Engine Management; Adjusting The Carburetor - Stihl FS 120 Instruction Manual

Engine Management

Exhaust emissions are controlled by the
design of the fundamental engine
parameters and components (e.g.
carburation, ignition, timing and valve or
port timing) without the addition of any
major hardware.
FS 120, FS 120 R, FS 200, FS 250, FS 250 R

Adjusting the Carburetor

The carburetor comes from the factory
with a standard setting.
This setting provides an optimum fuel-air
mixture under most operating
conditions.
With this carburetor it is only possible to
adjust the high speed screw (H) within
fine limits.
Standard Setting
Shut off the engine
N
Mount the cutting attachment.
N
Check the air filter and replace it if
N
necessary.
Check that the throttle cable is
N
properly adjusted – readjust if
necessary – see chapter on
"Adjusting the Throttle Cable".
Have spark arresting screen
N
checked.
L
H
1
LA
Turn high speed screw (H)
N
counterclockwise as far as stop (no
more than 3/4 turn).
Turn the low speed screw (L)
N
carefully clockwise as far as stop,
then turn it back 1 turn.
Start and warm up the engine if
N
necessary.
Adjust idle speed with the idle speed
N
screw (LA) so that the cutting
attachment does not rotate.
Fine Tuning
A slight correction of the setting of the
high speed screw (H) may be necessary
if engine power is not satisfactory when
operating at high altitude, sea level or
after changing the cutting attachment.
English
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