Engine Management; Adjusting The Carburetor - Stihl FS 500 Instruction Manual

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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.
26

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.
Changing the setting of the high speed
screw alters the engine's power output
and the maximum off-load engine
speed.
If the setting is too lean there is a
risk of engine damage due to
insufficient lubrication and
overheating.
Standard Setting
N
Stopping the engine
N Mount the cutting attachment.
N Check the air filter and clean or
replace as necessary.
N Check that the throttle cable is
properly adjusted – readjust if
necessary – see chapter on
"Adjusting the Throttle Cable".
N Check the spark arresting screen
(not in all versions) and clean or
replace as necessary.
H
1/4 1/4
H L
LA
N
Turn high speed screw (H)
counterclockwise as far as stop (no
more than 1/4 turn).
N Turn the low speed screw (L)
carefully counterclockwise as far as
stop, no more than a 1/4 turn.
N Warm up the engine.
N Adjust idle speed with the idle speed
screw (LA) so that the cutting
attachment does not rotate.
Aadjusting Idle Speed
Engine stops while idling
N Carry out standard setting on low
speed screw (L).
N Turn the idle speed screw (LA)
slowly clockwise until the engine
runs smoothly – the cutting
attachment must not rotate.
FS 500, FS 550
L