Stihl MS 251 Manual

18 MS 231, MS 231 C, MS 251, MS 251 C
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
Condition Cause Remedy
Engine does not start easily, stalls
at idle speed, but operates normally
at full throttle
Oil seals in engine damaged Replace the oil seals
Engine pan leaking or
damaged (cracks)
Inspect engine pan, re-seal or
replace if necessary.
Intake manifold damaged / bore
blocked
Clean bore or install new manifold.
Engine does not deliver full power
or runs erratically
Piston rings worn or broken Fit 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
Intake manifold damaged / bore
blocked
Clean bore or install new manifold.
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
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Stihl MS 251 Specifications

General

Idle speed	2800 RPM
Motor type	2-stroke motor
Chain pitch	1/308 \
Blade length	450 mm
Product color	Black, Grey, Orange
Motor speed (max)	10000 RPM
Oil tank capacity	0.2 L
Fuel tank capacity	0.39 L
Engine displacement	45.6 cm³
Kickback protection	Yes
Engine power	3 hp
Power source	Gasoline
Sound power level	114 dB
Vibration emission	3.9 m/s²
Sound pressure level	103 dB

Weight and Dimensions

Weight	4900 g