STIHL FS 55 Brushcutter

Guide to Using this Manual

This manual provides essential information for the safe and effective use of your STIHL FS 55 brushcutter. It is divided into sections covering safety, operation, maintenance, and specifications.

Pictograms

Familiarize yourself with the pictograms used throughout this manual and on the machine itself. These symbols provide important safety and operational information.

• Fuel tank: fuel mixture of gasoline and engine oil
• Operate decompression valve
• Manual fuel pump

Symbols in text

• WARNING: Indicates a risk of accident, personal injury, or serious damage to property.
• NOTICE: Indicates a risk of damage to the machine or its components.

Engineering Improvements

STIHL is committed to continuous product improvement. Design and appearance may be modified periodically. Some changes may not be reflected in this manual.

Safety Precautions and Working Techniques

Operating this high-speed power tool requires strict adherence to safety precautions to minimize the risk of personal injury. Read and understand this manual before operation and keep it for future reference. Failure to comply may result in serious or fatal injury.

Always observe applicable local safety regulations, including those from trade organizations, social insurance institutions, and labor safety authorities.

If you are a new user, seek guidance from your dealer or an experienced user on how to operate the machine.

General Safety Rules

• Minors are not permitted to use the machine, except apprentices aged 16 and above under supervision.
• Keep children, animals, and bystanders at a safe distance.
• When not in use, lay the machine down safely to prevent accidental use or injury.
• The user is responsible for accidents involving third parties or their property.
• Do not lend or rent the power tool without the User Manual. Ensure any user understands the manual's content.
• Be aware of local regulations regarding noise emission limits.
• Operate the machine only when well-rested, in good physical health, and in good mental condition. Consult a doctor if you have any health conditions that could be aggravated by strenuous work.
• Individuals with pacemakers should consult their physician and the pacemaker manufacturer regarding potential interference from the machine's low-intensity electromagnetic field.
• Do not operate the machine if you have consumed alcohol, drugs, or medications that impair reaction time.

Intended Use

Use the power tool only for cutting grass, wild growth, shrubs, scrub, bushes, small diameter trees, and similar materials, depending on the fitted cutting attachment. Do not use the machine for any other purpose to avoid accidents.

Cutting Attachments and Accessories

Only use cutting attachments and accessories explicitly approved by STIHL for this model or that are technically identical. Use only high-quality parts and accessories to prevent accidents and damage.

Clothing and Equipment

• Wear appropriate protective clothing and equipment that allows complete freedom of movement.
• Wear close-fitting clothes, such as a boiler suit; avoid loose jackets.
• Do not wear clothing that could get caught in moving parts. Avoid scarves, neckties, and jewelry. Tie long hair above your shoulders.
• Wear safety boots with steel toe caps and non-slip soles. Sturdy shoes with non-slip soles are acceptable only when using mowing heads.
• Wear close-fitting safety glasses conforming to European Standard EN 166. Ensure a snug fit.
• Wear face protection that fits well. Face protection alone does not protect the eyes.
• Wear personal sound protection, such as ear defenders.
• Wear a safety hard hat for thinning operations, working in high scrub, or when there is a risk of head injury from falling objects.
• Wear sturdy protective gloves made of a resistant material (e.g., leather).

STIHL offers a comprehensive range of personal protective equipment.

Transporting the Machine

• Always stop the engine before transporting.
• Carry the machine balanced on the harness or shaft.
• Fit the transport guard on the cutting attachment, even for short distances, to reduce the risk of cut injuries.
• Avoid touching hot parts of the machine and gearbox to prevent burns.
• When transporting in a vehicle, secure the machine properly to prevent turnover, damage, and fuel spillage.

Refueling

• Gasoline is highly flammable. Keep away from open flames and do not smoke while refueling.
• Always shut off the engine before refueling.
• Do not refuel a hot engine to prevent fuel spillage and fire.
• Open the fuel cap carefully to release pressure slowly and avoid fuel spillage.
• Refuel only in a well-ventilated area. Clean up any spilled fuel immediately. If fuel splashes on clothing, change clothes immediately.
• Close the fuel cap tightly after refueling.
• This helps prevent the fuel cap from loosening due to vibrations and spilling fuel.
• Check for leaks. Do not start the engine if there is a fuel leak, as this could cause serious or fatal burns.

Before Starting

• Ensure the power tool is properly assembled and in good condition.
• Check the fuel system for leaks, including the fuel cap, hose connections, and manual fuel pump. Do not start the engine if a leak is detected.
• Have the machine serviced by a dealer before use if necessary.
• Use only approved combinations of cutting attachment, deflector, handle, and harness. Ensure all parts are properly assembled and secured.
• Verify that the slide control/stop switch moves freely to STOP or 0.
• Check that the throttle trigger lockout and throttle trigger move freely and that the throttle trigger returns to the idle position automatically.
• Ensure the spark plug boot is secure, as a loose boot can cause sparking that ignites combustible fumes.
• Ensure the cutting attachment or interchangeable attachment is correctly fitted, secure, and in perfect condition.
• Check safety devices (deflector, rider plate) for damage or wear. Replace damaged parts immediately. Do not operate with a damaged deflector or worn rider plate.
• Never attempt to modify controls or safety devices.

Starting the Engine

Start the engine at least 3 meters (10 ft) from the fueling spot, in an open area.

• Place the unit on firm ground in an open area, ensuring good balance and secure footing.
• Hold the unit securely. Ensure the cutting attachment is clear of the ground and obstructions, as it may start rotating when the engine starts.
• Ensure no one is within 15 meters (50 ft) of the machine during starting.
• Avoid contact with the cutting attachment.
• Do not drop-start the power tool. Start the engine as described in the manual. The cutting attachment may rotate briefly after releasing the throttle trigger (coasting effect).
• Check engine idling: the cutting attachment must remain stationary when the engine idles with the throttle trigger released.
• Keep combustible materials away from hot exhaust gases and muffler surfaces.

Holding and Guiding the Machine

• Always hold the unit firmly with both hands on the handles.
• Maintain good balance and secure footing.
• Keep handles dry and clean for safe control.
• Adjust harness and handles to suit your height and reach.
• Do not operate a damaged or improperly assembled power tool.
• Practice setting down the machine quickly for emergencies.

While Working

• Maintain good balance and secure footing.
• In an emergency, switch off the engine immediately by moving the slide control/stop switch to STOP or 0.
• Maintain a 15-meter (50 ft) radius around the workplace to prevent injury from ejected objects. This distance also applies to vehicles and windows to prevent property damage.
• Check that the engine idles properly, so the cutting tool does not rotate after releasing the throttle trigger.
• Correct the idle speed setting regularly. If the cutting attachment still rotates at idle speed, have it serviced by a dealer.
• Take special care in slippery conditions (damp, snow, ice, slopes, uneven ground).
• Watch out for obstacles like tree stumps and roots.
• Work only on the ground, not on ladders or elevated platforms.
• Be alert and cautious when wearing hearing protection, as your ability to hear warnings is reduced.
• Take breaks when tired to prevent accidents.
• Work calmly and carefully in daylight with good visibility. Do not endanger others.
• WARNING: The engine produces toxic exhaust gas. Never run the engine indoors or in poorly ventilated areas, even with a catalytic converter. Ensure proper ventilation when working in confined spaces to avoid inhaling toxic fumes.
• Stop work immediately if you experience nausea, headaches, impaired vision, impaired hearing, dizziness, or impaired concentration, as these may indicate high exhaust gas concentration.
• Operate the tool to minimize noise and emissions. Accelerate the engine only when necessary.
• To reduce the risk of fire, do not smoke while operating or near the power tool.
• Wear respiratory protection if exposed to dust, fumes, or smoke.
• If the power tool is subjected to unusually high loads, check its condition before further use.
• Ensure the fuel system has no leaks and safety equipment is operative. Never use a power tool that is unsafe.
• Do not operate the tool in the starting throttle position.
• WARNING: Never operate the unit without the proper deflector for the cutting attachment.
• Check the work site for objects that could be ejected.
• Be careful on difficult or densely grown terrain.
• When mowing in high shrubbery or hedges, hold the cutting tool at least 15 cm (6 in) from the ground to avoid harming animals.
• Always shut off the engine before leaving the unit unattended.
• Periodically inspect the cutting attachment for damage or wear. Stop the engine, secure the machine, and allow the attachment to stop before inspection. Check for cracks and secure fitting. Replace damaged or blunt cutting attachments immediately.
• Clean grass and plant residue from the cutting attachment mounting and deflector.
• Shut off the engine before replacing the cutting attachment.
• WARNING: The gearbox gets hot during operation. Avoid touching it to prevent burns.

Using Mowing Heads

Nylon line provides a soft cut for edging and trimming, reducing the risk of damaging tree bark.

• Follow the instructions in the mowing head's leaflet for refilling with nylon line.
• WARNING: Never use wire or metal-reinforced line instead of nylon line.

STIHL PolyCut Mowing Head with Polymer Blades

Use for mowing unobstructed edges of meadows.

• Check wear limit marks. If worn through, replace the mowing head to avoid injury from thrown parts.
• Follow maintenance instructions for the PolyCut mowing head.
• The PolyCut can also be equipped with mowing line instead of polymer blades.
• Refer to the mowing head's instruction leaflets for equipping with blades or line.

Risk of Kickout (Blade Thrust) with Metal Cutting Attachments

WARNING: Kickout can occur when a rotating blade contacts a solid object (tree trunk, branch, stump, rock). The machine may be thrown to the right or rear.

• The risk of kickout is greatest when the black area of the cutting attachment contacts a solid object.

Approved Combinations of Cutting Attachment, Deflector, Handle and Harness

For safety reasons, only combine cutting attachments, deflectors, handles, and harnesses listed in the same line of the table. Other combinations are not permitted due to accident risk.

Cutting Attachments

• Mowing Heads: STIHL SuperCut 20-2, STIHL AutoCut C 25-2, STIHL AutoCut 25-2 / AutoCut 27-2, STIHL AutoCut C 26-2, STIHL TrimCut 31-2, STIHL TrimCut 32-2, STIHL DuroCut 20-2, STIHL PolyCut 20-3, STIHL PolyCut 28-2
• Metal Cutting Tools: Grass cutting blade 230-2 (230 mm dia.), Grass cutting blade 230-4 (230 mm dia.), Grass cutting blade 230-8 (230 mm dia.)

WARNING: Do not use grass cutting blades made of materials other than metal.

Deflectors

• Deflector for mowing heads
• Deflector for metal cutting attachments

Handles

• Loop handle
• Loop handle with barrier bar
• Bike handle

Shoulder Straps

• Shoulder strap can be used
• Shoulder strap must be used

Grass Cutting Blade

Use for grass and weeds only. Sweep in an arc like a scythe.

WARNING: Improper use may damage the grass cutting blade and cause injury from thrown parts. Resharpen the blade when dulled.

Mounting the Bike Handle

Mounting the Handlebar

• Position the clamp and handlebar support on the shaft.
• Place the handlebar in the support, ensuring the rubber handle is on the left.
• Place the clamp on the handlebar support.
• Insert and tighten screws through the holes into the clamp.
• Fasten the handlebar at a distance of approximately 15 cm (6 in) ahead of the engine housing on the shaft.
• Align the handlebar and tighten the screws firmly.

Mounting the Control Handle

• Unscrew the bolt with a combination wrench or hex key wrench.
• Push the control handle with the throttle trigger facing the gearbox onto the handlebar until the holes align.
• Insert and tighten the screw.

Fastening the Throttle Cable

NOTICE: Do not kink the throttle cable or lay it in tight radii. Ensure the throttle trigger moves freely.

• Position the throttle cable retainer and the throttle cable on the shaft.
• Squeeze the throttle cable retainer; it will engage with an audible click.

Mounting the Loop Handle

Mounting Loop Handle with Barrier Bar

• Fit square nuts into the barrier bar; align holes.
• Place the barrier bar in position.
• Line up the holes.
• Insert screws and screw them into the barrier bar.
• Proceed to "Securing the Loop Handle".

Mounting the Loop Handle without Barrier Bar

• Place the clamp in the loop handle and position them against the drive tube.
• Position the clamp against the drive tube.
• Line up the holes.
• Fit washers on the screws, insert screws, fit square nuts, and screw them down.
• Proceed to "Securing the Loop Handle".

Securing the Loop Handle

The loop handle can be adjusted for height and reach by changing distance (A). Recommendation: distance (A) about 20 cm (8 in).

• Slide the handle to the required position.
• Line up the loop handle.
• Tighten screws until the loop handle cannot be rotated. If no barrier bar is fitted, lock the nuts.
• The sleeve (not on all models) must be between the loop handle and the control handle.

Fitting the Carrying Ring

The carrying ring is standard or available as an accessory.

• Position the clamp against the drive tube with the tapped hole on the left.
• Squeeze the clamp ends together.
• Insert the M6x14 screw.
• Line up the carrying ring.
• Tighten the screw firmly.

Mounting the Deflector

Use the right deflector

WARNING: Deflector (1) is for mowing heads only. Deflector (2) is for grass cutting blades only.

Mounting the deflector

Deflectors (1) and (2) mount to the gearbox similarly.

• Position the deflector against the gearbox so the lug engages the recess.
• Insert and tighten the screw firmly.

Mounting the Cutting Attachment

Placing power tool on the ground

Shut off the engine. Lay the power tool on its back with the cutting attachment mounting face pointing up.

Mounting Hardware for Cutting Attachments

Mounting hardware depends on the cutting attachment supplied with the machine. Mowing heads and metal cutting attachments may be mounted.

Blocking the Shaft

The output shaft must be blocked with the stop pin or screwdriver to mount or remove cutting attachments.

• Insert the stop pin or screwdriver into the gearbox hole as far as possible and apply slight pressure.
• Rotate the shaft, nut, or cutting attachment until the stop pin blocks the shaft.

Removing the Mounting Hardware

• Block the shaft.
• Use the combination wrench to loosen and remove the nut (left-hand thread).
• Take off the thrust washer. Do not remove the thrust plate.

Mounting the Cutting Attachment

WARNING: Use a deflector that matches the cutting attachment.

Fitting the mowing head with screw mounting

Keep the supplement sheet for the mowing head in a safe place.

Removing the Mowing Head

• Retain the shaft.
• Turn the mowing head clockwise.

Mounting Metal Cutting Attachment

WARNING: Wear protective gloves to reduce the risk of direct contact with sharp cutting edges. Mount only metal cutting attachments.

Securing the cutting attachment

• Fit the thrust washer (convex side up).
• Fit the rider plate.
• Block the shaft.
• Use the combination wrench to screw the mounting nut onto the output shaft counterclockwise and tighten firmly.
• WARNING: If the mounting nut becomes loose, fit a new one.

NOTICE: Remove the tool used to block the shaft.

Removing the Metal Cutting Attachment

WARNING: Wear protective gloves to reduce the risk of direct contact with sharp cutting edges.

• Block the shaft.
• Unscrew the mounting nut clockwise.
• Remove the cutting attachment and its mounting hardware, but do not remove the thrust plate.

Fuel

The engine requires a mixture of gasoline and engine oil.

WARNING: Avoid direct skin contact with fuel and breathing in gasoline fumes.

STIHL MotoMix

STIHL recommends STIHL MotoMix, a pre-blended fuel free of benzene and lead, with a high octane rating and the correct mixing ratio. STIHL HP Ultra two-stroke engine oil is recommended for optimal engine life. MotoMix may not be available in all markets.

Mixing fuel

NOTICE: Unsuitable fuels or incorrect mixing ratios can cause severe engine damage.

• Gasoline: Use high-quality gasoline with an octane rating of at least 90 ROC. Gasoline with an alcohol component exceeding 10% may impair performance in engines with manually adjustable carburetors. Engines with M-Tronic can use gasoline with up to 27% alcohol (E27).
• Engine oil: Use only STIHL two-stroke engine oil or other high-performance engine oil classified as JASO FB, JASO FC, JASO FD, ISO-L-EGB, ISO-L-EGC, or ISO-L-EGD.
• Mixing ratio: STIHL two-stroke engine oil 1:50 (1 part oil + 50 parts gasoline).
• Examples: Quantities for 1L to 25L of gasoline are provided in a table.
• Pour oil into an approved safety fuel canister first, then add gasoline and mix thoroughly.

Storing fuel mixture

Store in approved safety fuel canisters in a dry, cool, and secure place protected from light. Fuel mixture deteriorates with age; mix only as needed. Do not store for longer than 30 days, as it can become unusable quickly if exposed to light, sunlight, or temperature fluctuations. STIHL MotoMix can be stored for up to 5 years.

WARNING: Pressure may build up in the canister; open carefully. Shake the canister before refueling.

Clean the fuel tank and canister regularly.

Dispose of residual fuel and cleaning liquid according to regulations.

Fueling

• Before fueling, clean the filler cap and surrounding area to prevent dirt from entering the tank.
• Position the machine so the filler cap faces up.
• Open the filler cap.
• Avoid spilling fuel and do not overfill the tank. STIHL recommends using the STIHL filler nozzle.
• After fueling, tighten the filler cap securely by hand.

Fitting the Harness

Harness type and style vary by market.

Shoulder strap

• Put on the shoulder strap.
• Adjust the strap length so the carabiner is about a hand's width below your right hip.
• Balance the machine.

Full Harness

• Put on the harness and close the locking plate.
• Adjust the strap length so the carabiner is about a hand's width below your right hip.
• Balance the machine (see "Balancing the Machine").

Balancing the Machine

The carrying ring is integrated in the control handle on loop-handled units. Loop-handled units do not need to be balanced.

Attaching the unit to the harness

• Attach the carabiner to the carrying ring on the drive tube.
• Loosen the screw.

Floating position

Mowing heads and grass cutting blades should just touch the ground.

• Adjust the floating position by moving the carrying ring up or down the drive tube. Tighten the screw moderately, let go of the unit, wait for balance, and check the floating position.
• Tighten the screw on the carrying ring firmly once the correct floating position is reached.

Detaching the unit from the harness

• Press down the bar on the carabiner and pull the carrying ring out of the carabiner.

Starting / Stopping the Engine

Version with bike handle

Controls

• Throttle trigger lockout
• Throttle trigger
• Slide control
• START position: Ignition is switched on.
• Normal run position: Engine is running.
• STOP position: Engine is off, ignition is switched off.

Positions of slide control

7 - stop symbol and arrow. To stop the engine, push the slide control in the direction of the arrow to STOP-0.

Starting

• Press down the trigger lockout lever and squeeze the throttle trigger.
• Move the slide control to START.
• Release the throttle trigger, slide control, and trigger lockout in that order. This is the starting throttle position.
• Refer to "All versions".

Version with loop handle

Controls

• Stop switch
• Throttle trigger lockout
• Throttle trigger
• Tongue of throttle trigger
• Catch

Positions of stop switch

• I - normal run position: Engine can start or is running.
• 0 - Stop: Engine off, ignition is switched off.

Starting

• Move the stop switch to I.
• Press down the throttle trigger lockout and hold it.
• Squeeze the throttle trigger until the catch on the tongue engages.
• Release the throttle trigger, tongue, and trigger lockout in that order. This is the starting throttle position.
• Refer to "All versions".

All models

• Place the unit on the ground, resting securely on the engine support and deflector.
• If fitted, remove the transport guard from the cutting attachment.
• Ensure the cutting attachment does not touch the ground or other obstacles.
• Ensure firm footing (standing, stooping, or kneeling).
• Hold the unit firmly with your left hand and press down. Do not touch the throttle trigger, lockout lever, or stop switch.

NOTICE: Do not stand or kneel on the drive tube.

Cranking

• Hold the starter grip with your right hand.
• Version without ErgoStart: Pull the starter grip slowly until it engages, then pull briskly.
• Version with ErgoStart: Pull the starter grip slowly until it engages, then pull slowly and steadily.

NOTICE: Do not pull the starter rope all the way out; it might break.

• Both versions: Do not let the starter grip snap back. Guide it slowly back into the housing. Continue cranking.

When engine begins to fire

• After no more than five pulls, move the choke lever to the normal run position. Continue cranking.

As soon as the engine runs

• Version with bike handle: Blip the throttle trigger; the engine will settle to idle speed.
• Version with loop handle: Squeeze the throttle trigger to disengage the tongue; the engine will settle to idle speed.

Your machine is now ready for operation.

WARNING: Ensure the carburetor is correctly adjusted. The cutting attachment must not rotate when the engine is idling.

Stopping the Engine

• Move the slide control to STOP-0 or the stop switch to STOP/0.

If engine does not start

• Choke lever: If the choke lever was not moved quickly enough after the engine began to fire, the combustion chamber may be flooded.
• Set the slide control, trigger 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 or stop switch to STOP/0.
• Remove and dry the spark plug.
• Crank the engine several times to clear the combustion chamber.
• Refit the spark plug.
• Move the slide control or stop switch to I/I.
• Set the choke lever to the appropriate position for the engine temperature.
• Start the engine.

Fuel tank run until completely dry

• After refueling, press the manual fuel pump bulb at least five times.
• Set the choke lever according to engine temperature.
• Start the engine.

Transporting the Unit

Using transport guard

The type of transport guard depends on the metal cutting attachment. Transport guards are available as special accessories.

230 mm Grass Cutting Blades

Operating Instructions

During break-in period

Do not run the machine at high revs (full throttle off load) for the first three tank fillings to avoid unnecessary high loads. Frictional resistances in the engine are greater during this period. The engine develops maximum power after about 5 to 15 tank fillings.

During Operation

After prolonged full throttle operation, allow the engine to run at idle speed for a short time to dissipate engine heat via cooling air. This protects engine-mounted components from thermal overload.

After Finishing Work

For short-term storage, wait for the engine to cool down. Empty the fuel tank and store the machine in a dry place away from ignition sources. For longer periods, see "Storing the Machine".

Cleaning the Air Filter

If there is a noticeable loss of engine power

• Set the choke lever to I.
• Press the tab and swing the filter cover down.
• Clean away loose dirt from around the filter.

Adjusting the Carburetor

General Information

The carburetor is factory-set for optimal fuel-air mixture under most operating conditions.

Preparations

• Shut off the engine.
• Mount the cutting attachment.
• Check and clean or replace the air filter if necessary.
• Check the spark arresting screen in the muffler and clean or replace if necessary.

Different Standard Settings

Different carburetors are installed at the factory. A different standard setting is necessary for each.

Identifying the Carburetor

Use the following illustrations to identify your carburetor and adjust it as described.

• Carburetor 1: 2-MIX carburetor with limiter caps on high speed (H) and low speed (L) screws, marked "2-MIX".
• Carburetor 2: Carburetor without limiter caps on high speed (H) and low speed (L) screws.

Standard Setting on Carburetor 1

• Turn high speed screw (H) counterclockwise as far as stop (no more than 3/4 turn).
• Turn the low speed screw (L) carefully clockwise until it seats, then back it off 3/4 turn.

Standard Setting on Carburetor 2

• Turn the high speed screw (H) carefully clockwise until it seats, then turn it back 2 full turns.
• Turn the low speed screw (L) carefully clockwise until it seats, then turn it back 1 1/2 turns.

Adjusting Idle Speed

• Carry out the standard setting.
• Start and warm up the engine.
• Engine stops while idling: Turn the idle speed screw (LA) clockwise until the engine runs smoothly and the cutting attachment does not rotate.
• Cutting attachment rotates when engine is idling: Turn the idle speed screw (LA) counterclockwise until the cutting attachment stops moving, then turn the screw another 1/2 to 1 full turn in the same direction.

WARNING: If the cutting attachment continues to rotate when the engine is idling, have your machine checked and repaired by your servicing dealer.

Erratic idling behavior, poor acceleration (idle setting too lean)

• Carburetor 1: Turn the low speed screw (L) counterclockwise until the engine runs smoothly and accelerates satisfactorily.
• Carburetor 2: Rotate the low speed screw (L) about 1/4 turn counterclockwise until the engine runs smoothly and accelerates satisfactorily.

Erratic idling behavior (idle setting too rich)

• Carburetor 1: Turn the low speed screw (L) clockwise until the engine runs smoothly and accelerates satisfactorily.
• Carburetor 2: Rotate the low speed screw (L) about 1/4 turn clockwise until the engine runs smoothly and accelerates satisfactorily.

It is usually necessary to change the idle speed screw (LA) setting after correcting the low speed screw (L).

Fine Tuning for Operation at High Altitude

A slight correction may be necessary if the engine does not run satisfactorily:

• Carburetor 1: Carry out standard setting, warm up engine, turn high speed screw (H) slightly clockwise (leaner) – no further than stop.
• Carburetor 2: Carry out standard setting, warm up engine, turn high speed screw (H) slightly clockwise (leaner) – no more than 3/4 turn.

NOTICE: After returning from high altitude, reset the carburetor to the standard setting. If the setting is too lean, there is a risk of engine damage due to insufficient lubrication and overheating.

Spark Plug

If the engine is down on power, difficult to start, or runs poorly at idle, check the spark plug.

• Replace the spark plug after about 100 operating hours or sooner if electrodes are eroded. Use only suppressed spark plugs approved by STIHL.

Removing the Spark Plug

• Move the stop switch to 0.
• Pull off the spark plug boot.
• Unscrew the spark plug.

Checking the Spark Plug

• Clean dirty spark plugs.
• Check electrode gap (A) and readjust if necessary.
• Rectify problems that caused fouling (e.g., too much oil in fuel mix, dirty air filter, unfavorable running conditions).

WARNING: Arcing may occur if the adapter nut is loose or missing, potentially causing fire or explosion in combustible atmospheres. Use resistor type spark plugs with a properly tightened adapter nut.

Installing the spark plug

• Screw in the spark plug, fit the boot, and press it down firmly.

Engine Running Behavior

If engine running behavior is unsatisfactory despite a clean air filter and properly adjusted carburetor, the cause may be the muffler. Have the muffler checked for contamination by your servicing dealer.

STIHL recommends servicing and repair work be carried out exclusively by an authorized STIHL servicing dealer.

Storing the Machine

If the machine is out of use for about 30 days or longer:

• Drain and clean the fuel tank in a well-ventilated area. Dispose of fuel properly.
• If a manual fuel pump is fitted, press it at least 5 times.
• Start the engine and run it at idle speed until it stops.
• Remove, clean, and inspect the cutting attachment. Coat metal cutting attachments with corrosion inhibitor.
• Thoroughly clean the machine, paying attention to cylinder fins and air filter.

Sharpening Metal Cutting Blades

• Use a sharpening file to sharpen dull cutting attachments. For more serious wear or nicks, use a grinder or have the work done by a STIHL servicing dealer.
• Sharpen frequently, removing as little metal as possible (two or three strokes of the file are usually sufficient).
• Resharpen teeth uniformly; do not alter the contour of the parent blade.
• Keep cutting attachment packaging for future sharpening instructions.

Balancing

After resharpening about 5 times, check the cutting attachment for balance on a STIHL balancer or have it checked by a dealer.

Maintaining the Mowing Head

Placing power tool on the ground

Shut off the engine. Lay the power tool on its back with the cutting attachment mounting face up.

Replacing Nylon Line

Always check the mowing head for signs of wear before replacing nylon line.

WARNING: If there are signs of serious wear, replace the complete mowing head.

• Refer to the mowing head's illustrated instructions for replacing the line. Keep these instructions in a safe place.
• If necessary, remove the mowing head.

Adjusting Nylon Line

• STIHL SuperCut: Fresh line advances automatically if at least 6 cm (2 1/2 in) of line remains. The blade on the deflector trims overlong lines.
• STIHL AutoCut: With the engine running, hold the mowing head above the grass surface and tap it on the ground once. Fresh line advances and is trimmed. Repeat as needed. Avoid tapping too often, as the line limiting blade may cut off unused line. Line feed operates only if both lines are at least 2.5 cm (1 in) long.
• STIHL TrimCut:WARNING: Shut off the engine before adjusting nylon line by hand. Pull the spool up, rotate it 1/6 turn counterclockwise until it engages, and let it spring back. Pull the ends of the lines outward. Repeat as necessary. Rotating the spool advances about 4 cm (1 1/2 in) of fresh line.

Replacing Nylon Line

• STIHL PolyCut: Precut lengths of nylon line can be fitted instead of cutting blades.
• STIHL DuroCut, STIHL PolyCut:WARNING: Shut off the engine before refilling the mowing head. Fit precut lengths of nylon line as described in the supplied instructions.

Replacing Cutting Blades

• STIHL PolyCut: Always check the mowing head for signs of wear before installing new cutting blades.
• WARNING: If there are signs of serious wear, replace the complete mowing head.
• WARNING: Shut off the engine before installing blades. Remove the mowing head. Replace blades as shown in the illustrated instructions. Mount the mowing head on the machine.

Inspections and Maintenance by Dealer

Maintenance Work

STIHL recommends that servicing and repair work be carried out exclusively by an authorized STIHL servicing dealer.

Fuel Pickup Body in Tank

Have the pickup body in the fuel tank replaced every year.

Maintenance and Care

The following intervals apply to normal operating conditions. Shorten intervals if working in difficult conditions (e.g., dusty areas).

¹ STIHL recommends an authorized STIHL servicing dealer.
² not in all versions, market-specific

Minimize Wear and Avoid Damage

Following the instructions in this manual helps reduce unnecessary wear and damage to the power tool. Operate, maintain, and store the tool with due care and attention as described.

The user is responsible for damage caused by non-observance of safety precautions, operating, and maintenance instructions. This includes:

• Alterations or modifications not approved by STIHL.
• Using unapproved or unsuitable tools or accessories.
• Using the product for purposes for which it was not designed.
• Using the product for sports or competitive events.
• Consequential damage from continuing to use defective components.

Maintenance Work

Perform operations described in the "Maintenance Chart" regularly. If unable to perform maintenance, have it done by a servicing dealer.

STIHL recommends servicing and repair work be carried out exclusively by authorized STIHL servicing dealers.

Failure to perform maintenance as specified may result in damage, including:

• Engine damage due to neglect or deficient maintenance (e.g., air/fuel filters, carburetor adjustment, cooling air inlets).
• Corrosion and consequential damage from improper storage.
• Machine damage from using poor quality replacement parts.

Parts Subject to Wear and Tear

Some parts are subject to normal wear and tear and require timely replacement. These include:

• Cutting attachments (all types)
• Mounting hardware for cutting attachments
• Deflectors for cutting attachments
• Clutch
• Filters (air, fuel)
• Rewind starter
• Spark plug

Main Parts

Diagrams illustrating the main parts of the brushcutter are provided, with numbered components corresponding to a list:

• 1 Manual fuel pump
• 2 Carburetor adjusting screws
• 3 Spark plug boot
• 4 Starter grip
• 5 Muffler (with spark arrestor)
• 6 Throttle trigger
• 7 Slide control
• 8 Throttle trigger lockout
• 9 Bike handle (handlebar)
• 10 Handle support
• 11 Carrying ring
• 12 Throttle cable retainer
• 13 Choke lever
• 14 Air filter cover
• 15 Tank cap

Specifications

Engine

• FS 55: Single-cylinder two-stroke engine. Displacement: 27.2cm³. Cylinder bore: 34 mm. Piston stroke: 30 mm. Engine power to ISO 8893: 0.75 kW (1.0 hp) at 7000 1/min. Idle speed: 2800 rpm. Cut-off speed: 9500 rpm. Max. output shaft speed: 7700 rpm.
• FS 55 2-MIX: Displacement: 27.2cm³. Cylinder bore: 34 mm. Piston stroke: 30 mm. Engine power to ISO 8893: 0.75 kW (1.0 hp) at 8500 1/min. Idle speed: 2800 rpm. Cut-off speed: 10000 rpm. Max. output shaft speed: 8100 rpm.

Ignition system

Electronic magneto ignition. Suppressed spark plug: Bosch WSR 6 F, NGK BPMR 7 A, STIHL ZK C 14. Electrode gap: 0.5 mm.

Fuel system

All-position diaphragm carburetor with integral fuel pump. Fuel tank capacity: 330 cm³ (0.33 l).

Weight

Dry, without cutting attachment and deflector:

• FS 55: 5.0 kg
• FS 55 2-MIX: 5.1 kg
• FS 55 C (with ErgoStart): 5.2 kg
• FS 55 R: 4.8 kg
• FS 55 R 2-MIX: 4.9 kg
• FS 55 RC (with ErgoStart): 5.0 kg

Sound and Vibration Levels

Idle speed and nominal maximum speed are considered for sound and vibration levels. For details on Vibration Directive 2002/44/EC, see www.stihl.com/vib.

• Sound pressure level L_pA (ISO 22868):
• With mowing head, FS 55 with bike handle: 95 dB(A)
• FS 55 R: 95 dB(A)
• With metal mowing tool, FS 55 with bike handle: 94 dB(A)
• FS 55 R with barrier bar: 94 dB(A)
• Sound power level L_wA (ISO 22868):
• With mowing head, FS 55 with bike handle: 108 dB(A)
• FS 55 R: 108 dB(A)
• With metal mowing tool, FS 55 with bike handle: 107 dB(A)
• FS 55 R with barrier bar: 107 dB(A)
• Vibration level a_hv,eq (ISO 22867):
• With mowing head, FS 55 with bike handle: 5.5 m/s²
• FS 55 R: 8.5 m/s²
• With metal mowing tool, FS 55 with bike handle: 6.8 m/s²
• FS 55 R with barrier bar: 8.0 m/s²

K-factor (Directive 2006/42/EC): 2.0 dB(A) for sound, 2.0 m/s² for vibration.

REACH

REACH is an EC regulation for Registration, Evaluation, Authorization, and Restriction of Chemical substances. For compliance information, see www.stihl.com/reach.

Exhaust Emissions

CO2 value measured in EU type approval procedure is specified at www.stihl.com/co2. This value is determined under laboratory conditions and does not guarantee performance of a specific engine. Exhaust emission requirements are fulfilled by intended usage and maintenance described in this manual. The operating license is void if the engine is modified.

Maintenance and Repairs

Users may only perform maintenance and service work described in this manual. All other repairs must be carried out by a servicing dealer.

STIHL recommends servicing and repair work be carried out exclusively by authorized STIHL servicing dealers.

When repairing, use only STIHL-approved or technically identical replacement parts. Use high-quality replacement parts to avoid accidents and damage.

Original STIHL parts can be identified by the STIHL part number, STIHL logo, and STIHL parts symbol 5.

Disposal

Contact local authorities or your STIHL servicing dealer for disposal information. Improper disposal can harm health and the environment.

Take STIHL products and packaging to a suitable collection point for recycling. Do not dispose of with domestic waste.

EC Declaration of Conformity

ANDREAS STIHL AG & Co. KG, Badstr. 115, D-71336 Waiblingen, Germany, declares under sole responsibility that the Brushcutter (Make: STIHL, Series: FS 55, FS 55 C, FS 55 C-E, FS 55 R, FS 55 RC, FS 55 RC-E) conforms to relevant provisions of Directives 2011/65/EU, 2006/42/EC, 2014/30/EU and 2000/14/EC. Manufactured in compliance with standards EN ISO 11806-1, EN 55012, EN 61000-6-1.

Measured sound power level: 108 dB(A). Guaranteed sound power level: 110 dB(A).

Technical documents deposited at: ANDREAS STIHL AG & Co. KG, Produktzulassung (Product Licensing). Year of manufacture and serial number are applied to the product.

Done at Waiblingen, 03.02.2020

ANDREAS STIHL AG & Co. KG

Dr. Jürgen Hoffmann
Director Product Certification & Regulatory Affairs

CE