Operators Manual

English – 29
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 turn respective L = 1 turn.
262XP: The basic setting is: H = 1 turn respective L = 1 turn.
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 600-700 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
Changing the type of fuel
Fine tuning may be required if the chain saw, after changing the type of
fuel, performs differently with regard to starting, acceleration, max.
speed, etc.
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 engine-
sound. 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 ”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. 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 accelera-
tion. 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 accele-
ration problems or too low working speed.
!
MAINTENANCE
L
+ 1/4
H