Maintenance; Carburettor - Husqvarna 250PS Operator's Manual

Carburettor

Your Husqvarna product has been designed and
manufactured to specifications that reduce harmful
emissions.
After your unit has been run 8-10 tanks of fuel the engine
has broken in. To ensure that your unit is at peak
performance and producing the least amount of harmful
emissions after break in, have your authorized servicing
dealer, who has a revolution counter at his disposal, to adjust
your carburettor for optimum operating conditions.
!
WARNING!
Do not start the engine without the
hydraulic tank and hoses connected. If
you do, the clutch might come loose and
cause severe injuries.
Functioning
• The carburettor governs
the engine speed via the
throttle trigger. In the
carburettor, air/fuel is
mixed. This air/fuel
mixture is adjustable. If
you want to take advan-
tage of the maximum
power output of the
engine, the setting must be
correct.
• The setting of the
carburettor means that the
engine is adjusted to local
conditions, for example
climate, altitude, petrol
and type of two-stroke oil.
• The carburettor has three adjustment possibilities:
L = Low speed needle
H = High speed needle
T = Idle speed adjustment screw
• The fuel quantity required in proportion to the airflow the
throttle trigger position allows is adjusted by means of the
L- and H-needles. Turning the needles clockwise gives a
leaner fuel mixture (less fuel), turning them counter-
clockwise gives a richer fuel mixture (more fuel). A lean
mixture gives higher rpms and a rich one lower rpms.
• The idling speed screw (T) regulates the position of the
throttle lever in the idling speed position. Turning the
idling speed screw clockwise gives a higher idling speed,
turning it counter-clockwise gives a lower idling speed.
Basic setting
The carburettor is adjusted to a basic setting at the factory.
The basic setting is richer than the optimum setting and shall
be maintained during the first working hours. The carburettor
should be fine adjusted. The basic setting can be varied
between H = 1 to 1 1/4 turns and L = 1 1/4 turns.
NOTE!
If the chain rotated during idling the T-screw should be
turned anti-clockwise until the chain stops.
20
– English

MAINTENANCE

L
H
T
Fine adjustment
• When the tree pruner is "run in" the carburettor should be
fine adjusted. Fine adjustment should be carried out by
trained personnel. The L-nozzle is adjusted first, then the
H-nozzle and finally the idling screw T. The following revs
recommendations are applicable:
Max. race revs
Idling revs
Prerequisites
• During all adjustment the air filter should be clean and the
cylinder casing fitted.
• Carefully screw in (clockwise) the L- and H-nozzles to the
bottom.
Then unscrew (anti-clockwise) the nozzles 1 turn. The
carburettor now has the setting H = 1 and L = 1.
• Start the pruner as per the starting instructions and run for
about 10 minutes until it is warm.
NOTE!
If the chain rotates during idling the T-screw should be turned
anti-clockwise until the chain stops.
• Place the pruner on a flat surface so that the blade is
pointing away from you and not in contact with the surface
or any other object.
Low speed nozzle L
Search for the highest idling revs by means of slowly screwing
the low speed nozzle clockwise or anti-clockwise. When the
highest revs have been found screw the L-nozzle anti-
clockwise 1/4 turn.
NOTE!
If the chain rotates during idling the T-screw should be turned
anti-clockwise until the chain stops.
High speed nozzle H
The high speed nozzle H affects the engine output and revs. A
lean mixture of the high speed nozzle (H-nozzle screwed in
too far) gives over-revs resulting in damage to the engine.
Run the engine at full throttle for about 10 seconds.
The H-nozzle is correctly adjusted when the saw putters
slightly. If there is excessive smoke from the exhaust while the
pruner is puttering excessively the setting is too rich. Turn the
H-nozzle clockwise until the setting sounds right.
NOTE!
To obtain an optimal setting contact a professional with access
to a tachometer.
Fine adjustment of idling T
The setting of the idling speed is done with the screw marked
T. If adjustment is necessary screw in (clockwise) the idling
screw T with the engine running until the chain starts to
rotate. Then open (anti-clockwise) until the chain stands still.
The correct setting of the idling revs is obtained when the
engine works regularly in all positions with a good margin
until the revs when the chain begins to rotate.
!
WARNING!
Contact your servicing dealer, if the idle
speed setting cannot be adjusted. Do not
use the pruner until it has been properly
adjusted or repaired.
= 11 000, rpm
= 2 500, rpm