Husqvarna FR335, Руководство по ремонту

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32
3
Fuel system
333/335
336
The needles must be correctly adjusted in order for the engine to give maximum
power at diff erent speeds, run steadily while idling and to react quickly when accele-
rating.
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 ad-
justed 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. Tur-
ning the screw clockwise gives a higher idling speed while turning it anticlockwise
gives a lower idling speed.
Carburettor settings
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.
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.
!
Basic setting
The carburettor is set to its basic setting when test run at the factory. The basic set-
ting is “richer” than the optimal setting (fast idle speed is 600–800 rpm under the re-
commended max. speed) and should be kept during the engine’s fi rst working hours.
Thereafter the carburettor should be fi ne tuned.
The default setting is:
Model H L
135 2.0 0.75
333 2.0 (EL-36D) 1.0 (EL-36D)
335 2.0 (EL-36D) 1.0 (EL-36D)
336 2.0 0.75
535 2.0 (EL-36D) 1.0 (EL-36D)
The H and L needles on the carburettor can be adjusted within extremely tight limits,
to among others, comply with the stringent demands with regard to the hydrocarbon
and nitrogen oxide content in the exhaust fumes.
The carburettor needles on these carburettors are blocked with locking plugs.
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
adjustment 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.