Husqvarna 51, Operator'S Manual

English – 

29

Carburetor

MAINTENANCE

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.

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.

Functioning, Basic setting, Final setting

Operation

• The carburetor governs the engine speed via the throttle. Air/

fuel are mixed in the carburetor. The air/fuel mixture is
adjustable. To take advantage of the engine’s optimal output
the setting must be correct.

• The setting of the carburetor means that the engine is

adapted to local conditions, for example, the climate, altitude,
fuel and the type of 2-stroke oil.

• The carburetor 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 counter-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; counter-
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: 2 500 rpm.

Low speed needle L

Turn the low speed needle L clockwise until the stop. If the
engine has bad acceleration or erratic idling, turn the L needle
counter-clockwise until good idling and acceleration.
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.

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. Turn the high
speed needle H counter-
clockwise until the stop. If the
engine runs roughly, turn the
high speed needle slowly the
minimum amount clockwise
until the engine runs smoothly.
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 carburetor, contact a qualified servicing dealer who
has a revolution counter at his disposal.

Correctly adjusted carburetor

A correctly adjusted carburetor 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

Conditions

• Before any adjustments are made the air filter should be

clean and the cylinder cowling fitted. Adjusting the carburetor
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 needle to the mid point.
• Do not attempt to adjust the needles beyond the stops as

damage can occur.

• 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
counter-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.

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 carburetor 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.

!

!

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.

!