Stihl MS 251 Manual

96 MS 231, MS 231 C, MS 251, MS 251 C
This completes the basic setting of
the high speed screw H and the low
speed screw L .
The setting of the high speed
screw H is fixed when the limiter
cap (1) is flush with the carburetor
body.
12.7.2 Standard setting
The limiter cap must not be
removed for the standard setting.
Always perform the following steps
before carrying out any
adjustments:
– Troubleshooting, b 3.6
– Check chain tension and adjust if
necessary.
– Inspect the spark arresting
screen (if fitted) and clean or
replace if necessary, b 3.7 or
b 6.1
2310RA285 TG
1
– Check the air filter and clean or
replace if necessary, b 12.1
Standard setting
– Shut off the engine.
– Turn the high speed screw (H)
slowly counterclockwise as far as
stop, but not more than
a 3/4 turn.
– Turn the low speed screw (L)
slowly clockwise as far as stop,
then turn it back
1 full turn.
Check running behavior:
The engine must idle and
accelerate smoothly.
Adjusting engine idle speed
– Carry out standard setting.
– Warm up the engine.
Engine stops while idling
– Turn the idle speed screw (LA)
clockwise until the chain starts
running, then turn it back 1 full
turn.
Saw chain runs while engine is
idling
– Turn the idle speed screw (LA)
counterclockwise until the chain
stops running, then turn it back
1full turn.
Erratic idling behavior, poor
acceleration
(although standard setting is
correct)
Idle setting too lean.
– Warm up the engine.
– Turn low speed screw (L)
counterclockwise until the engine
runs and accelerates smoothly.
It is usually necessary to change the
setting of the idle speed screw (LA)
after every correction to the low
speed screw (L).
Adjustment for operation at high
altitude
A minor correction may be
necessary if engine power is not
satisfactory when operating at high
altitude.
– Check standard setting.
– Warm up the engine.
– Turn the high speed screw (H)
clockwise (leaner) – no further
than stop.
Turn the adjusting screws only very
slightly. Even minor adjustments
can noticeably affect engine running
behavior.
If the setting is made too lean there
is a risk of engine damage as a
result of lack of lubrication and
overheating.
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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