Husqvarna 340, 345, 346XP,350, 351, 353 manual Construction and function, Carburettor

Construction and function

Carburettor

The carburettor consists of three sub-systems:

•The metering unit (A) which contains the jets and the fuel control mechanism. This measures out the right amount of fuel to suit the speed of the saw and the power demand.

•The mixing unit (B) consists of the choke, diffuser jets and throttle valve. This is where the air and fuel are mixed to create a flammable mixture.

•The pump unit (C) pumps fuel from the tank to the metering system inside the carburettor. One side of the pump diaphragm is connected to the crankcase and pulses as a result of pressure changes in the crankcase. The other side of the diaphragm sucks in the fuel.

The carburettor works in different ways depending on the setting:

•Cold start mode

•Idling mode

•Part throttle mode

•Full throttle mode

In the cold start mode the choke valve (D) is completely closed. This increases the vacuum in the carburettor so that fuel is sucked through the diffuser jets faster (E).

In idling mode the throttle valve (F) is closed. Air is sucked through an aperture in the throttle valve and a small amount of fuel is supplied through the diffuser jet (E).

8 – English