Stihl MS 251 Manual

33MS 231, MS 231 C, MS 251, MS 251 C
6.2 Leakage Test
Defective oil seals and gaskets or
cracks in castings are the usual
causes of leaks. Such faults allow
supplementary air to enter the
engine and upset the fuel-air
mixture.
This makes adjustment of the
prescribed idle speed difficult, if not
impossible.
Moreover, the transition from idle
speed to part or full throttle is not
smooth.
Always perform the vacuum test
first and then the pressure test.
The engine can be checked
thoroughly for leaks with the pump
0000 850 1300.
6.2.1 Preparations
– Remove the shroud, b 6.4
– Pull off the boot and unscrew the
spark plug.
– Set the piston to top dead center.
This can be checked through the
spark plug hole.
2310RA079 TG
1
: Fit the spark plug (1) and tighten
it down firmly.
– Remove the muffler and gasket,
b 6.1
: Fit the test flange (1)
5910 855 4201 on cylinder
exhaust port.
: Fit the screws (2)
– do not tighten down yet.
Flange (1) 4224 893 2501 can be
modified as shown.
a = 13 mm
b = 39.25 mm
c=6mm
2
2310RA072 TG
1
2
c
b
2710RA164 TG
a
: Fit the sealing plate (1)
0000 855 8106 between the
cylinder exhaust port and
flange (2).
: Tighten the screws (3)
moderately.
The sealing plate must completely
fill the space between the two
screws.
– Remove the carburetor, b 12.5
: Make sure the washer (1) is in
place.
2
3
2310RA074 TG
1
3
2310RA073 TG
1
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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