Adjusting The Carburetor; Machines With/Without Adjustable Carburetor - Stihl BR 500 Instruction Manual

Adjusting the Carburetor

Machines without Adjustable Carburetor
On certain machine versions it is no
longer necessary to adjust the
carburetor. Such machines have no
setting symbol on the shroud.
H
These machines have been set at the
factory to provide an optimum fuel-air
mixture in all locations and operating
conditions.
Adjusting idle speed
Engine stops while idling:
Turn the idle speed screw (LA)
N
slowly clockwise until the engine
runs smoothly.
Machines with Adjustable 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 and low speed
screws within fine limits.
BR 500, BR 550, BR 600
Standard Setting
Shut off the engine.
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".
Check the spark arresting screen
N
(not in all models, country-specific)
in the muffler and clean or replace if
necessary.
H
Carefully turn both adjusting screws
N
counterclockwise as far as stop:
The high speed screw (H) is 3/4 turn
N
open.
The low speed screw (L) is 3/4 turn
N
open.
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
slowly clockwise until the engine
runs smoothly.
Erratic idling behavior, engine stops
even though setting of LA screw has
been corrected, poor acceleration
Idle setting is too lean
Turn the low speed screw (L)
N
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
clockwise, no further than stop, 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 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.
NOTICE
After returning from high altitude, reset
the carburetor to the standard setting.
If the setting is too lean there is a risk of
engine damage due to insufficient
lubrication and overheating.
English
23