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Carburettor
Functioning, Basic setting, Final setting
WARNING! Do not start the saw without the
bar, chain and clutch cover (chain brake)
assembled. If you do, the clutch might come
loose and cause severe injuries.
Operation
• The carburettor governs the engine speed via the throttle. Air/
fuel are mixed in the carburettor. The air/fuel mixture is
adjustable. To take advantage of the saw’s maximum output
the setting must be correct.
• Adjusting the carburettor means the engine is adapted to
local operating conditions, e.g. climate, altitude, petrol and
the type of 2-stroke oil used.
• The carburettor has three
adjustment possibilities:
L = Low speed jet.
H = High speed jet.
T = Adjustment screw for
idling.
• The fuel quantity required in relation to the air flow, provided
by opening the throttle, is adjusted by the L and H-jets. If they
are screwed clockwise the air/fuel ratio becomes leaner (less
fuel) and if they are turned anti-clockwise the ratio becomes
richer (more fuel). A leaner mixture gives a higher engine
speed and a richer mixture give a lower engine speed.
• The T screw regulates the idling speed. If the screw T is
turned clockwise this gives a higher idling speed; anti-
clockwise a lower idling speed.
Basic setting and running in
The carburettor is adjusted to a basic setting when the saw is
tested at the factory.
254XP: The basic setting is: H = 1
1
/
2
turns respective
L = 1
1
/
4
turns.
257: The basic setting is: H = 1 turns respective
L = 1 turns.
262XP: The basic setting is: H = 1 turns respective
L = 1 turns.
To provide the engine’s components with a good level of
lubrication (running in) the carburettor should be set for a
richer fuel mixture for the first 3-4 hours of operating. To
obtain this adjust the overspeed 6-700 rpm under the
recommended max. overspeed.
If you do not have the possibility to check the overspeed using a
tachometer the H-jet should not be set for a leaner mixture than
that stated for the basic setting.
The recommended overspeed should not be exceeded.
NOTE! If the chain rotates while idling the T screw should be
adjusted anti-clockwise until it stops.
Fine adjustment
• When the saw has been ”run-in” the carburettor should be
finely adjusted. The fine adjustment should be carried out
by qualified person. First adjust the L-jet, then the idling
screw T and then the H-jet.
The following engine speed applies:
Max. overspeed Idling speed
254XP: 13.800 rpm 2.500 rpm
257: 13.500 rpm 2.500 rpm
262XP: 13.500 rpm 2.500 rpm
Conditions
• Before any adjustments are made the air filter should be
clean and the cylinder cowling fitted. Adjusting the carburettor
while a dirty air filter is in use will result in a leaner mixture
when the filter is finally cleaned. This can give rise to serious
engine damage.
• Carefully turn the L and H-jets clockwise to the bottom. Now
!
turn the jets one turn anti-clockwise. The carburettor is now
set to H = 1 and L = 1.
• Now start the saw according to the starting instructions and
run it warm for 10 minutes.
NOTE! If the chain rotates the T screw should be turned
anti-clockwise until the chain stops.
• Place the saw on a flat surface so that the bar points away
from you and so that the bar and chain do not come 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.
Final setting of the idling speed T
Adjust the idling speed with the screw T. If it is necessary to re-
adjust, 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 occurs when
the engine runs smoothly in every position. It should also be
good margin to the rpm when the chain starts to rotate.
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.
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 closed 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 of the
enginesound. Repeat this procedure with the high speed needle
H turned 1/4 turn more counter-clockwise. The saw has now
been tested with the following settings: H=±0, H=+1/4, H=+1/2
from basic adjustment. 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 ”whist-
les” 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. Turn 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 must not be exceeded.
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.
!
MAINTENANCE
L
+ 1/4
H