Husqvarna 455 manual Maintenance, General, Carburetor adjustment, L H T, Function, Fine adjustment

MAINTENANCE

General

The user must only carry out the maintenance and service work described in this manual. More extensive work must be carried out by an authorised service workshop.

Carburetor adjustment

Due to existing environmental and emissions legislation your chain saw is equipped with movement limiters on the carburetor adjuster screws. These limit the adjustment possibilities to a maximum of a 1/2 turn.

1/2

1/2

Your Husqvarna product has been designed and manufactured to specifications that reduce harmful emissions.

Function

•The carburetor governs the engine’s speed via the throttle control. Air and fuel are mixed in the carburetor. The air/ fuel mixture is adjustable. Correct adjustment is essential to get the best performance from the machine.

•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 controls:

-L = Low speed jet

-H = High speed jet

-T = Idle adjustment screw

L

H

T

•The L and H-jets are used to adjust the supply of fuel to match the rate that air is admitted, which is controlled with the throttle. 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 lean mixture gives a higher engine speed and a rich mixture gives a lower engine speed.

•The T-screw regulates the throttle setting at idle speed. If the T-screw is turned clockwise this gives a higher idle speed; turning it anti-clockwise gives a lower idle speed.

Basic settings and running in

The basic carburetor settings are adjusted during testing at the factory. Avoid running at a too high speed for extended periods during the first 10 hours.

CAUTION! If the chain rotates while idling the T-screw must be turned anti-clockwise until the chain stops.

Rec. idle speed: 2700 rpm

Fine adjustment

When the machine has been ”run-in” the carburetor should be finely adjusted. The fine adjustment should be carried out by a qualified person. First adjust the L-jet, then the idling screw T and then the H-jet.

Conditions

•Before any adjustments are made the air filter should be clean and the cylinder cover fitted. Adjusting the carburetor while a dirty air filter is in use will result in a leaner mixture next time the filter is cleaned. This can give rise to serious engine damage.

•Do not attempt to adjust the L and H jets beyond either stop as this could cause damage.

•Now start the machine according to the starting instructions and let it warm up for 10 minutes.

•Place the machine 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 jet L

Turn the low speed jet L clockwise until it stops. If the engine accelerates poorly or idles unevenly, turn the low speed jet L anticlockwise until good acceleration and idling are achieved.

Fine adjustment of the idling speed T

Adjust the idle speed with the T-screw. If it is necessary to re- adjust, turn the T-screw clockwise while the engine is running, 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 chain saw until it has been properly adjusted or repaired.

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