Stihl MS 661 C-M Instruction Manual

0458-759-8221-C
39
English 13 Mixing Fuel and Refueling the Chain Saw
Disengaging the chain brake unlocks the chain. To
disengage the chain brake:
► Pull the front hand guard toward the front handle.
You will hear an audible click when the front hand guard
reaches the unlocked position. In this position, the chain
brake is disengaged and the engine can be accelerated.
12.3 Maintaining the Chain Brake
WARNING
An improperly maintained chain brake may increase the time
needed to stop the saw chain after activation, or it may not
activate or stop the chain at all, @ 6.2. The chain brake is
subject to wear, depending on the amount of usage,
conditions under which the saw is used and other factors.
Excessive wear will reduce the effectiveness of the chain
brake and can render it inoperable.
► Your chain saw should be returned to your authorized
STIHL servicing dealer for periodic inspection and
servicing of the brake system according to the following
schedule:
– Heavy Usage: every 3 months
– Part-Time Usage: every 6 months
– Occasional Usage: every 12 months
13.1 Mixing Fuel
Information on Fuel
Your engine requires a mixture of high-quality gasoline and
2-cycle air cooled engine oil. This engine is certified to
operate on mid-grade unleaded gasoline with a minimum
octane rating of 89 and no more than 10 % ethanol and
2-cycle oil for air cooled engines at a mix ratio of 50:1.
If you mix the fuel yourself, STIHL recommends the following
2-cycle engine oils:
– STIHL HP Ultra 2-Cycle Engine Oil
NOTICE
Fuel with an octane rating below 89 may increase engine
temperatures. This, in turn, increases the risk of piston
seizure and damage to the engine. The chemical
composition of the fuel is also important.
NOTICE
Some fuel additives not only detrimentally affect elastomers
(carburetor diaphragms, oil seals, fuel lines, etc.), but
magnesium castings and catalytic converters as well. This
could cause running problems or damage the engine. For
this reason STIHL recommends that you use only quality
unleaded gasoline.
Information on Ethanol Content
WARNING
At correct idle speed, the saw chain should not move. To
reduce the risk of personal injury from loss of control and/or
contact with the running chain, have the chain saw inspected
by an authorized STIHL servicing dealer before further use
if the chain moves while the engine is idling.
0000-GXX-2933-A0
13 Mixing Fuel and Refueling the Chain
Saw

Stihl MS 661 C-M Specifications

General

Idle speed	- RPM
Motor type	2-stroke motor
Chain pitch	3/8 \
Blade length	800 mm
Product color	Black, Grey, Orange
Automatic oiling	Yes
Engine displacement	91.1 cm³
Power source	Gasoline
Sound power level	118 dB
Vibration emission	6.9 m/s²
Sound pressure level	105 dB

Weight and Dimensions

Weight	7400 g