Adjusting The Carburetor - Stihl FS 450 Instruction Manual

English

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".
28
Standard Setting
L
H
1
3/4
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 until it is against
its seat, then turn it back 1 full turn
Adjusting Idle Speed
Carry out the standard setting.
N
Start and warm up the engine.
N
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
(despite correction to setting of LA
screw).
Idle setting is too lean
Turn the low speed screw (L)
N
carefully counterclockwise, no
further than stop, until the engine
runs and accelerates smoothly.
Erratic idling behavior
Idle setting is too rich
Turn the low speed screw (L)
N
carefully clockwise, no further than
stop, until the engine runs smoothly
and still accelerates satisfactorily.
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 engine does not run
satisfactorily:
Carry out the standard setting.
N
Warm up the engine.
N
Turn high speed screw (H) slightly
N
clockwise (leaner) – no further than
stop.
FS 400, FS 450