Stihl FS 120 Manual

5/20/2018
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If this pressure remains constant,
the carburetor is airtight. However,
if it drops, there are two possible
causes:
1. The inlet needle is not sealing
(foreign matter in valve seat or
sealing cone of inlet needle is
damaged or inlet control lever
sticking).
2. The metering diaphragm is
damaged.
In either case the carburetor must
be removed and serviced - see
"Carburetor" handbook.
- After completing test, open the
vent screw and pull the fuel hose
off the elbow connector.
- Install the carburetor -see 8.2.1.
FS 400/450, FR 450
- Push the fuel hose onto the
elbow connector.
- Fit the shroud -see 4.1.
Standard setting
If the carburetor has to be
adjusted from scratch, first carry
out the standard setting.
- Carefully screw in both adjusting
screws clockwise until they are
hard against their seats.
Now make the following adjust-
ments:
H= Open high speed screw (1)
one full turn
L
= Open low speed screw (2)
one full turn
A slight correction to this setting
may be necessary at high altitudes
(mountains) or near sea level. Use
the following procedure:
- Mount approved cutting tool.
- Check the air filter, replace if
necessary.
- Check spark arresting screen,
clean or replace as necessary.
- Start the engine and allow it to
warm up.
Turn high speed screw(H)
clockwise for leaner mixture at
high altutude,
or counterclockwise for richer
mixture at sea level.
Turn screw slowly and carefully –
slight changes have a noticeable
effect on engine running behavior.
Adjusting idle speed
Engine stops while idling:
- Carry out standard setting.
Turn the idle speed screw(LA)
clockwise until cutting tool begins
to rotate, and then turn screw back
one half turn.
Turn the idle speed screw(LD)
clockwise until engine runs
smoothly – cutting tool must not
rotate.
Cutting tool rotates while
engine is idling:
- Carry out standard setting.
Turn the idle speed screw(LA)
counterclockwise until cutting tool
stops rotating – and then turn it
about another one full turn in the
same direction.
H
 L
LA
2
5
0
R
A
2
2
0
1 2
3
V
A
2
5
0
R
A
2
2
1
1
H
 L
LD
V
A
8.2.4 Adjusting
(three screws)
42 FS 120, 200, 300, 350, 400, 450, FR 350, 450

Stihl FS 120 Specifications

General

Power source	Gasoline
Type	Brush cutter
Cordless	Yes
Head type	Nylon line
Handle type	U-type handle
Engine power	1.8 hp
Product color	Black, Metallic, Orange
Uncertainty K	2 m/s²
Sound power level	110 dB
Fuel tank capacity	0.64 L
Vibration emission	4.9 m/s²
Engine displacement	30.8 cm³
Sound pressure level	98 dB
Cutting diameter (max)	- mm

Weight and Dimensions

Length	1760 mm
Weight	6300 g