Stihl FS 90 Manual

Guide to Using this Manual

Pictograms
The meanings of the pictograms attached to the machine are explained in this manual.

Depending on the model concerned, the following pictograms may be attached to your machine.

Fuel tank; fuel mixture of gasoline and engine oil

Operate decompression valve

Manual fuel pump

Operate manual fuel pump

Tube of grease

Intake air: Summer operation

Intake air: Winter operation

Handle heating

Symbols in text
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.

Engineering improvements
STIHL's philosophy is to continually improve all of its products. For this reason we may modify the design, engineering and appearance of our products periodically.

Therefore, some changes, modifications and improvements may not be covered in this manual.

Safety Precautions and Working Techniques

Some special safety precautions must be observed to reduce the risk of personal injury when operating this power tool because of the very high speed of its cutting attachment.

It is important you read and understand the instruction manual before using your power tool for the first time and keep the manual in a safe place for future reference. Non-observance of the safety precautions may result in serious or even fatal injury.

Observe all applicable local safety regulations, standards and ordinances.

If you have not used this type of power tool before: Have your dealer or other experienced user show you how to operate your power tool or attend a special course in its operation.

Minors should never be allowed to use a power tool.

Keep bystanders, especially children, and animals away from the work area.

When the power tool is not in use, shut it off so that it does not endanger others. Secure it against unauthorized use.

The user is responsible for avoiding injury to third parties or damage to their property.

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.

The use of noise emitting power tools may be restricted to certain times by national or local regulations.

To operate the power tool you must be rested, in good physical condition and mental health.

If you have any condition that might be aggravated by strenuous work, check with your doctor before operating a power tool.

Persons with pacemakers only: The ignition system of your power tool produces an electromagnetic field of a very low intensity. This field may interfere with some pacemakers. To reduce health risks, STIHL recommends that persons with pacemakers consult their physician and the pacemaker manufacturer before operating this tool.

Do not operate the power tool if you are under the influence of any substance (drugs, alcohol) which might impair vision, dexterity or judgment.

Depending on the cutting attachment fitted, use your power tool only for cutting grass, wild growth, shrubs, scrub, bushes, small diameter trees and similar materials.

Do not use your power tool for any other purpose since this may result in accidents.

Only use cutting attachments and accessories that are explicity approved for this power tool model by STIHL or are technically identical. If you have any questions in this respect, consult a servicing dealer. Use only high quality parts and accessories in order to avoid the risk of accidents and damage to the machine.

STIHL recommends the use of original STIHL replacement parts. They are specifically designed to match your model and meet your performance requirements.

Never attempt to modify your power tool in any way since this may increase the risk of personal injury. STIHL excludes all liability for personal injury and damage to property caused while using unauthorized attachments.

Do not use a pressure washer to clean the unit. The solid jet of water may damage parts of the unit.

The deflector on this power tool cannot protect the operator from all objects thrown by the cutting attachment (stones, glass, wire, etc.). Such objects may ricochet and then hit the operator.

Clothing and Equipment
Wear proper protective clothing and equipment.

Clothing must be sturdy but allow complete freedom of movement. Wear snug-fitting clothing, an overall and jacket combination, do not wear a work coat.

Avoid clothing that could get caught on branches or brush or moving parts of the machine. Do not wear a scarf, necktie or jewelry. Tie up and confine long hair (e.g. with a hair net, cap, hard hat, etc.).

Wear steel-toed safety boots with non-slip soles.

Sturdy shoes with non-slip soles may be worn as an alternative only when using mowing heads.

Wear a safety hard hat for thinning operations, when working in high scrub and where there is a danger of head injuries from falling objects. To reduce the risk of injury from thrown objects, always wear a face shield and safety glasses.

A face shield alone does not provide adequate eye protection.

Wear hearing protection, e.g. earplugs or ear muffs.

Wear heavy-duty gloves.

STIHL offers a comprehensive range of personal protective clothing and equipment.

Transporting the Power Tool

Always turn off the engine.

Carry the unit hanging from the shoulder strap or properly balanced by the drive tube. Fit transport guard on metal cutting attachments to avoid the risk of injury from blade contact

Transporting in a vehicle: Properly secure your power tool to prevent turnover, fuel spillage and damage.

Fueling

Gasoline is an extremely flammable fuel. Keep clear of naked flames. Do not spill any fuel – do not smoke.

Always shut off the engine before refueling.

Do not fuel a hot engine – fuel may spill and cause a fire.

Open the fuel cap carefully to allow any pressure build-up in the tank to release slowly and avoid fuel spillage.

Fuel your power tool only in wellventilated areas. If you spill fuel, wipe the machine immediately – if fuel gets on your clothing, change immediately.

Your power tool comes standard with either a screw-type or bayonet-type fuel cap.

After fueling, tighten down the screw-type fuel cap as securely as possible.

Insert the fuel cap with hinged grip (bayonet-type cap) correctly in the opening, turn it clockwise as far as stop and fold the grip down. This reduces the risk of unit vibrations causing the fuel cap to loosen or come off and spill quantities of fuel.

To reduce the risk of serious or fatal burn injuries, check for fuel leakage. If fuel leakage is found, do not start or run the engine until leak is fixed.

Before starting
Gasoline is an extremely flammable fuel. Keep clear of naked Check that your power tool is properly flames. Do not spill any assembled and in good condition – refer fuel – do not smoke. to appropriate chapters in the instruction manual.

• Use only an approved combination of cutting attachment, deflector, handle and harness. All parts must be assembled properly and securely.
• Slide control / stop switch must move easily toSTOP or 0
• Smooth action of throttle trigger interlock (if fitted) and throttle trigger – the throttle trigger must return automatically to the idle position.
• Check that the spark plug boot is secure – a loose boot may cause arcing that could ignite combustible fumesand cause a fire.
• Cutting tool or attachment: Check for correct and secure assembly and good condition.
• Check protective devices (e.g. deflector for cutting tool, rider plate) for damage or wear. Always replace damaged parts. Do not operate your machine with a damaged deflector or worn rider plate (lettering and arrows no longer legible).
• Never attempt to modify the controls or the safety devices in any way.
• Keep the handles dry and clean – free from oil and dirt – for safe control of the power tool.
• Adjust the harness and handle(s) to suit your height and reach. See chapters on "Fitting the Harness" and "Balancing the Trimmer/Brushcutter".

To reduce the risk of personal injury, do not operate your power tool if it is damaged or not properly assembled.

If you use a shoulder strap or full harness: Practise removing and putting down the machine as you would in an emergency. To avoid damage, do not throw the machine to the ground when practising.

Starting the engine
Start the engine at least 3 meters from the fueling spot, outdoors only.

Place the unit on firm ground in an open area. Make sure you have good balance and secure footing. Hold the unit securely. The cutting attachment must be clear of the ground and all other obstructions because it may begin to run when the engine starts.

Your power tool is a one-person unit. To reduce the risk of injury from thrown objects, do not allow other persons within a radius of 15 meters of your own position – even when starting.

To reduce the risk of injury, avoid contact with the cutting attachment.

Do not drop start the power tool – start the engine as described in the instruction manual. Note that the cutting attachment continues to run for a short period after you let go of the throttle trigger – flywheel effect.

Check idle speed setting: The cutting attachment must not rotate when the engine is idling with the throttle trigger released.

To reduce the risk of fire, keep hot exhaust gases and hot muffler away from easily combustible materials (e.g. wood chips, bark, dry grass, fuel).

Holding and Controlling the Power Tool
Always hold the unit firmly with both hands on the handles. Make sure you always have good balance and secure footing.

Models with bike handle

Right handle on control handle, left hand on left handle.

Models with loop handle

On units with a loop handle and barrier bar, left hand on loop handle, right hand on control handle, even if you are lefthanded.

During Operation

The correct engine idle speed is important to ensure that the cutting attachment stops rotating when you let go of the throttle trigger.

Check and correct the idle speed setting at regular intervals. If the cutting attachment still rotates at idle speed, have your dealer make proper adjustments or repairs. STIHL recommends a STIHL servicing dealer.

Take special care in slippery conditions – damp, snow, ice, on slopes or uneven ground.

Watch out for obstacles: Roots, tree stumps or holes which could cause you to trip or stumble.

Always stand on the ground while working, never on a ladder, work platform or any other insecure support.

Be particularly alert and cautious when wearing hearing protection because your ability to hear warnings (shouts, alarms, etc.) is restricted.

To reduce the risk of accidents, take a break in good time to avoid tiredness or exhaustion.

Work calmly and carefully – in daylight conditions and only when visibility is good. Stay alert so as not to endanger others.

Your power tool produces toxic exhaust fumes as soon as the engine is running. These fumes may be colorless and odorless and contain unburned hydrocarbons and benzol. Never run the engine indoors or in poorly ventilated locations, even if your model is equipped with a catalytic converter.

To reduce the risk of serious or fatal injury from breathing toxic fumes, ensure proper ventilation when working in trenches, hollows or other confined locations.

To reduce the risk of accidents, stop work immediately in the event of nausea, headache, visual disturbances (e.g. reduced field of vision), problems with hearing, dizziness, deterioration in ability to concentrate. Apart from other possibilities, these symptoms may be caused by an excessively high concentration of exhaust gases in the work area.

Operate your power tool so that it produces a minimum of noise and emissions – do not run the engine unnecessarily, accelerate the engine only for cutting.

To reduce the risk of fire, do not smoke while operating or standing near your power tool. Note that combustible fuel vapor may escape from the fuel system.

The dusts, vapor and smoke produced during operation may be dangerous to health. If the work area is very dusty or smoky, wear a respirator.

If your power 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 – see also "Before Starting".

Check the fuel system in particular for leaks and make sure the safety devices are working properly. Do not continue operating your power tool if it is damaged. In case of doubt, have the machine checked by your servicing dealer.

Do not operate your power tool with the starting throttle lock engaged – engine speed cannot be controlled in this position.

To reduce the risk of injury from thrown objects, never operate the unit without the proper deflector for the type of cutting attachment being used.

Inspect the work area: Stones, pieces of metal or other solid objects can be thrown and cause personal injury or damage the cutting attachment and property (e.g. parked vehicles, windows).

Special care must be taken when working in difficult, over-grown terrain.

When cutting high scrub, under bushes and hedges: Keep cutting tool at minimum height of 15 cm to avoid harming small animals.

Always shut off the engine before leaving the unit unattended.

Check the cutting attachment at regular short intervals during operation or immediately if there is a noticeable change in cutting behavior:

• Turn off the engine. Hold the unit firmly and wait for the cutting attachment to come to a standstill.
• Check condition and tightness, look for cracks.
• Check sharpness.
• Replace damaged or dull cutting attachments immediately, even if they have only superficial cracks.

Clean grass and plant residue off the cutting attachment mounting at regular intervals – remove any build up of material from the cutting attachment and deflector.

To reduce the risk of injury, shut off the engine before replacing the cutting attachment.

Do not continue using or attempt to repair damaged or cracked cutting attachments by welding, straightening or modifying the shape (out of balance).

This may cause parts of the cutting attachment to come off and hit the operator or bystanders at high speed and result in serious or fatal injuries.

When using mowing heads
Equip the deflector with the additional components specified in the instruction manual.

Use only the deflector with properly mounted line limiting blade to ensure the mowing lines are automatically trimmed to the approved length.

To reduce the risk of injury, always turn off the engine before adjusting the nylon line of manually adjustable mowing heads

Using the unit with over-long nylon cutting lines reduces the motor's operating speed. The clutch then slips continuously and this causes overheating and damage to important components (e.g. clutch, polymer housing components) – and this can increase the risk of injury from the cutting attachment rotating while the engine is idling.

When using metal cutting tools
STIHL recommends the use of original STIHL metal cutting attachments. They are specifically designed to match your model and meet your performance requirements.

Metal cutting attachments rotate at very high speed. The forces that occur act on the machine, the attachment and the material being cut.

Sharpen metal cutting attachments regularly as specified.

Unevenly sharpened metal cutting attachments cause out-of-balance which can impose extremely high loads on the machine and increase the risk of breakage.

Dull or improperly sharpened cutting edges can put a higher load on the cutting attachment and increase the risk of injury from cracked or broken parts.

Inspect metal cutting attachments for cracks or warping after every contact with hard objects (e.g. stones, rocks, pieces of metal). To reduce the risk of injury, remove burrs and other visible build-ups of material (use a file) because they may become detached and be thrown at high speed during operation.

To reduce the above-mentioned risks when using a metal cutting attachment, never use a metal cutting attachment with a diameter larger than specified. It must not be too heavy. It must be manufactured from materials of adequate quality and its geometry must be correct (shape, thickness).

To reduce the risk of injury, a metal cutting attachment not manufactured by STIHL must not be heavier, thicker, have a different shape or a diameter larger than the largest metal cutting attachment approved by STIHL for this power tool model.

Vibrations
Prolonged use of the power tool may result in vibration-induced circulation problems in the hands (whitefinger disease).

No general recommendation can be given for the length of usage because it depends on several factors.

The period of usage is prolonged by:

• Hand protection (wearing warm gloves)
• Work breaks

The period of usage is shortened by:

• Any personal tendency to suffer from poor circulation (symptoms: frequently cold fingers, tingling sensations).
• Low outside temperatures.
• The force with which the handles are held (a tight grip restricts circulation).

Continual and regular users should monitor closely the condition of their hands and fingers. If any of the above symptoms appear (e.g. tingling sensation in fingers), seek medical advice.

Maintenance and Repairs
Service the machine regularly. Do not attempt any maintenance or repair work not described in the instruction manual. Have all other work performed by a servicing dealer.

STIHL recommends that you have servicing and repair work carried out exclusively by an authorized STIHL servicing dealer. STIHL dealers are regularly given the opportunity to attend training courses and are supplied with the necessary technical information.

Only use high-quality replacement parts in order to avoid the risk of accidents and damage to the machine. If you have any questions in this respect, consult a servicing dealer.

STIHL recommends the use of genuine STIHL replacement parts. They are specifically designed to match your model and meet your performance requirements.

To reduce the risk of injury, always shut off the engine before carrying out any maintenance or repairs or cleaning the machine. – Exception: Carburetor and idle speed adjustments.

Do not turn the engine over on the starter with the spark plug boot or spark plug removed unless the slide control / stop switch is on STOP or 0 since there is otherwise a risk of fire from uncontained sparking.

To reduce the risk of fire, do not service or store your machine near open flames.

Check the fuel filler cap for leaks at regular intervals.

Use only a spark plug of the type approved by STIHL and make sure it is in good condition – see "Specifications".

Inspect the ignition lead (insulation in good condition, secure connection).

Check the condition of the muffler.

To reduce the risk of fire and damage to hearing, do not operate your machine if the muffler is damaged or missing.

Do not touch a hot muffler since burn injury will result.

Vibration behavior is influenced by the condition of the AV elements – check the AV elements at regular intervals.

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.

For any maintenance please refer to the maintenance chart and to the warranty statement near the end of the instruction manual.

Symbols on Deflectors
An arrow on the deflector shows the correct direction of rotation of the cutting attachments.

Use deflector in combination with mowing heads only. Do not use metal cutting attachments.

Harness / Strap
The harness is included in the scope of supply or available as a special accessory.

• Use a shoulder strap.
• With the engine running, attach the machine to the shoulder strap.

Grass cutting blades and brush knives must always be used in combination with a shoulder strap.

Circular saw blades must always be used in combination with a full harness with a quick-release system.

Mowing Head with Nylon Lines

Nylon line achieves a soft cut for edging and trimming around trees, fence posts, etc. – less risk of damaging tree bark.

To reduce the risk of injury, never use steel wire in place of the nylon cutting line.

STIHL Polycut Mowing Head with Polymer Blades
For mowing unobstructed edges of meadows (without posts, fences, trees or similar obstacles).

Check the wear limit marks!

If one of the wear limit marks on the PolyCut mowing head is worn through (arrow): Do not continue using the mowing head. Install a new one. There is otherwise a risk of injury from thrown parts of the head.

It is important to follow the maintenance instructions for the Polycut mowing head.

Grass Cutting Blade

Use for grass and weeds only – sweep the brushcutter in an arc like a scythe.

Improper use may damage the grass cutting blade – risk of injury from thrown parts.

Resharpen the grass cutting blade according to instructions when it has dulled noticeably.

Brush Knife
Suitable for cutting matted grass, wild growth and scrub, thinning young stands with a maximum stem diameter of 2 cm. To reduce the risk of personal injury, never attempt to cut thicker wood.

To cut wild growth and scrub, lower the brush knife down onto the growth to achieve shredding effect – do not use the cutting attachment above waist height.

Exercise extreme caution when using this method of cutting. The higher the cutting attachment is off the ground, the greater the risk of injury from cuttings being thrown sideways.

Use the brushcutter like a scythe (sweep it to the right and left) at ground level when cutting grass and thinning young stands.

Improper use of a brush knife may cause it to crack, chip or shatter – risk of injury from thrown parts.

To reduce the risk of injury it is essential to take the following precautions

• Avoid contact with stones, rocks, pieces of metal and other solid foreign objects.
• Never cut wood or shrubs with a stem diameter of more than 2 cm – use a circular saw blade for this purpose.
• Inspect the brush knife at regular short intervals for signs of damage. Do not continue working with a damaged brush knife. (when it has dulled noticeably) and have it balanced if necessary (STIHL recommends a STIHL servicing dealer).

Up to a stem diameter of 4 cm when used on brushcutters.

Up to a stem diameter of 7 cm when used on clearing saws.

Before starting the cut, accelerate the engine up to full throttle. Perform cut with uniform pressure.

Use circular saw blades only with a matching limit stop of the correct diameter.

To reduce the risk of blade damage, avoid contact with stones and the ground. Resharpen the blade properly in good time – dull teeth may result in the blade cracking and shattering and causing serious injury.

When felling, maintain a distance of at least two tree lengths from the next felling site.

Risk of kickout

The risk of kickout is highest in the black area of the blade: Do not use this area of the circular saw blade for cutting.

There is also a risk of kickout when using the lighter shaded areas of the blade: These areas of the blade should only be used by experienced operators with specialized training.

STIHL recommends that you use the non-shaded area of the circular saw blade. Always start the cut with this area of the blade.

Approved Combinations of Cutting Attachment, Deflector, Handle and Harness

Approved Combinations
Select correct combination from the table according to the cutting attachment you intend to use.

For safety reasons only the cutting attachments, deflectors, handles and harnesses/shoulder straps 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

1. STIHL SuperCut 20-2
2. STIHL AutoCut C 25--2
3. STIHL AutoCut 25-2
4. STIHL TrimCut 31-2
5. STIHL FixCut 25-2
6. STIHL PolyCut 20-3

Metal cutting attachments

7. Grass cutting blade 230-2
8. Grass cutting blade 230-4
9. Grass cutting blade 230-8
10. Grass cutting blade 250-40 Spezial
11. Brush knife 250-3
12. Scratcher tooth circular saw blade 200
13. Chisel tooth circular saw blade 200

Non-metal grass cutting blades, brush knives and circular saw blades are not approved.

Deflectors

14. Deflector only for mowing heads
15. Deflector with
16. Skirt and blade for all mowing heads only (see "Mounting the deflector")
17. Deflector without skirt and blade for all metal mowing attachments and brush knife
18. Limit stop for circular saw blades

Handles

19. Loop handle
20. Loop handlewith
21. Barrier bar
22. Bike handle

Harnesses

23. Shoulder strap may be used
24. Shoulder strap must be used
25. Full harness may be used
26. Full harness must be used

The following STIHL attachments may be mounted to the basic power tool:

¹⁾ Barrier bar must be mounted on the loop handle

²⁾ Unsuitable for units with bike handle

³⁾ Only of limited suitability for units with bike handle

⁴⁾ Shoulder strap is not necessary

⁵⁾ Use the handle hose supplied with the unit

Mounting the Bike Handle

Mounting the bike handle with swivelling handle support

• Pull out the wing screw – the washer (6) remains on the wing screw.
• Separate the clamp moldings – the springs (4 and 5) remain in the lower clamp.

Securing the handlebar

• Place the handlebar (7) in the lower clamp (1) so that distance A is no more than 15 cm (6 in).
• Place the upper clamp in position and hold both clamp moldings together.
• Push the wing screw with washer through the two clamps as far as stop – hold all parts together and secure them.

• Place the secured assembly on the handle support (8) with the wing screw at the side nearest the engine.
• Push the wing screw into the handle support as far as stop and then screw it down – but do not finally tighten yet.
• Line up the handlebar at a right angle to the drive tube – check distance A again.
• Tighten down the wing screw firmly.

Mounting the control handle

• Take out the screw (9) – the nut (10) remains in the control handle (11).
• Push the control handle onto the end of the handlebar (7) until the holes (13) line up – the throttle trigger (12) must point towards the gearhead.
• Insert the screw (9) and tighten it down firmly.

Fitting the throttle cable

Do not kink the throttle cable or lay it in tight radii – make sure the throttle trigger moves freely.

• Push the throttle cable (14) into the retainers (15).

Throttle cable adjustment

• Check adjustment of throttle cable – see chapter on "Adjusting the Throttle Cable".

For position of carrying ring see "Main Parts".

• Place the clamp (1) against the drive tubewith the tapped hole on the left (viewed from engine).
• Squeeze the two ends of the clamp together and hold in that position.
• Insert the M6x14 screw (2).
• Line up the carrying ring.
• Tighten down the screw firmly.

Mounting the Deflector

Mounting the Deflector

1. Deflector for mowing attachments
2. Deflector for mowing heads

Deflectors (1) and (2) are both mounted to the gearbox in the same way.

• Place the deflector on the gearbox flange.
• Insert the screws (3) and tighten them down firmly.

Fitting the Skirt and Blade

These parts must be fitted to the deflector (1) when you use a mowing head.

• Slide the lower guide slot of the skirt (4) onto the deflector (1) – it must snap into position.
• Push the blade (5) into the upper guide slot on the skirt and line it up with the first hole.
• Insert the screw and tighten it down firmly.

Mounting the Limit Stop

Always fit the limit stop (6) when you use a circular saw blade.

• Position the limit stop (6) on the gearbox flange.
• Insert the screws (7) and tighten them down firmly.

Mounting the Cutting Attachment

Preparations

• Lay your brushcutter on its back so that the cutting attachment mounting face is facing up.

Mounting hardware is not packed with machine
Only mowing heads can be mounted.

• Pull the hose (1) (protector for shipping) off the shaft (2).
• Go to "Mounting the mowing head".

If you want to mount a metal cutting attachment in place of a mowing head, you will need the following additional parts: Nut (3), rider plate (4) and thrust washer (5) (special accessories).

Mounting hardware is packed with machine
Mowing heads and metal cutting attachments may be mounted.

If the parts are packed with the machine

• Pull the hose (1) (protector for shipping) off the shaft (2).

The nut (3), rider plate (4) and thrust wsher (5) are in the parts kit supplied with the machine.

• Go to "Mounting the mowing head" or "Mounting the metal cutting attachment".

If the parts are mounted to the gearbox

• Go to "Removing the mounting hardware".

Removing the mounting hardware

• Block the shaft – see next chapter on "Blocking the output shaft".
• Use the combination wrench (6) – comes standard with machine or is available as special accessory – to unscrew the nut (3) clockwise (lefthand thread) from the shaft (2).
• Pull the thrust washer (5) off the shaft (2).

The rider plate (4) is in the parts kit supplied with the machine.

• Go to "Mounting the mowing head" or "Mounting the metal cutting attachment".

Blocking the output shaft

• Insert the stop pin (7) or screwdriver – come standard with machine or are available as special accessories – in the hole (8) in the gearbox as far as stop, and apply slight pressure.
• Rotate the nut or cutting attachment on the shaft (2) until the stop pin slips into position and blocks the shaft.

Mounting the Mowing Head
Keep the instruction sheet for the mowing head in a safe place.

STIHL SuperCut 20-2,
STIHL AutoCut 25-2,
STIHL AutoCut C 25-2,
STIHL TrimCut 31-2,
STIHL FixCut 25-2,
STIHL PolyCut 20-3

• Screw the mowing head counterclockwise on to the shaft (1) as far as stop.
• Block the shaft.
• Tighten down the mowing head.

Remove the tool used to block the shaft.

Removing the Mowing Head

• Block the shaft.

STIHL SuperCut 20-2,
STIHL AutoCut 25-2,
STIHL AutoCut C 25-2,
STIHL TrimCut 31-2,
STIHL FixCut 25-2,
STIHL PolyCut 20-3 N

• Unscrew the mowing head clockwise.

Adjusting Nylon Line
STIHL SuperCut
Fresh line is advanced automatically if remaining line is still at least 6 cm long. The blade on the deflector trims surplus line to the correct length.

STIHL AutoCut

• Hold the rotating mowing head above the ground – tap it on the ground once – about 3 cm fresh line is advanced.

The blade on the deflector trims surplus line to the correct length – avoid tapping the mowing head more than once at a time.

Line feed operates only if both lines still have a minimum length of 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 mowing line by hand.

Replacing Nylon Line or Cutting Blades
Refer to the instructions supplied with the mowing head.

Fit the approriate limit stop for circular saw blades 200 (6, 7) – see "Mounting the deflector".

Lay your brushcutter on its back with the cutting attachment mounting face pointing up: The cutting edges of (2), (4) and (5) may point in either direction. The cutting edges of (1), (3), (6) and (7) must point clockwise.

Direction of rotation is indicated by an arrow on the inside of the mowing attachment deflector or limit stop.

• Place the cutting attachment (8) on the thrust plate (9).

Collar (see arrow) must engage the cutting attachment's mounting hole.

• Fit the thrust washer (10) and rider plate (11) on the shaft (12).
• Block the drive shaft.
• Use the combination wrench (14) to screw the mounting nut (13) on to the output shaft counterclockwise and tighten it down firmly.

Remove the tool used to block the shaft.

Removing the metal cutting attachment

• Block the drive shaft.
• Unscrew the mounting nut clockwise.
• Take the parts off the shaft – donot remove the thrust plate (9).

If the mounting nut turns too freely, fit a new one.

4-MIX Engine

The STIHL 4-MIX engine features mixture lubrication and must be run on a fuel mixture of gasoline and engine oil.

It operates otherwise on the 4-stroke principle.

Fuel

This engine is certified to operate on unleaded gasoline and with the mix ratio 50:1.

Your engine requires a mixture of highquality premium gasoline and highquality two-stroke air-cooled engine oil.

Use premium branded unleaded gasoline with a minimum octane rating of 89 RON.

Note: Models equipped with a catalytic converter require unleaded gasoline. A few tankfuls of leaded gasoline can reduce the efficiency of the catalytic converter by more than 50%.

Fuel with a lower octane rating may result in preignition (causing "pinging") which is accompanied by an increase in engine temperature. This, in turn, increases the risk of the 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 as well. This could cause running problems or even damage the engine. For this reason it is essential that you use only high-quality fuels!

Fuels with different percentages of ethanol are being offered. Ethanol can affect the running behaviour of the engine and increase the risk of lean seizure.

Gasoline with an ethanol content of more than 10% can cause running problems and major damage in engines with a manually adjustable carburetor and should not be used in such engines.

Engines equipped with M-Tronic can be run on gasoline with an ethanol content of up to 25% (E25).

Use only STIHL two-stroke engine oil or equivalent high-quality two-stroke aircooled engine oils for mixing.

We recommend STIHL 50:1 two-stroke engine oil since it is specially formulated for use in STIHL engines.

Do not use BIA or TCW (two-stroke water cooled) mix oils!

Use only STIHL 50:1 heavy-duty engine oil or an equivalent quality twostroke engine oil for the fuel mix in models equipped with a catalytic converter.

Take care when handling gasoline. Avoid direct contact with the skin and avoid inhaling fuel vapour.

The canister should be kept tightly closed in order to avoid any moisture getting into the mixture.

The fuel tank and the canister in which fuel mix is stored should be cleaned from time to time.

Fuel mix ratio
Only mix sufficient fuel for a few days work, not to exceed 3 months of storage. Store in approved safety fuel-canisters only. When mixing, pour oil into the canister first, and then add gasoline.

Examples

Dispose of empty mixing-oil canisters only at authorized disposal locations.

Fueling

Preparations

• Before fueling, clean the filler cap and the area around it so that dirt cannot fall into the tank.
• Always position the machine so that the filler cap is facing upwards.

A number of different filler caps are installed as standard at the factory.

Cliplock filler cap (bayonet-type)

As soon as the engine runs

• Blip the throttle trigger. The slide control moves to the normal run position – and the engine settles down to idle speed.

Make sure the carburetor is correctly adjusted. The cutting attachment must not rotate when the engine is idling.

Your machine is now ready for operation.

Shut off the engine.

• Push the slide control in the direction of the arrow on the stop symbol (h) to STOP-0.

At very low outside temperatures:
As soon as the engine runs:

• Blip the throttle trigger to disengage thestarting throttle position. The slide control moves to the normal run position (F) – and the engine settles down to idle speed.
• Open the throttle slightly.
• Warm up the engine for a short period.

If the engine does not start
Choke knob
If you did not turn the choke knob to quickly enough after the engine began to fire, the combustion chamber is flooded.

• Turn the choke knob to .
• Set the slide control, lockout lever and throttle trigger to the starting throttle position.
• Start the engine by pulling the starter rope briskly – 10 to 20 pulls may be necessary.

If the engine still does not start

• Move the slide control toSTOP-0.
• Remove the spark plug – see "Spark Plug".
• Dry the spark plug.
• Crank the engine several times with the starter to clear the combustion chamber.
• Refit the spark plug – see "Spark Plug".
• Move the slide control toSTART.
• Set the choke knob to e – even if the engine is cold.
• Now start the engine.

Throttle cable adjustment

• Check adjustment of throttle cable – see chapter on "Adjusting the Throttle Cable".

Fuel tank run until completely dry

• After refueling, press the fuel pump bulb at least five times – even if the bulb is filled with fuel.
• Set the choke knob according to engine temperature.
• Start the engine.

Operating Instructions

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 enginemounted 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-ofservice perionds – see "Storing the Machine".

Cleaning the Air Filter
If there is a noticeable loss of engine power

• Turn the choke knob to
• Take out the screw (1) and remove the filter cover (2).
• Clean away loose dirt from around the filter.
• Grip the filter element (3) at the cutout (arrow) in the filter housing (4) and remove it.
• Fit 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.
• Replace damaged parts.

Installing the filter

• Install the filter element in the filter housing and fit the cover.
• Insert the screw and tighten it down firmly.

Engine Management

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.

Adjusting the Carburetor

The carburetor comes from the factory with a standard setting.

This setting provides an optimum fuel-air mixture under most operating conditions.

With this carburetor it is only possible to adjust the high speed and low speed screws within fine limits.

Standard Setting

• Shut off the engine
• Mount approved cutting tool or attachment.
• Check the air filter and clean or replace as necessary.
• Check that the throttle cable is properly adjusted – readjust if necessary – see chapter on "Adjusting the Throttle Cable".
• Check the spark arresting screen (not in all versions) and clean or replace as necessary.

• Carefully turn both adjusting screws counterclockwise as far as stop:
  • The high speed screw (H) is 3/4 turn open.
  • The low speed screw (H) is 3/4 turn open.
• Start and warm up the engine.
• Adjust idle speed with the idle speed screw (LA) so that the cutting attachment does not move.

Fine Tuning
A slight correction of the setting of the high speed screw (H) may be necessary if engine power is not satisfactory when operating at high altitude, sea level or after changing the working tool.

Rule of thumb:
Turn the high speed screw (H) about one quarter of a turn for every 1000 m (3300 ft) change in altitude.

Conditions for adjustment

• Carry out the standard setting without disturbing the high speed screw (H).
• Warm up the engine for about 3 minutes.
• Open the throttle wide.

At high altitude

• Turn the high speed screw (H) clockwise (leaner), no further than stop, until there is no further noticeable increase in engine speed.

At sea level

• Turn the high speed screw (H) counterclockwise (richer), no further than stop, until there is no further noticeable increase in engine speed.

It is possible that maximum engine speed may be reached with the standard setting.

Adjusting Idle Speed
It is usually necessary to change the setting of the idle speed screw (LA) after every correction to the low speed screw (L).

• Warm up the engine for about 3 minutes.

Engine stops while idling

• Turn the idle speed screw (LA) slowly clockwise until the engine runs smoothly – the cutting attachment must not move.

Cutting attachment runs when engine is idling

• Turn the idle speed screw (LA) counterclockwise until the cutting attachment stops running and then turn the screw about another 1/2 to 3/4 turn in the same direction.

If the working tool or cutting attachment continues to run when the engine is idling, have your machine checked and repaired by your servicing dealer.

Erratic idling behavior, engine stops even though setting of LA-screw has been corrected, poor acceleration
Idle setting is too lean

• Turn the low speed screw (L) counterclockwise, no further than stop, until the engine runs and accelerates smoothly.

Erratic idling behavior
Idle setting is too rich

• Turn the low speed screw (L) clockwise, no further than stop, until the engine runs and accelerates smoothly.

Spark Arresting Screen in Muffler

In some countries the muffler is equipped with a spark arresting screen.

• If the engine is down on power, check the spark arresting screen in the muffler.
• Wait for the muffler to cool down.
• Move the slide control to STOP-0.

• Take out the screw (1).

• Take out the screws (2) and remove the shroud (3).

• Take out the screw (4).
• Lift the spark arresting screen (5) and pull it out.
• Clean the spark arresting screen. If the screen is damaged or heavily carbonized, fit a new one.
• Refit the spark arresting screen.
• Insert the screw and tighten it down firmly.
• Fit the shroud.

Spark Plug

• If the engine is down on power, difficult to start or runs poorly at idle speed, first check the spark plug.
• Fit a new spark plug after about 100 operating hours – or sooner if the electrodes are badly eroded. Install only suppressed spark plugs of the type approved by STIHL – see "Specifications".

Removing the spark plug

• Move the slide control to STOP-0.
  

• Pull off the spark plug boot (1).
• Unscrew the spark plug.

Checking the spark plug

• Clean dirty spark plug.
• Check electrode gap (A) and readjust if necessary – see "Specifications".
• Rectify the problems which have caused fouling of the spark plug.

Possible causes are:

• Too much oil in fuel mix.
• Dirty air filter.
• Unfavorable running conditions.

If the spark plug comes with a detachable adapter nut (1), screw the adapter onto the thread and tighten it down firmly to reduce the risk of arcing and fire.

Installing the spark plug

• Screw the spark plug (3) into the cylinder and fit the boot (2) (press it down firmly).

Lubricating the Gearbox

• Check the grease level regularly – about every 25 hours of operation.
• Unscrew 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 for brushcutters (special accessory) into the filler hole.
• Squeeze up to 5 g grease into the gearbox.
  Do not completely fill the gearbox with grease.
• Remove the tube of grease (2).
• Refit the filler plug (1) and tighten it down firmly.

Replacing the Starter Rope and Rewind Spring

Replacing the Starter Rope

• Push the slide control in direction of arrow – to STOP-0.
• Take out the screws (1).
• Remove the starter cover (2) from the housing.

• Ease the spring clip (3) off the starter post.
• Remove the rope rotor with washer (4) and pawl (5).
• Remove the remaining rope from the rotor and starter grip.

• Tie a simple overhand knot in the new rope and then thread it through the top of the grip and the rope bushing (6).

Storing the Machine

For periods of 3 months or longer

• Drain and clean the fuel tank in a well ventilated area.
• Dispose of fuel properly in accordance with local environmental requirements.
• Run the engine until the carburetor is dry – this helps prevent the carburetor diaphragms sticking together.
• Remove, clean and inspect the cutting attachment.
• Thoroughly clean the machine – pay special attention to the cylinder fins and air filter.
• Store the machine in a dry and secure location – out of the reach of children and other unauthorized persons.

Sharpening Metal Cutting Blades

• Use a sharpening file (special accessory) to sharpen dull cutting attachments. In case of more serious wear or nicks: Resharpen with a grinder or have the work done by a dealer – STIHL recommends a STIHL servicing dealer.
• Resharpen frequently, take away as little material as possible: two or three strokes of the file are usually enough.
  
• Resharpen the cutters (1) uniformly – do not alter the contour or the parent blade (2) in any way.

See cutting attachment packaging for additional sharpening instructions.

Balancing

• After resharpening about 5 times, check the cutting attachment for out-of-balance on a STIHL balancer (special accessory) or have it checked by a dealer and rebalanced as necessary – STIHL recommends a STIHL servicing dealer.

Maintenance and Care

¹⁾ STIHL recommends a STIHL servicing dealer.

²⁾ not in all versions, market-specific

Main Parts

Definitions

1. Fuel Filler Cap
   For closing the fuel tank.
2. Carburetor Adjusting Screws
   For tuning the carburetor.
3. Starter Grip
   The grip of the pull starter, for starting the engine.
4. Spark Plug Boot
   Connects the spark plug with the ignition lead.
5. Muffler with Spark Arresting Screen
   Muffler reduces engine exhaust noise and diverts exhaust gases away from operator. Spark arresting screen is designed to reduce the risk of fire.
6. Bike Handle
   For easy control of the machine with both hands during cutting work.
7. Throttle Trigger
   Controls the speed of the engine.
8. Slide Control
   For starting throttle, run and stop. Keeps the choke partially open during starting and switches off the ignition to stop the engine.
9. Throttle Trigger Lockout
   Must be depressed before the throttle trigger can be activated.
10. Throttle Cable Retainer
    Secures the throttle cable to the drive tube.
11. Carrying Ring
    Connects the trimmer/brushcutter to the harness.
12. Fuel Pump
    Provides additional fuel feed for a cold start.
13. Choke Knob
    Eases engine starting by enriching mixture.
14. Air Filter Cover
    Encloses and protects the air filter element.
15. Fuel Tank
    For fuel and oil mixture.
16. Machine Support
    For resting machine on the ground.
17. Handle Support
    Connects the shaft and bike handle.
18. Wing Screw
    Locks handlebar in selected position.
19. Loop Handle
    For easy control of machine during cutting work.
20. Barrier Bar
    Helps keep user's feet and legs clear of the cutting tool.

1. Mowing Head
2. Deflector for Mowing Heads
3. Line Limiting Blade
4. Deflector with Skirt for all Mowing Attachments
5. Skirt
6. Metal Mowing Tool

Definitions

1. Mowing Head
   The cutting attachment, i. e. mowing head, for different purposes.
2. Deflector for Mowing Heads
   The deflector is designed to reduce the risk of injury from foreign objects flung backwards toward the operator by the cutting attachment and from contact with the cutting attachment.
3. Line Limiting blade
   Metal blade at the deflector in order to keep the line of the mowing head at the proper length.
4. Deflector with Skirt for all Mowing Attachments
   The deflector is designed to reduce the risk of injury from foreign objects flung backwards toward the operator by the cutting attachment and from contact with the cutting attachment. Is not designed to contain fragmented metal blades.
5. Skirt
   The skirt at the bottom of the deflector must be utilized as described in the chapter "Mounting the Deflector".
6. Metal Mowing Tool
   The cutting attachment, i. e. blade, made from metal for different purposes.

7. Circular Saw Blade
8. Limit Stop for Circular Saw Blade

Definitions

7. Circular Saw Blade
   Cutting attachment made of metal for cutting wood.
8. Limit Stop for Circular Saw Blade
   Is designed to position the brushcutter steady against the wood in order to reduce the risk of injury from loss of control from reactive forces such as thrust out.

Specifications
EPA / CEPA
The Emission Compliance Period referred to on the Emissions Compliance Label indicates the number of operating hours for which the engine has been shown to meet Federal emission requirements.

Category
A = 300 hours
B = 125 hours
C = 50 hours

Engine
Single cylinder four-stroke engine with mixture lubrication

Ignition System
Electronic magneto ignition

Spark plug (resistor type): Bosch USR 7 AC

Electrode gap: 0.5 mm

This spark ignition system meets all requrements of the Canadian Interference-Causing Equipment Regulations ICES-002.

Fuel System
All position diaphragm carburetor with integral fuel pump

Fuel tank capacity: 0.53 L

Weight
dry, without cutting attachment and deflector

Special Accessories

Cutting Attachments
Mowing heads

1. STIHL SuperCut 20-2
2. STIHL AutoCut C 25--2
3. STIHL AutoCut 25-2
4. STIHL TrimCut 31-2
5. STIHL FixCut 25-2
6. STIHL PolyCut 20-3

Metal cutting attachments

7. Grass cutting blade 230-2
8. Grass cutting blade 230-4
9. Grass cutting blade 230-8
10. Grass cutting blade 250-40 Spezial
11. Brush knife 250-3
12. Scratcher tooth circular saw blade 200
13. Chisel tooth circular saw blade 200

Use cutting attachments only as specified in the chapter on "Approved Combinations of Cutting Attachment, Deflector, Handle and Harness".

Special accessories for cutting attachments

• Nylon line for mowing heads 1 to 6
• Prewound spool with nylon line for 1 to 4
• Thermoplastic blades, pack of 12; for 6
• Transport guards for 7 to 13

Sharpening aids for metal cutting attachments

• Flat sharpening files for 7 to 9, 11 and 12
• File holder with round file, for 13
• Saw set, for 13
• STIHL balancer for 7 to 13
• Sharpening templates (metal or cardboard), for 11

Mounting hardware for metal cutting attachments

• Thrust washer
• Rider plate
• Nut

Other special accessories

• Safety glasses
• Shoulder strap
• Full harness
• Combination wrench
• Locking pin
• Carburetor screwdriver
• STIHL gear lubricant for brushcutters
• STIHL filler nozzle for fuels
• Special resin-free lubricating oil

Contact your STIHL dealer for more information on these and other special accessories.

Maintenance and Repairs

Users of this machine may only carry out the maintenance and service work described in this user manual. All other repairs must be carried out by a servicing dealer.

STIHL recommends that you have servicing and repair work carried out exclusively by an authorized STIHL servicing dealer. STIHL dealers are regularly given the opportunity to attend training courses and are supplied with the necessary technical information.

When repairing the machine, only use replacement parts which have been approved by STIHL for this power tool or are technically identical. Only use highquality replacement parts in order to avoid the risk of accidents and damage to the machine.

STIHL recommends the use of original STIHL replacement parts.

Original STIHL parts can be identified by the STIHL part number, the logo and the STIHL parts symbol (the symbol may appear alone on small parts).

If you have any questions regarding your warranty rights and responsibilities, please contact a STIHL customer service representative at www.stihl.ca or you can write to:
STIHL Ltd.,
1515 Sise Road
Box 5666
CA-LONDON ONTARIO; N6A 4L6

Where to make a Claim for Warranty Service
Bring the product to any authorized STIHL servicing dealer and present the signed warranty card.

Maintenance Requirements
The maintenance instructions in this manual are based on the application of the recommended 2-stroke fuel-oil mixture (see also instruction "Fuel"). Deviations from this recommendation regarding quality and mixing ratio of fuel and oil may require shorter maintenance intervals.