Husqvarna K770 Workshop Manual page 40

come from the venturi, can the function of the needle
valve be examined as set out below.
6.6.8.3 Water test
To examine external leakage and the function of the
needle valve, lower the carburetor into water.
1. Connect a piece of hose to the pulse line. It must
come out above the water line.
2. Connect a thin, short hose from the pressure tester
to the fuel pipe of the carburetor.
3. Increase the pressure to 15–36 psi/100–2.5 bar.
The needle valve must lift and air bubbles come out of
the jets in the venturi. The pressure must then decrease
to approximately 15–7 psi/100–0.5 bar and then
decrease much slower or stop. A pressure drop after 7
psi/0.5 bar means there is a leak at the needle valve. If
the needle valve does not open at 36 psi/2.50 bar (max.
permitted pressure test) blow through the hole for filter
compensation (1) to open it. If the pressure does not
40 - Repair and servicing
increase, the cause can be a damaged pump
diaphragm.
6.6.8.4 To examine and clean the needle valve
Do a pressure test, refer to
test shows the needle valve has a leak, remove the
needle valve.
1. Examine the spring and make sure that the lever
runs easily on the axle.
2. Examine the needle end with a magnifying glass. If
there are signs of particles or if the end of the needle
is damaged, replace the needle.
1
Water test on page 40 . If the
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