Husqvarna PS 50 - Manual (Page 19)

CARBURETTOR
Functioning, Basic setting, Final setting
WARNING! Do not start the saw without the hydraulic
ttank an hoses conected to the engine. If you do, the
clutch might come loose and cause severe injuries.
Functioning
• The carburettor governs the enginespeed via the throttle
trigger. In the carburettor, air/fuel is mixed. This air/fuel
mixture is adjustable. If you want to take advantage of the
maximum 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=ldle speed adjustment screw
• The fuel quantity required in proportion to the airflow the
throttle trigger level 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
rpm:s and a rich one lower rpm:s.
• The idling speed screw T regulates the position of the throttle
lever in the idling speed position. Turn the idling speed screw
clockwise gives a higher idling speed, turn it counter­
clockwise a lower idling speed.
Ч* The carburettor is adjusted to a basic setting when the saw is
tested at the factory. The basic setting is richer than the
optimum setting and shall be maintained during the first
working hours. Thereafter, do the final setting of the
carburettor. The basic setting can vary between: H=1 to 1 1/4
turn respectively L=1 to 1 1/4 turn.
NOTE! If the chain rotates in the idling position, turn the idling
speed screw counter-clockwise until the chain stops.
Final setting
• After the ’’break in”-period the final setting is to be done.
Leave the final setting to a qualified person. First adjust the
low speed needle L, Then the high speed needle H and
finally the idling speed screw T. The carburettor should be
set according to following rpm-limits:
Max. speed (no load)=11 000 rpm
Idling speed=2 500 rpm
Conditions
• Before all settings are done the air filter must be clean and
the cylinder cover mounted.
• Turn carefully (clockwise) the needles L and H to the bottom.
Turn, thereafter (counter-clockwise) the needles one turn.
The carburettor is now set: H=1 and L=1.
• Start the saw according to the starting instructions and warm
it up during 10 minutes.
NOTE! if the chain rotates in the idling position, turn the idling
speed screw counter-clockwise until the chain stops.
• Put the saw on a flat surface, the bar pointing in the opposite
direction of you. Avoid that bar and chain get into contact
with the surface or other objects.
Low speed needle L
Try to find the highest idling speed, turning the low speed
needle L clockwise respectively counter-clockwise. When the
highest speed has been found, turn the low speed needle L 1/4
turn counter-clockwise.
NOTE! If the chain rotates in the idling position, turn the idling
speed screw counter-clockwise until the chain stops.
rpm
U/min
tr/mn
o/min
r/min
Ш)
High speed needle H
The high speed needle H influences the power of the saw. A
too lean adjusted high speed needle H (high speed needle H
dosed too much) gives overrevs and damages the engine. Let
the saw run at full speed for about 10 seconds. Thereafter, turn
the high speed needle H 1/4 turn counter-clockwise. Let the
saw run again at full speed for about 10 seconds and note the
difference о the enginesound. Repeat this procedure with the
high speed neddle H turned 1/4 turn more counter-clockwise.
The saw has now been tested with the following settings: H=1,
H=1 1/4, H=1 1/2. At full speed the engine has produced a
different sound for each setting. The high speed needle H is
correctly set when the saw ”4-cycles" a little. If the saw
’’whistles" the setting is too lean. If there is too much exhaust
gas at the same time as the saw ’’4-cycles” much, the setting is
too rich. Trun the high speed needle H until the setting sounds
correct.
NOTE! For optimum setting of the carburettor, contact a
qualified servicing dealer who has a revolution counter at his
disposal. The maximum speed recommended, 11 000 rpm,
must not be exceeded.
Final setting of the idling speed T
Adjust the idling speed with the screw T. If it is necessary to
readjust, first turn the idle speed adjusting screw T clockwise,
until the chain starts to rotate. Then turn, counter-clockwise
until the chain stops. A correctly adjusted idle speed setting
(approx. 2 500 rpm) occurs when the engine runs smoothly in
every position. It should also be good margin to the rpm when
the chain starts to rotate.
CAUTION! contact your servicing dealer, if the idle
speed setting cannot be adjusted so that the chain
stops. Do not use the saw until it has been properly
adjusted or repaired.
Correctly adjusted carburettor
A correctly adjusted carburettor means that the saw
accelerates without hesitation and the saw 4-cycles a little at
max speed. Furthermore, the chain must not rotate at idling. A
too lean adjusted low speed needle L may cause starting
difficulties and bad acceleration.
A too lean adjusted high speed needle H gives lower
power=less capacity, bad acceleration and/or damage to the
engine.
A too rich adjustment of the two speed needles L and H gives
acceleration problems or too low working speed.
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