Stihl MS 251 Manual

89MS 231, MS 231 C, MS 251, MS 251 C
: Push the carburetor (1) over the
studs (arrows) so that ends of
studs are flush with carburetor
body.
: Push the fuel hose (1) onto the
nipple (2) so that the tab (arrow)
faces the throttle shaft lever and
locates uniformly on the nipple.
– Push the carburetor fully home.
Models with manual fuel pump
: Push the new fuel hose (1) onto
the nipples (arrows).
2310RA354 TG
1
2310RA355 TG
1
2
2310RA356 TG
1
All models
– Install the filter base, b 12.3
– Install the air filter, b 12.1
– Check operation
– Set throttle trigger to full throttle
position, the throttle shutter must
be fully open.
– Reassemble all other parts in the
reverse sequence.
12.5.1 Leakage Test
In the case of problems with the
carburetor or fuel supply system,
also check and clean or replace the
tank vent, b 12.10
The carburetor can be tested for
leaks with the pump
0000 850 1300.
– Remove the carburetor, b 12.5
: Push the fuel hose (1)
1110 141 8600 on to the
nipple (2)
0000 855 9200.
: Push the fuel hose with nipple
onto the carburetor’s fuel
stub (arrow).
2310RA254 TG
1
2
– Push the pressure hose of pump
0000 850 1300 onto the nipple.
: Push the ring (1) to the right and
pump air into the carburetor until
the pressure gauge (2) indicates
a pressure of about 0.8
bar (80 kPa).
If this pressure remains constant,
the carburetor is airtight. However, if
it drops, there are three possible
causes:
1. Metering diaphragm or gasket
damaged, replace if necessary,
b 12.6.1
2. The inlet needle is not sealing
(foreign matter in valve seat,
sealing cone of inlet needle
is damaged or inlet control lever
is sticking, remove to clean,
b 12.6.2
3. Pump diaphragm or
gasket damaged, replace if
necessary, b 1 2 . 6 . 3
– Test the tank vent if necessary,
b 12.10.1
– After completing the test, push
the ring (1) to the left to vent the
system and then pull the fuel
hose off the carburetor.
– Install the filter base, b 12.3
– Reassemble all other parts in the
reverse sequence.
2
1
2310RA255 TG
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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