Stihl MS 661 C-M User Manual

17MS 661, MS 661 C-M
3.7 Engine
Always check and, if necessary,
repair the following parts before
looking for faults on the engine:
- Air filter, fuel system
- Carburetor, ignition system
- Check M-Tronic with STIHL
MDG 1 and troubleshooting chart
Condition Cause Remedy
Engine does not start easily, stalls
at idle speed, but operates normally
at full throttle
Oil seals in crankcase damaged Install new oil seals
Crankcase leaking or damaged
(cracks)
Seal or replace the crankcase
Engine does not deliver full power
or runs erratically
Piston rings worn or broken Install new piston rings
Muffler / spark arresting screen
carbonized
Clean the muffler (inlet and
exhaust), replace spark arresting
screen, replace muffler if necessary
Air filter dirty Clean or replace air filter
Fuel hose kinked or torn Fit new hose or position it free from
kinks
Decompression valve is not closed Close and check decompression
valve, replace if necessary
Engine overheating Insufficient cylinder cooling. Air
inlets in fan housing blocked or
cooling fins on cylinder very dirty
Thoroughly clean all cooling air
openings and the cylinder fins
Air inlet in fan housing dirty Clean air inlet on fan housing

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