Fueling - Stihl MS 261 C-M Instruction Manual

English
Your engine requires a mixture of high-quality
premium gasoline and high-quality two-stroke
air-cooled engine oil.
Use premium branded unleaded gasoline with a
minimum octane rating of 89 (R+M)/2.
Note: Models equipped with a catalytic converter
require unleaded gasoline. A few tankfuls of lea‐
ded gasoline can reduce the efficiency of the cat‐
alytic converter by more than 50%.
Fuel with a lower octane rating may result in pre‐
ignition (causing "pinging") which is accompa‐
nied 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 detrimen‐
tally 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 equiva‐
lent high-quality two-stroke air-cooled engine oils
for mixing.
We recommend STIHL 50:1 two-stroke engine
oil since it is specially formulated for use in
STIHL engines.
To ensure the maximum performance of your
STIHL engine, use a high quality 2-cycle engine
oil. To help your engine run cleaner and reduce
harmful carbon deposits, STIHL recommends
using STIHL HP Ultra 2-cycle engine oil or ask
your dealer for an equivalent fully synthetic 2-
cycle engine oil.
To meet the requirements of EPA and CARB we
recommend to use STIHL HP Ultra oil.
Do not use BIA or TCW (two-stroke water
cooled) mix oils!
18
Use only STIHL 50:1 heavy-duty engine oil or an
equivalent quality two-stroke engine oil for the
fuel mix in models equipped with a catalytic con‐
verter.
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 mix‐
ture.
The fuel tank and the canister in which fuel mix is
stored should be cleaned from time to time.
9.1 Fuel mix ratio
Only mix sufficient fuel for a few days work, not
to exceed 30 days of storage. Store in approved
safety fuel-canisters only. When mixing, pour oil
into the canister first, and then add gasoline.
Examples
Gasoline Oil (STIHL 50:1 or equiva‐
lent high-quality oils)
liters liters
1 0.02
5 0.10
10 0.20
15 0.30
20 0.40
25 0.50
Dispose of empty mixing-oil canisters only at
authorized disposal locations.

10 Fueling

10.1 Preparing the machine
► Before fueling, clean the cap and the area
around it to ensure that no dirt falls into the
fuel tank
► Always position the machine so that the cap is
facing upwards
10 Fueling
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0458-153-8221-C