Instruction Manual
Table Of Contents
- STIHL FS 91, 91 R
- 1 Guide to Using this Manual
- 2 Safety Precautions and Working Techniques
- 2.1 Clothing and equipment
- 2.2 Transporting the machine
- 2.3 Refueling
- 2.4 Before starting
- 2.5 Starting the engine
- 2.6 Holding and guiding the machine
- 2.7 While working
- 2.8 Using mowing heads
- 2.9 When using metal cutting attachments
- 2.10 Vibrations
- 2.11 Maintenance and Repairs
- 2.12 Symbols on Deflectors
- 2.13 Shoulder Strap/Harness
- 2.14 Mowing Head with Nylon Line
- 2.15 STIHL Polycut Mowing Head with Polymer Blades
- 2.16 Risk of Kickout (Blade Thrust) with Metal Cutting Attachments
- 2.17 Grass Cutting Blade
- 2.18 Brush Knife
- 2.19 Circular Saw Blade
- 3 Approved Combinations of Cutting Attachment, Deflector, Handle and Harness
- 4 Approved Power Tool Attachments
- 5 Mounting the Bike Handle
- 6 Mounting the Loop Handle
- 7 Adjusting the Throttle Cable
- 8 Fitting the Carrying Ring
- 9 Mounting the deflector
- 10 Mounting the Cutting Attachment
- 10.1 Placing power tool on the ground
- 10.2 Mounting Hardware for Cutting Attachments
- 10.3 Blocking the Shaft
- 10.4 Removing the Mounting Hardware
- 10.5 Mounting the Cutting Attachment
- 10.6 Fitting Mowing Head with Screw Mounting
- 10.7 Remove the mowing head.
- 10.8 Mounting Metal Cutting Attachments
- 10.9 Removing the Metal Cutting Attachment
- 11 Fuel
- 12 Fueling
- 13 Fitting the Harness
- 14 Balancing the Machine
- 15 Starting / Stopping the Engine
- 16 Transporting the Unit
- 17 Operating Instructions
- 18 Replacing the Air Filter
- 19 Adjusting the Carburetor
- 20 Spark Arresting Screen in Muffler
- 21 Spark Plug
- 22 Engine Running Behavior
- 23 Lubricating the Gearbox
- 24 Storing the Machine
- 25 Sharpening Metal Cutting Blades
- 26 Maintaining the Mowing Head
- 27 Maintenance and Care
- 28 Minimize Wear and Avoid Damage
- 29 Main Parts
- 30 Specifications
- 31 Maintenance and Repairs
- 32 Disposal
- 33 EC Declaration of Conformity
► Remove cutting attachment and its mounting
hardware from the gearbox – but do not
remove the thrust plate (9).
11 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.
11.1 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.
11.2 Mixing Fuel
NOTICE
Unsuitable fuels or lubricants or mix ratios other
than those specified may result in serious dam‐
age to the engine. Poor quality gasoline or
engine oil may damage the engine, sealing rings,
hoses and the fuel tank.
11.2.1 Gasoline
Use only high-quality brand-name gasoline with
a minimum octane rating of 90 – leaded or unlea‐
ded.
Gasoline with an ethanol content of more than
10% can cause running problems in engines with
a manually adjustable carburetor and should not
be used in such engines.
Engines equipped with M-Tronic deliver full
power when run on gasoline with an ethanol con‐
tent of up to 25% (E25).
11.2.2 Engine Oil
If you mix the fuel yourself, use only STIHL two-
stroke engine oil or another high-performance
engine oil in accordance with JASO FB, JASO
FC, JASO FD, ISO-L-EGB, ISO-L-EGC or ISO-L-
EGD.
STIHL specifies STIHL HP Ultra two-stroke
engine oil or an equivalent high-performance
engine oil in order to maintain emission limits
over the machine’s service life.
11.2.3 Mix Ratio
STIHL 50:1 two-stroke engine oil: 50 parts gaso‐
line to 1 part oil
11.2.4 Examples
Gasoline STIHL engine oil 50:1
Liters Liters (ml)
1 0.02 (20)
5 0.10 (100)
10 0.20 (200)
15 0.30 (300)
20 0.40 (400)
25 0.50 (500)
► Use a canister approved for storing fuel. Pour
oil into canister first, then add gasoline and
mix thoroughly.
11.3 Storing Fuel
Store fuel only in approved safety-type fuel can‐
isters in a dry, cool and safe location protected
from light and the sun.
Fuel mix ages – only mix sufficient fuel for a few
weeks work. Do not store fuel mix for longer than
30 days. Exposure to light, the sun, low or high
temperatures can quickly make the fuel mix
unusable.
STIHL MotoMix may be stored for up to 2 years
without any problems.
► Thoroughly shake the mixture in the canister
before fueling your machine.
WARNING
Pressure may build up in the canister – open it
carefully.
► Clean the fuel tank and canister from time to
time.
Dispose of remaining fuel and cleaning fluid
properly in accordance with local regulations and
environmental requirements.
12 Fueling
English 11 Fuel
22 0458-426-8321-B