Husqvarna 555 XP Workshop Manual page 35

Function
The carburettor operates differently in the following
modes:
• Cold start mode
• Idling mode
• Part throttle mode
• Full throttle mode
In cold start mode the choke valve H is completely
shut. This increases the vacuum in the carburettor
and fuel is easier to suck from all the diffuser jets
D, E, and F. The throttle valve I is partly open. The
throttle valve, J, is closed. See figure 30.
In idling mode, the throttle valves I and J are
closed and the choke valve H is open.
Air is sucked in through an aperture in the throttle
valve and a small amount of fuel is supplied
through the diffuser jet D. See figure 31.
In part throttle mode, the throttle valve I is partly
open and the choke valve H is fully open. Fuel is
supplied through the diffuser jets D and E. The
throttle valve, J, starts to open. See figure 32.
In the full throttle mode both valves are open and
fuel is supplied through all four diffuser jets (D, E,
F and G). The throttle valve, J, is fully open. See
figure 32.
Fig 30
Fig 31
Fig 32
Fig 33
Repair Instructions
35
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