Stihl MS 251 Manual

90 MS 231, MS 231 C, MS 251, MS 251 C
12.6 Servicing the Carburetor
12.6.1 Metering Diaphragm
– Troubleshooting, b 3.6
– Remove the carburetor, b 12.5
: Take out the screws (arrows).
: Remove the end cover (1).
If the gasket and diaphragm are
stuck to the carburetor, remove
them very carefully.
: Check the O-ring (1) and replace
it if necessary
: On versions with a manual fuel
pump, check the nipple (2) and
replace the end cover if
necessary.
2310RA256 TG
1
2310RA257 TG
1
2
: Carefully separate the metering
diaphragm (1) and gasket (2).
The diaphragm material is
subjected to continuous alternating
stresses and eventually shows
signs of fatigue. i.e. the diaphragm
distorts and swells and has to be
replaced.
– Check the metering diaphragm
for signs of damage and wear.
Install a new gasket.
Installing
– Note installed positions of
metering diaphragm (2) and
gasket (1).
: Position the gasket (1) and
metering diaphragm (2) so that
pegs (arrows) engage the small
holes in the tabs.
2310RA256 TG
12
2310RA259 TG
1
2
: Position the end cover (1) so that
the stub (3) points in the direction
of the choke shutter and the
holes line up.
: Fit the screws (2) but do not
tighten them down yet.
– Check position of metering
diaphragm and gasket, then
tighten down the screws firmly in
a crosswise pattern.
Take care not to damage the O-
ring (arrow).
– Reassemble all other parts in the
reverse sequence.
12.6.2 Inlet Needle
– Remove the metering
diaphragm,
b 12.6.1
2310RA260 TG
2
2
2
2
1
3
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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