Adjusting The Carburetor - Stihl FS 250 Instruction Manual

Adjusting the Carburetor

General Information
The carburetor comes from the factory
with a standard setting.
This setting provides an optimum fuel-air
mixture under most operating
conditions.
Preparations
Shut off the engine.
N
Mount the cutting attachment.
N
Check the air filter and clean or
N
replace if necessary.
Check that the throttle cable is
N
properly adjusted – readjust if
necessary – see chapter on
"Adjusting the Throttle Cable".
Standard Setting
High speed screw (H) = 1 1/2
–
Low speed screw (L) = 1
–
FS 250, FS 250 R
L
H
Turn the high speed screw (H)
N
carefully clockwise until it is against
its seat, then turn it back 2 full turns.
Turn the low speed screw (L)
N
carefully clockwise as far as stop,
then turn it back 1 turn
Adjusting Idle Speed
Carry out standard setting.
N
Start and warm up the engine.
N
LA
Engine stops while idling
Turn the idle speed screw (LA)
N
clockwise until the engine runs
smoothly – the cutting attachment
must not rotate.
Cutting attachment rotates when engine
is idling
Turn the idle speed screw (LA)
N
counterclockwise until the cutting
attachment stops moving and then
turn the screw another 1/2 to 1 full
turn in the same direction.
WARNING
If the cutting attachment continues to
rotate when the engine is idling, have
your machine checked and repaired by
your servicing dealer.
Erratic idling behavior, poor acceleration
(even though setting of LA screw is
correct).
Idle setting is too lean
Turn the low speed screw (L)
N
counterclockwise, no more than 1/2
turn, until the engine runs and
accelerates smoothly.
Erratic idling behavior
Idle setting is too rich
Turn the low speed screw (L)
N
clockwise, no more than 1/2 turn,
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).
Fine Tuning for Operation at High
Altitude
A slight correction of the setting may be
necessary if the engine does not run
satisfactorily:
English
31