36 – English
Carburettor
12.1.5 Adjustment
Adjusting the carburettor means adapting the
engine to local conditions, e.g. the climate, altitude,
petrol and the type of 2-stroke oil. The carburettor is
fitted with three adjustment possibilities:
L = Low speed jet
H = High speed jet
T = Adjuster screw for idling
The quantity of fuel in relation to the air flow permit-
ted by the throttle opening is adjusted with the L
and H jets. Turning them clockwise gives a leaner
fuel mixture (less fuel) and turning them anticlock-
wise gives a richer air/fuel mixture (more fuel).
A lean mixture gives a higher speed, while a rich
mixture gives a lower speed.
The T-screw regulates the position of the throttle
while
the engine is idling. Turning the T-screw clockwise
gives a higher idling speed, while turning it anti-
clockwise gives a lower idling speed.
Basic settings and running-in
The basic carburettor settings are used for test run-
ning in the factory. The basic settings are H = 1 1⁄4
and L = 1 1⁄4 turns respectively.
To ensure that the engine components receive
adequate lubrication (running-in) the carburettor
should be set to a somewhat richer fuel mixture for
the first 3-4 hours the chainsaw is used. To achieve
this, the max. overspeed is adjusted to 6-700 rpm
less than the recommended max. overspeed.
If it is not possible to check the max. overspeed
with a tachometer then the H-jet should not be set
to a leaner mixture than stated in the basic settings.
The recommended max. overspeed must not be
exceeded.
WARNING!
The bar, chain and clutch cover
must be fitted before the chainsaw
is started, otherwise the clutch can
work loose and cause personal
injury.
WARNING!
Wear ear-muffs when making
adjustments with the engine
running.
NOTE! If the chain goes round at idling
speed the T-screw should be turned anti-
clockwise until it stops.
L
H
T
Fine adjustment of the carburettor should be carried
out after the engine has been “run-in”. First adjust
the L-jet, then the idling speed’s T-screw, and finally
the H-jet. The following speed recommendations
apply:
Max. overspeed
Idling
speed
390XP 13000 rpm
2700 rpm
Conditions
The air filter should be clean and the cylinder
cover fitted when adjustments are made. Adjusting
the carburettor with a dirty air filter will give a fuel
mixture that is too lean the next time the air filter is
cleaned. This can result in serious damage to the
engine.
Carefully screw in (clockwise) the L and H jets until
they bottom. Now screw out (anticlockwise) the jets
1 turn. The carburettor now has the setting H = 1
and L = 1. Start the chainsaw according to the start-
ing instructions and run warm for 10 minutes.
Place the chainsaw on a flat surface so that the
bar points away from you and so that the chain and
bar are not in contact with the surface or any other
object.
NOTE! If the chain goes round at idling
speed the T-screw should be turned anti-
clockwise until it stops.
