Stihl Fs 90 R Manual

							FS 90, FS 90 R
English
29
Opening the filler cap
NTurn the cap counterclockwise until 
it can be removed from the tank 
opening.
NRemove the filler cap.
Refueling
Take care not to spill fuel while fueling 
and do not overfill the tank.
Closing the filler cap
NPosition cap.
NTurn the cap clockwise as far as it 
will go and tighten it as securely as 
possible by hand.The type and style of the 
harness/shoulder strap depend on the 
market.
The use of the shoulder strap is 
described in the chapter on "Approved 
Combinations of Cutting Attachment, 
Deflector, Handle and Harness".
Shoulder Strap
NPut on the shoulder strap (1).
NA d j u s t  t h e  l e n g t h  o f  t h e  s t r a p  s o  t h a t  
the carabiner (2) is about a hand’s 
width below your right hip.
NBalance the machine – see 
"Balancing the Machine".
Full Harness
NPut on the harness (1) and close the 
locking plate (3).
NAdjust the length of the strap – with 
the machine attached, the 
carabiner (2) must be about a 
hand's width below your right hip.
NBalance the machine – see 
"Balancing the Machine".
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30
Attaching the unit to the harness
The type and style of the harness and 
carabiner (spring hook) depend on the 
market.
NAttach the carabiner (1) to the 
carrying ring (2) on the drive tube.NLoosen the screw (3).
Balancing the brushcutter
The unit is balanced differently, 
depending on the cutting attachment 
used.
Proceed as follows until the conditions 
specified under "Floating positions" 
have been met:
NAdjust the carrying ring.
NTighten the screw moderately.
NAllow the unit to hang freely.
NCheck the position obtained.Floating positions
Mowing tools (A) such as mowing 
heads, grass cutting blades and brush 
knives
Nshould just touch the ground.
Circular saw blades (B)
Nshould "hover" about 20 cm (8 in) 
above the ground.
When the correct floating position has 
been reached:
NTighten down the screw on the 
carrying ring firmly.
Balancing the Machine
A
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31
Detaching the unit from the harness
NPress down the bar on the 
carabiner (1) and pull the carrying 
ring (2) out of the carabiner.
Operating elements
Control handle on handlebar
1Throttle lever lock
2Throttle trigger
3Slide controlControl handle on shaft
1Throttle lever lock
2Throttle trigger
3Slide control
Slide control positions
4STOP-0 – engine off – ignition is 
switched off
5Operating position F – Run – engine 
is running or can start
6START – Start – the ignition is 
switched on – the engine can be 
started
Symbol on slide control
7h – Stop sign and arrow – to switch 
off the engine, push the slide control 
in the direction of the arrow at the 
stop sign (h) to STOP-0
Starting / Stopping the 
Engine
3STOP
56
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STOP
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							FS 90, FS 90 R
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32
Starting
NPress the throttle trigger lockout and 
throttle trigger in succession
NHold both triggers down
NMove the slide control to START 
and hold it in position too
NRelease the throttle trigger, slide 
control and throttle trigger lockout in 
succession = starting throttle 
position
NSet the choke knob (8)
NPress the manual fuel pump 
bulb (9) at least 5 times - even when 
bulb is filled with fuelStarting
NLay the machine on the ground in a 
secure position: It must rest on the 
engine support and the deflector for 
the cutting attachment
N(if present): Remove the transport 
guard on the cutting attachment
The cutting attachment must not touch 
the ground or any other objects – risk of 
accident!
NAssume a firm stance – possibilities: 
standing, bending or kneeling
NPress the machine firmly against 
the ground with the left hand – do 
not touch the throttle trigger or 
throttle trigger lockout while doing 
so – your thumb should be under the 
fan housing
NOTICE
Do not stand or kneel on the shaft!NGrab the starter grip with your right 
hand
NPull the starter grip slowly until you 
feel it engage and then give it a 
brisk, strong pull
NOTICE
Do not pull out the starter rope 
completely – risk of breakage!
NDo not let the starter grip snap back 
– guide it slowly back into the 
housing so that the starter rope can 
rewind properly
Ncrank until the engine starts – at the 
latest after the fifth time the starter 
rope is pulled, turn the choke knob 
to e
Ncontinue cranking
Once the engine is running
NBlip the throttle trigger, the slide 
control jumps to run ?F –  t h e  e n g i n e  
begins to idle
WARNING
If the carburetor has been set correctly, 
the cutting attachment should not rotate 
when the engine is idling!
The machine is now ready for use. gIf the engine is cold
eIf the engine is warm – even if the 
engine has already run but is still 
cold
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							FS 90, FS 90 R
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Switching off the engine
NPush the slide control in the 
direction of the arrow at the stop 
signh to STOP-0
At very low temperatures
As soon as engine is running:
NBlip the throttle trigger = disengage 
starting throttle position – the slide 
control jumps to runF – engine 
begins to idle
NPress the throttle trigger slightly
NLet the engine warm up briefly
If the engine does not start
Choke knob
If the choke knob was not returned to e 
in time after the engine turned over for 
the first time, then the engine has 
flooded.
NTurn the choke knob to e.
NMove the slide control, throttle 
trigger interlock and throttle trigger 
to the starting throttle position
NStart the engine – to do this, pull the 
starter rope briskly – 10 or 20 pulls 
may be needed 
If the engine still does not start
NSet slide control to STOP-0
NRemove the spark plug - see "Spark 
plug"
NDry the spark plugNCrank the engine several times with 
the starter – to clear the combustion 
chamber
NReplace the spark plug – see "Spark 
plug"
NSet the slide control to START
NTurn the choke knob to e – even if 
the engine is cold!
NRestart the engine
Adjusting the throttle cable
NCheck throttle cable adjustment – 
see "Adjusting the throttle cable"
If the tank has been drained completely
NAfter refueling, press the manual 
fuel pump bulb at least five times – 
even if it is full of fuel.
NSet choke lever depending on 
engine temperature
NRestart the engine
Using Transport Guard
The type of transport guard depends on 
the metal cutting attachment supplied 
with the machine. Transport guards are 
available as special accessories.
230 mm Grass Cutting Blades
Transporting the Unit
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							FS 90, FS 90 R
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34
250 mm Brush Knives
Circular Saw Blades
NDisconnect wire rod from the 
transport guard.
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							FS 90, FS 90 R
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35 NSwing wire rod outwards.
NFit transport guard on saw blade 
from below, making sure the limit 
stop is properly seated in the 
recess.
NSwing wire rod into position.
NHook wire rod to the transport 
guard.
During break-in period
A factory-new machine should not be 
run at high revs (full throttle off load) for 
the first three tank fillings. This avoids 
unnecessary high loads during the 
break-in period. As all moving parts 
have to bed in during the break-in 
period, the frictional resistances in the 
engine are greater during this period. 
The engine develops its maximum 
power after about 5 to 15 tank fillings.
During Operation
After a long period of full throttle 
operation, allow the engine to run for a 
short while at idle speed so that engine 
heat can be dissipated by the flow of 
cooling air. This protects engine-
mounted components (ignition, 
carburetor) from thermal overload.
After Finishing Work
Storing for a short period: Wait for the 
engine to cool down. Empty the fuel tank 
and keep the machine in a dry place, 
well away from sources of ignition, until 
you need it again. For longer out-of-
service periods – see "Storing the 
Machine".If there is a noticeable loss of engine 
power
NTurn the choke knob to g
NTake out the screw (1) and remove 
the filter cover (2). 
NClean away loose dirt from around 
the filter.
NGrip the filter element (3) at the 
cutout (arrow) in the filter 
housing (4) and remove it.
NFit a new filter element. As a 
temporary measure you can knock it 
out on the palm of your hand or blow 
it out with compressed air. Do not 
wash.
NReplace damaged parts.
Installing the filter
NInstall the filter element in the filter 
housing and fit the cover.
NInsert the screw and tighten it down 
firmly.
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							FS 90, FS 90 R
English
36 Exhaust emissions are controlled by the 
design of the fundamental engine 
parameters and components (e.g. 
carburation, ignition, timing and valve or 
port timing) without the addition of any 
major hardware.The carburetor of the machine has been 
adjusted for optimum performance and 
fuel efficiency in all operating states at 
the factory.
Setting the idle speed
Engine stops when idling
NLet the engine warm up for approx. 
3min
NSlowly turn idle speed screw (LA) 
clockwise until the engine runs 
smoothly – the cutting attachment 
must not rotate
Cutting attachment turns when idling
NTurn the idle speed screw (LA) 
slowly counterclockwise until the 
cutting attachment stops moving – 
then turn another 1/2 to 3/4 turn in 
the same direction
WARNING
If the cutting attachment continues to 
keep rotating in idle even after 
adjustment, have the machine checked 
by a servicing dealer.The muffler is equipped with a spark 
arresting screen.
NIf the engine is down on power, 
check the spark arresting screen in 
the muffler.
NWait for the muffler to cool down.
NMove the slide control to STOP-0.
NTake out the screw (1).
NTake out the screws (2) and remove 
the shroud (3).
Engine ManagementAdjusting the Carburetor
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							FS 90, FS 90 R
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37 NTake out the screw (4).
NLift the spark arresting screen (5) 
and pull it out.
NClean the spark arresting screen. If 
the screen is damaged or heavily 
carbonized, fit a new one.
NRefit the spark arresting screen.
NInsert screw and tighten it down 
firmly.
NInstall the shroud.If engine is down on power, difficult to 
start or runs poorly at idling speed, first 
check the spark plug.
Fit a new spark plug after approx. 100 
operating hours or earlier if the 
electrodes are badly eroded.
Wrong fuel mix (too much engine oil in 
the gasoline), a dirty air filter and 
unfavorable running conditions (mostly 
at part throttle etc.) affect the condition 
of the spark plug. These factors cause 
deposits to form on the insulator nose 
which may result in trouble in operation.
Removing the spark plug
NMove the slide control to STOP-0.
NPull off the spark plug boot (1).
NUnscrew the spark plug.
Checking the Spark Plug
NClean dirty spark plug.
NCheck electrode gap (A) and 
readjust if necessary – see chapter 
"Specifications."
NUse only resistor type spark plugs of 
the approved range.
Rectify problems which have caused 
fouling of spark plug:
–too much oil in fuel mix,
–dirty air filter,
–unfavorable running conditions, e.g. 
operating at part load.Spark Plug
1
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							FS 90, FS 90 R
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38
WARNING
To reduce the risk of fire and burn injury, 
use only spark plugs authorized by 
STIHL. Always press spark plug boot (1) 
snugly onto spark plug terminal (2) of the 
proper size. (Note: If terminal has 
detachable SAE adapter nut, it must be 
securely attached.) A loose connection 
between spark plug boot and ignition 
wire connector in the boot may create 
arcing that could ignite combustible 
fumes and cause a fire.
Installing the spark plug
NScrew home the spark plug, fit the 
boot and press it down firmly.If engine running behavior is 
unsatisfactory even though the air filter 
is clean and the carburetor is properly 
adjusted, the cause may be the muffler.
Have the muffler checked for 
contamination (carbonization) by your 
servicing dealer.
STIHL recommends that you have 
servicing and repair work carried out 
exclusively by an authorized STIHL 
servicing dealer.NCheck the grease level regularly – 
about every 25 hours of operation.
NUnscrew the filler plug (1). If no 
grease can be seen on the inside of 
the filler plug, screw the tube (2) of 
STIHL gear lubricant (special 
accessory) into the filler hole.
NSqueeze up to 5 g (1/5 oz) grease 
into the gearbox.
NOTICE
Do not completely fill the gearbox with 
grease.
NRemove the tube of grease (2).
NRefit the filler plug and tighten it 
down firmly.
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