Adjusting The Carburetor - Stihl BR 450 Instruction Manual

12 Adjusting the Carburetor

3
► Remove the filter element (3).
► Replace dirty or damaged filters.
► Fit the new filter in the filter housing.
► Fit the filter cover.
► Fit the screws and tighten them down firmly.
12 Adjusting the Carburetor
12.1 General Information
The carburetor comes from the factory with a
standard setting.
This setting provides an optimum fuel-air mixture
under most operating conditions.
12.2 Preparations
► Shut off the engine.
► Check the air filter and clean or replace if nec‐
essary.
► Check that the throttle cable is properly adjus‐
ted – readjust if necessary – see chapter on
"Adjusting the Throttle Cable".
► Check the spark arresting screen (not in all
models, country-specific) in the muffler and
clean or replace if necessary.
12.3 Standard Setting
H
► Turn high speed screw (H) counterclockwise
as far as stop (no more than 3/4 turn).
► Turn the low speed screw (L) clockwise as far
as stop, then turn it back 3/4 turn.
12.4 Adjusting Idle Speed
► Carry out the standard setting.
0458-391-8321-B
L
► Start and warm up the engine.
12.4.1 Engine stops while idling
► Turn the idle speed screw (LA) slowly clock‐
wise until the engine runs smoothly.
12.4.2 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) counterclock‐
wise, no further than stop, until the engine
runs and accelerates smoothly.
12.4.3 Erratic idling behavior
Idle setting is too rich
► Turn the low speed screw (L) 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).
12.5 Fine Tuning for Operation at
High Altitude
A slight correction of the setting may be neces‐
sary if the engine does not run satisfactorily:
► Carry out the standard setting.
► Warm up the engine.
► Turn high speed screw (H) slightly clockwise
(leaner) – no further than stop.
English
L
LA
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