Maintenance; Carburettor - Husqvarna 335XPT 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 carburetor for optimum
operating conditions.
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 carburetor is set to its basic setting when test run at the
factory. The basic setting is richer than the optimal setting and
should be kept during the machine's first working hours.
Thereafter the carburetor should be finely adjusted. Fine
adjustment should be carried out by a skilled technician.
NOTE! If the chain rotates while idling the T screw should be
adjusted counter-clockwise until it stops.
Recommended idling speed: 2 800 rpm.
!
WARNING! 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.
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.
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, accele-
ration, max. speed, etc.
30
– English

MAINTENANCE

L
H
T
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 needles to the mid-point between
fully in and fully out.
• Do not attempt to adjust the needles past their stops as
this can cause damage.
• 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
Turn the L needle clockwise to the stop. If the engine
accelerates poorly or idles unevenly turn the L needle anti-
clockwise until good acceleration and idling are achieved.
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.
!
WARNING! 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
affects the power and engine
speed of the saw. Too lean a
setting of the high speed
needle (H needles screwed in
too far) cause over-revving
with subsequent damage to
the saw. Turn the high speed
needle anti-clockwise to its
stop. If the engine runs
unevenly, turn the high speed
needle clockwi se until the
engine runs evenly.
The H jet is correctly adjusted when the saw "4-strokes" slightly.
If the saw "screams", it is set too lean. If smoke comes from the
muffler while the saw is "4-stroking", it is set too rich. Turn the H
needle clockwise to achieve a setting which sounds right.
Note! For optimal adjustment, contact a qualified service
agent with access to a tachometer.
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.
H