Instruction Manual
Table Of Contents
- STIHL MS 231, 251
- 1 Guide to Using this Manual
- 2 Safety Precautions
- 3 Reactive Forces
- 4 Working Techniques
- 5 Cutting Attachment
- 6 Mounting the Bar and Chain (side chain tensioner)
- 7 Mounting the Bar and Chain (quick chain tensioner)
- 8 Tensioning the Saw Chain (side chain tensioner)
- 9 Tensioning the Saw Chain (quick chain tensioner)
- 10 Checking Chain Tension
- 11 Fuel
- 12 Fueling
- 13 Chain Lubricant
- 14 Filling Chain Oil Tank
- 15 Checking Chain Lubrication
- 16 Chain Brake
- 17 Winter Operation
- 18 Starting / Stopping the Engine
- 18.1 Positions of Master Control Lever
- 18.2 Setting the Master Control Lever
- 18.3 Fuel pump
- 18.4 Holding the Saw
- 18.5 Cranking
- 18.6 Starting the Saw
- 18.7 When engine begins to fire
- 18.8 As soon as the engine runs
- 18.9 At very low outside temperatures
- 18.10 Stopping the engine
- 18.11 If the engine does not start
- 19 Operating Instructions
- 20 Taking Care of the Guide Bar
- 21 Shroud
- 22 Air Filter System
- 23 Cleaning the Air Filter
- 24 Adjusting the Carburetor
- 25 Spark Plug
- 26 Storing the Machine
- 27 Checking and Replacing the Chain Sprocket
- 28 Maintaining and Sharpening the Saw Chain
- 29 Maintenance and Care
- 30 Minimize Wear and Avoid Damage
- 31 Main Parts
- 32 Specifications
- 33 Ordering Spare Parts
- 34 Maintenance and Repairs
- 35 Disposal
- 36 EC Declaration of Conformity
► Check chain tension frequently – see chapter
on "Operating Instructions".
10 Checking Chain Tension
142BA064 KN
► Shut off the engine.
► Wear work gloves to protect your hands.
► The chain must fit snugly against the under‐
side of the bar and it must still be possible to
pull the chain along the bar by hand when the
chain brake is released.
► If necessary, retension the chain.
A new chain has to be retensioned more often
than one that has been in use for some time.
► Check chain tension frequently – see chapter
on "Operating Instructions".
11 Fuel
The engine requires a mixture of gasoline and
engine oil.
WARNING
Avoid direct skin contact with fuel and breathing
in of gasoline fumes.
11.1 STIHL MotoMix
STIHL recommends using STIHL MotoMix. This
pre-blended fuel is free of benzene and lead, is
distinguished by a high octane rating, and
always provides the proper mixing ratio.
STIHL MotoMix uses STIHL HP Ultra two-stroke
engine oil for optimum engine life.
MotoMix is not available in all markets.
11.2 Mixing fuel
NOTICE
Unsuitable fuels or a mixing ratio that deviates
from the specification can lead to severe engine
damage. The engine, seals, fuel lines and fuel
tank may be damaged if low-quality gasoline or
engine oil is used.
11.2.1 Gasoline
Use only high-quality gasoline with an octane rat‐
ing of at least 90 ROC – leaded or unleaded.
Gasoline with an alcohol component exceeding
10% can cause impaired engine performance in
engines with manually adjustable carburetors
and thus should not be used in these engines.
Engines with M-Tronic deliver full engine per‐
formance using gasoline with an alcohol compo‐
nent of up to 27% (E27).
11.2.2 Engine oil
If you mix the fuel yourself, use only STIHL two-
stroke engine oil or another high-performance
engine oil classified as 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 Mixing ratio
with STIHL two-stroke engine oil 1:50; 1:50 =
1 part oil + 50 parts gasoline
11.2.4 Examples
Quantity of gaso‐
line
STIHL two-stroke
engine oil 1:50
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)
► Pour oil into an approved safety fuel canister
first, then add gasoline and mix thoroughly
11.3 Storing fuel mixture
Store in approved safety fuel canisters only in a
dry, cool and secure place protected against light
and sunlight.
10 Checking Chain Tension English
0458-737-0121-C 19