FS 400, FS 450
English
28
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
N Shut off the engine.
N Mount the cutting attachment.
N Check the air filter and clean or 
replace if necessary.
N Check that the throttle cable is 
properly adjusted – readjust if 
necessary – see chapter on 
"Adjusting the Throttle Cable".
Standard Setting
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 until it is against 
its seat, then turn it back 1 full turn
Adjusting Idle Speed
N Carry out the standard setting.
N Start and warm up the engine.
Engine stops while idling
N Turn the idle speed screw (LA) 
clockwise until the engine runs 
smoothly – the cutting attachment 
must not rotate.
Cutting attachment rotates when engine 
is idling
N Turn the idle speed screw (LA) 
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
N Turn the low speed screw (L) 
carefully counterclockwise, no 
further than stop, until the engine 
runs and accelerates smoothly.
Erratic idling behavior
Idle setting is too rich
N Turn the low speed screw (L) 
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:
N Carry out the standard setting.
N Warm up the engine.
N Turn high speed screw (H) slightly 
clockwise (leaner) – no further than 
stop.
Adjusting the Carburetor