STIHL FS 91, 91 R Instruction Manual
English © ANDREAS STIHL AG & Co. KG, 2020 0458-426-0121-A. VA6.A20. 0000007293_011_GB Printed on chlorine-free paper Printing inks contain vegetable oils, paper can be recycled.
English Guide to Using this Manual WARNING 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.
English 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. servicing dealer. Use only high quality tools and accessories in order to avoid the risk of accidents and damage to the machine. The use of noise emitting power tools may be restricted to certain times by national or local regulations. STIHL recommends the use of genuine STIHL tools and accessories.
English STIHL offers a comprehensive range of personal protective clothing and equipment. Transporting by vehicle: Properly secure your power tool to prevent turnover, fuel spillage and damage. Transporting the Power Tool Fueling Gasoline is an extremely flammable fuel. Keep clear of naked flames. Do not spill any fuel – do not smoke. Before Starting Check that your power tool is properly assembled and in good condition – refer to appropriate chapters in the instruction manual.
English – Never attempt to modify the controls or 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 Machine". To reduce the risk of accidents, do not operate your power tool if it is damaged or not properly assembled.
English 15m (50ft) The cutting attachment may catch and fling objects a great distance and cause injury - therefore, do not allow any other persons within a radius of 15 meters of your own position. To reduce the risk of damage to property, also maintain this distance from other objects (vehicles, windows). Even maintaining a distance of 15 meters or more cannot exclude the potential danger.
English Inspect the work area: Stones, pieces of metal or other solid objects may be thrown more than 15 meters and cause personal injury or damage the cutting attachment and property (e.g. parked vehicles, windows). The gearbox gets hot during operation. To reduce the risk of burn injury, do not touch the gearbox housing. Metal cutting attachments must be sharpened regularly as specified.
English 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).
English Deflector must not be used with mowing heads. Shoulder Strap/Harness Mowing Head with Nylon Line The shoulder strap/harness is included with the machine or available as a special accessory. Deflector must not be used with grass cutting blades. Deflector may be used with brush knives. Deflector must not be used with brush knives. Deflector must not be used with shredder blades. Deflector must not be used with circular saw blades. N Use the shoulder strap/harness.
English Check the wear limit marks! Risk of Kickout (Blade Thrust) with Metal Cutting Attachments Grass Cutting Blade 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.
English To reduce the risk of injury it is essential to take the following precautions: 002BA509 KN Use the brushcutter like a scythe (sweep it to the right and left) at ground level when cutting grass and thinning young stands. To cut wild growth and scrub, lower the brush knife down onto the growth to achieve a shredding effect – always keep the cutting attachment below hip level during this process. Exercise extreme caution when using this method of cutting.
English Approved Combinations of Cutting Attachment, Deflector, Handle and Harness Cutting Attachment 1 Deflector, Limit Stop 2 Handle Harness 18 13 19 3 22 24 23 24 23 24 20 4 15 6 7 8 14 21 19 9 10 16 21 11 12 12 20 17 21 25 0000-GXX-1287-A2 5 FS 91, FS 91 R
English Approved Combinations Select correct combination from the table according to the cutting attachment you intend to use. WARNING For safety reasons only the cutting attachments, deflectors, handles and harnesses shown in each row of the table may be used together. No other combinations are permitted because of the risk of accidents.
English Mounting the Bike Handle N Pull out the wing screw – the washer (6) remains on the wing screw. Mounting Bike Handle with Swiveling Handle Support N Separate the clamp moldings – the springs (4 and 5) remain in the lower clamp. The machine is supplied with the swiveling handle support already mounted on the shaft. To mount the handlebar it is necessary to remove the clamp moldings. Securing the Handlebar 8 A N N Hold the lower clamp (1) and upper clamp (2) firmly together.
English Swiveling the Handlebar Mounting the Control Handle Transport position 15 14 12 90° 13 10 15 13 N N N 0000-GXX-0511-A0 7 Take out the screw (9) – the nut (10) remains in the control handle (11). Push the control handle onto the handlebar (7) until the holes (13) line up – the throttle trigger (12) must point towards the gearbox. Insert the screw (9) and tighten it down firmly.
English Mounting the Loop Handle without Barrier Bar Mounting the Loop Handle 2 4 Mounting Loop Handle with Barrier Bar 7 8 7 8 4 3 5 7 1 N 002BA098 KN 1 N Fit the square nuts (1) in the barrier bar (2); the holes must line up. 16 5 6 Place the clamp (3) in the loop handle (4) and position them both against the drive tube (5). N Position the clamp (6) against the drive tube. N Place the barrier bar (2) in position as shown. N Line up the holes.
English Securing the Loop Handle Adjusting the Throttle Cable Fitting the Carrying Ring It may be necessary to correct the adjustment of the throttle cable after assembling the machine or after a prolonged period of operation. Polymer Version Adjust the throttle cable only when the unit is completely and properly assembled. A 1 4 Recommendation: distance (A): about 20 cm (8 in) N Set the throttle trigger to the full throttle position.
English Fitting the Skirt and Blade Mounting the deflector Mounting the Blade WARNING Mounting the Deflector 1 002BA638 KN Risk of injury from thrown objects and contact with the cutting attachment. These parts must be fitted to the deflector (1) when you use a mowing head. Fitting the Skirt 3 N Slide the line limiting blade into the guide on the skirt. N Insert the screw and tighten it down firmly.
English Blocking the Shaft Mounting the Cutting Attachment 3 Placing power tool on the ground 2 N Shut off the engine. N Lay your power tool on its back so that the cutting attachment mounting face is pointing up. Mounting Hardware for Cutting Attachments The mounting hardware supplied depends on the cutting attachment that comes as original equipment with the new machine.
English Fitting Mowing Head with Screw Mounting Removing the Mounting Hardware Remove the mowing head. Keep the instruction leaflet for the mowing head in a safe place. 2 N Block the shaft (4) with the stop pin (2). N Unscrew and remove the mowing head (3) clockwise. Mounting Metal Cutting Attachments 3 4 3 5 0000-GXX-1323-A0 N Block the shaft (5) with the stop pin (1). N Use the combination wrench (2) to loosen and remove the nut (3) clockwise (left-hand thread).
English Check direction of rotation of cutting attachment NOTICE 14 Remove the tool used to block the shaft. Removing the Metal Cutting Attachment 13 3 2 4 9 8 681BA303 KN 6 Cutting attachments 2, 4, 5 and 6 may be mounted either way round – they must be turned over regularly to help avoid one-sided wear. The cutting edges of cutting attachments 1, 3, 7 and 8 must point clockwise. Direction of rotation is indicated by an arrow on the inside of the deflector.
English Fuel Your engine requires a mixture of gasoline and engine oil. WARNING For health reasons, avoid direct skin contact with gasoline and avoid inhaling gasoline vapor. STIHL MotoMix STIHL recommends the use of STIHL MotoMix. This ready-to-use fuel mix contains no benzol or lead, has a high octane rating and ensures that you always use the right mix ratio. STIHL MotoMix uses STIHL HP Ultra two-stroke engine oil for an extra long engine life. MotoMix is not available in all markets.
English Filling Up with Fuel Fueling Fitting the Harness Take care not to spill fuel while fueling and do not overfill the tank. STIHL recommends you use the STIHL filler nozzle for fuel (special accessory). N Preparations Fill up with fuel. Closing the Tank Cap 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".
English Full Harness Balancing the Machine Attaching Machine to Harness 1 3 2 1 1 2 2 1 0000-GXX-0504-A0 N N 1 N Loosen the screw (1). N 002BA660 KN N Slide the carrying ring (2) along the drive tube. N Tighten the screw (1) moderately. N Allow the unit to hang freely. The type and style of the shoulder strap and carabiner depend on the market. N Check the position obtained: 2 Put on the harness (1) and close the locking plate (3).
English Version with Loop Handle 3 1 002BA035 KN Controls B Version with Bike Handle 2 Circular saw blades (B) N should "hover" about 20 cm (8 in) above the ground. 3 When the correct balanced position has been reached: N 1 2 3 Tighten down the screw (1) on the carrying ring firmly. 2 Disconnecting Machine from Harness 0000-GXX-0494-A0 1 2 3 2 1 2 N 2 Throttle trigger lockout Throttle trigger Stop switch with Run and Stop positions.
English 0000-GXX-0479-A0 N Press the manual fuel pump bulb (9) at least five times – even if the bulb is already filled with fuel. Press in the choke knob (8) and turn it to the position that suits the engine temperature: g if the engine is cold < for warm start – also use this position if the engine has been running but is still cold. The choke knob must engage in position.
English As soon as the engine runs Stopping the Engine N Depress the momentary contact stop switch – the engine stops – release the stop switch – it springs back to the run position. Other Hints on Starting Fuel tank run until completely dry N After refueling, press the manual fuel pump bulb at least five times – even if the bulb is already filled with fuel. N Set the choke lever to suit the engine temperature. N Now start the engine. Engine stalls in cold start position g or under acceleration.
English Transporting the Unit The type of transport guard depends on the metal cutting attachment supplied with the machine. Transport guards are available as special accessories.
English 681BA302 KN Circular Saw Blades 681BA301 KN Grass Cutting Blades up to 260 mm Disconnect wire rod from the transport guard. N Swing wire rod outwards. Fit the transport guard on the cutting attachment from below. 1. N 2. N Swing wire rod into position. N Hook wire rod to the transport guard. 681BA275 KN N Disconnect wire rod from the transport guard. 681BA311 KN N 681BA275 KN 1. FS 91, FS 91 R 2. 681BA305 KN 2.
English 681BA276 KN During break-in period N Swing wire rod outwards. N Fit transport guard on saw blade from below, making sure the limit stop is properly seated in the recess. 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.
English The carburetor has been set at the factory to provide an optimum fuel-air mixture under most operating conditions. N If the engine is down on power, difficult to start or runs poorly at idle speed, first check the spark plug. N 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".
English Use resistor type spark plugs with a properly tightened adapter nut. Installing the Spark Plug N Screw the spark plug (3) into the cylinder. N Tighten down the spark plug (3) with the combination wrench. N Press the boot (2) firmly onto the spark plug. N Fit the cover (1) and screw it down firmly.
English For periods of 3 months or longer N Drain and clean the fuel tank in a well ventilated area. N Dispose of fuel properly in accordance with local environmental requirements. N Run the engine until the carburetor is dry – this helps prevent the carburetor diaphragms sticking together. N Remove, clean and inspect the cutting attachment. Coat metal cutting attachments with corrosion inhibitor. N Thoroughly clean the machine. N Clean the air filter.
English Adjusting Nylon Line Maintaining the Mowing Head STIHL SuperCut Placing power tool on the ground Fresh line is advanced automatically if the remaining line is at least 6 cm (2 1/2 in) long. The blade on the deflector trims overlong lines to the correct length. 002BA104 KN STIHL AutoCut N Shut off the engine. N Lay your power tool on its back so that the cutting attachment mounting face is pointing up.
English The mowing head is supplied with illustrated instructions for replacing the blades. Keep the instructions for the mowing head in a safe place. WARNING To reduce the risk of injury, always shut off the engine before installing the blades. N Remove the mowing head. N Replace blades as shown in the illustrated instructions. N Mount the mowing head on the machine.
English Visual inspection (condition, leaks) X Complete machine Clean Replace any damaged parts X Control handle Check operation X Air filter Manual fuel pump (if fitted) Pickup body (filter) in fuel tank X X Visual inspection X X X Check X Have repaired by servicing dealer1) X dealer1) X Have replaced by servicing dealer1) Fuel tank Clean Carburetor Check idle adjustment – the cutting attachment must not rotate X X X X Cooling inlets X Replace after every 100 operating hours
All accessible screws and nuts (not adjustRetighten ing screws) Antivibration elements Visual inspection Cutting attachments Metal cutting attachments Gearbox lubrication Safety labels 1) 2) X Check Have replaced by servicing X X dealer1) X X X X Check tightness X X Sharpen X Replace Check X X X Replenish Replace as required if damaged if problem every 12 months monthly weekly after each refueling stop before starting work The following intervals apply to normal operating condit
English Minimize Wear and Avoid Damage Observing the instructions in this manual helps reduce the risk of unnecessary wear and damage to the power tool. The power tool must be operated, maintained and stored with the due care and attention described in this owner's manual. servicing dealer. STIHL dealers are regularly given the opportunity to attend training courses and are supplied with the necessary technical information. Alterations or modifications to the product not approved by STIHL.
English Main Parts 4 8 9 3 2 10 5 6 1 # 11 7 13 14 21 15 14 16 17 18 12 19 20 15 9 10 8 FS 91, FS 91 R 0000-GXX-0514-A0 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 # Tank cap Carburetor adjusting screw Starter grip Manual fuel pump Cover Muffler Machine support Throttle trigger Stop switch Throttle trigger lockout Bike handle (handlebar) Handle support Wing screw Throttle cable retainer Carrying ring Choke knob Air filter cover Fuel tank Loop handle Barrier bar (country
English 1 2 3 4 5 1 3 2 6 7 8 9 4 1 Drive tube Mowing head Deflector for mowing heads only Line limiting blade Deflector for all mowing attachments Skirt for mowing heads Metal mowing attachment Circular saw blade Limit stop for circular saw blades only 5 6 2 4 1 5 7 1 40 9 002BA644 KN 8 FS 91, FS 91 R
English Weight Specifications Engine Single cylinder four-stroke engine with mixture lubrication Displacement: Bore: Stroke: Engine power to ISO 8893: 28.4 cc 38 mm 25 mm 0.95 kW (1.3 bhp) at 7,000 rpm Idle speed: 2,800 rpm Cut-off speed (rated): 9,500 rpm Max. output shaft speed (cutting attachment): 7,150 rpm Valve clearance Inlet valve: 0.10 mm Exhaust valve: 0.10 mm Ignition System Spark plug (resistor type): Bosch USR 7 AC Electrode gap: 0.
English The CO2value measured in the EU type approval procedure is specified at www.stihl.com/co2. The measured CO2value was determined on a representative engine in accordance with a standardized test procedure under laboratory conditions and does not represent either an explicit or implied guarantee of the performance of a specific engine. The applicable exhaust emission requirements are fulfilled by the intended usage and maintenance described in this instruction manual.
English EC Declaration of Conformity Done at Waiblingen, 28.11.2018 ANDREAS STIHL AG & Co. KG ANDREAS STIHL AG & Co. KG Badstr. 115 D-71336 Waiblingen Germany declare in exclusive responsibility that Category: Make: Model: Serial identification: Displacement: Trimmer STIHL FS 91 FS 91 R 4180 28.
English 44 FS 91, FS 91 R
0458-426-0121-A englisch G www.stihl.
