Carburettor Settings - Husqvarna 122C Workshop Manual

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Fuel system

Carburettor settings

!
WARNING!
When testing the engine in connection with carburettor adjustment,
the clutch and clutch cover must be mounted together with the shaft
and angle gear under all circumstances
Otherwise there is a risk of the clutch becoming loose resulting in
serious personal injury.
Function
The carburettor has the task of supplying a combustible fuel/air mixture to the cylin-
der.
The amount of this mixture is controlled by the throttle.
The mixture's composition of fuel and air is controlled by means of the adjustable "H"
and "L" needles.
The needles must be correctly adjusted in order for the engine to give maximum power
at different speeds, run steadily while idling and to react quickly when accelerating.
The setting of the carburettor can vary a little depending on the humidity, temperature
and air pressure.
L = Low speed needle
H = High speed needle
T = Idle adjustment screw
• The fuel quantity in relation to the air fl ow permitted by the throttle opening is
adjusted by the L and H jets. Turning the needles clockwise gives a leaner fuel
mixture (less fuel) and turning them anticlockwise gives a richer fuel mixture (more
fuel). A leaner mixture gives higher revs while a richer mixture gives less revs.
• The T-screw regulates the position of the throttle while the engine is idling. Turning
the screw clockwise gives a higher idling speed while turning it anticlockwise gives
a lower idling speed.
Basic setting
The carburettor is set to its basic setting when test run at the factory. The basic setting
is "richer" than the optimal setting (fast idle speed is 600–800 rpm under the recommen-
ded max. speed) and should be kept during the engine's fi rst working hours. Thereafter
the carburettor should be fi ne tuned.
The basic setting is: H = 1 turn open, L = 1,5 turns open.
530 03 55-60
Both of the high and low speed jets in the carburettor can only be adjusted using the
special tool 530 03 55-60.
To carry out adjustment when replacing needles or the entire carburettor the engine
must be under load. This is achieved by fi tting a standard trimmer with the specifi ed
length (defi ned by the blade on the trimmer guard) and diameter of the trimmer cord.
Consequently, the stated speed will be much lower than with "normal" carburettor ad-
justment when the engine may run freely.
After replacing the needles or the entire carburettor on a CARB-EPA approved engine,
adjustment must be carried out according to the instructions below.
The combiguard or trim guard must be fi tted when adjusting the H-needle.
502 71 14-01