Husqvarna 343R, 345RX, 343F, 345FX, 345FXT manual Carburettor settings, Function, Basic setting

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Fuel system 3

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 cylinder.

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, tempera- ture and air pressure.

L = Low speed needle H = High speed needle T = Idle adjustment screw

•The fuel quantity in relation to the air flow 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 anti- clockwise 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 recommended max. speed) and should be kept during the engine’s first working hours. Thereafter the carburettor should be fine tuned.

The default setting is:

H = 1 revolution open L = 1 revolution open

Fine adjustment

Fine adjustment of the carburettor should be carried out after the engine has been “run-in”.

•The air filter should be clean and the cylinder cover fitted when all adjustments are made.

First adjust the L-needle, then the H-needle and finally the idling speed’s T- screw.

Idling speed = 2,800 rpm.

•Since the ignition system is limited in terms of rpm, the pre-programmed fast idle speed (12,500 – 13,500 rpm) cannot be exceeded even if the H-needle is screwed inwards. The risk in this case is still that the engine breaks down as a result of a too lean fuel/air mix.

•At full throttle, the H-needle shall have a setting so that the engine is almost splutters.

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