approved Combinations
The complete combination includes:
–Cutting attachment
–Deflector
–Handle
–Shoulder strap/harness
Select correct combination from the 
table according to the cutting 
attachment you intend to use.
WARNING
For safety reasons only the cutting 
attachments, deflectors, handles and 
harnesses shown in each row of the 
table may be used together. No other 
combinations are permitted because of 
the risk of accidents.
Cutting Attachments
Mowing heads
1STIHL SuperCut 20-2
2STIHL AutoCut C 25-2
3STIHL AutoCut 25-2
4STIHL AutoCut 36-2
5STIHL TrimCut 31-2
6STIHL DuroCut 20-2
7STIHL PolyCut 20-3
Metal cutting attachments
8Grass cutting blade 230-4
(230 mm dia.)
9Grass cutting blade 230-8
(230 mm dia.)10Brush knife 250-3
(250 mm dia.)
11Scratcher tooth circular saw blade 
200
(200 mm dia.)
12Chisel tooth circular saw blade 200
(200 mm dia.)
WARNING
Non-metal grass cutting blades, brush 
knives and circular saw blades are not 
approved.
Deflectors, Limit Stop
13Deflector for mowing heads
14Deflector with
15skirt and blade, for mowing heads
16Deflector without skirt and blade, for 
metal cutting attachments 8 to 10
17Limit stop for circular saw blades
Handles
18Loop handle
19Loop handle with
20Barrier bar
21Bicycle handle
Shoulder Strap/Harness
22Shoulder strap may be used
23Shoulder strap must be used
24Full harness may be used
25Full harness must 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. 
Use grass cutting metal blades and 
brush knives on this unit only if equipped 
with a bike handle or a loop handle with 
barrier bar. 
Use circular saw blades on this unit only 
if equipped with a bike handle.
Do not use rigid plastic blades on this 
unit.