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Stihl FS 55 Instruction Manual: Adjusting The Carburetor

Stihl trimmer instruction manual.
Also See for FS 55:
Instruction manual - 106 pages

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 within fine
limits.
Standard Setting
N
Stopping the Engine
N
Mounting the cutting attachment
N
Check the air filter and replace it if
necessary.
N
Have the spark arrestor checked –
see "Inspection and Maintenance
by Dealer"
32
H
L
LA
N
Turn high speed screw (H)
counterclockwise as far as stop (no
more than 3/4 turn).
N
Turn the low speed screw (L)
carefully clockwise as far as stop,
then turn it back 1.5 turns.
N
Start and warm up the engine if
necessary.
N
Adjust idle speed with the idle speed
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.
Rule of thumb:
Turn the high speed screw (H) about
one quarter of a turn for every 1000 m
(3300 ft) change in altitude.
Conditions for adjustment
Adjust the high speed screw (H)
only if you are using a mowing
head, making sure the cutting
lines are full length (as far as the
line limiter blade on the deflector).
If a metal cutting attachment is
mounted, use the standard setting
and adjust the high speed
screw (H) as described above
under "Rule of thumb".
N
Carry out the standard setting.
N
Start the engine and, with the
mowing head mounted, warm it up
for about 3 minutes.
N
Open the throttle wide.
At high altitude
N
Turn the high speed screw (H)
clockwise (leaner), no further than
stop, until there is no further
noticeable increase in engine
speed.
At sea level
N
Turn the high speed screw (H)
counterclockwise (richer), no further
than stop, until there is no further
noticeable increase in engine
speed.
It is possible that maximum engine
speed may be reached with the standard
setting in each case.
FS 55, FS 55 C, FS 55 R, FS 55 RC

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