Husqvarna K770 Workshop Manual page 35

Make a note of the connection of the link rod.
• Remove the 2 screws.
6.6.8 Needle valve
6.6.8.1 Indications of a needle valve leak
There are many symptoms of a needle valve with a leak.
A product that is used for short periods is usually not
easy to start when it is warm. Fuel leaks into the venturi
and gives too much fuel for the next warm start.
With a cold start, the fuel chamber above the needle
valve is dry. This is the situation especially when the
product has not been used for a long period. After trying
to start many times, new fuel has gone into the
carburetor and the product starts.
6.6.8.2 Test conditions
The best test result is from a carburetor that is drained,
but has some fuel left. Do not examine a fully dry
carburetor, or a carburetor that has not been used for a
long time. The result will not be accurate. When the
carburetor is full, turn the carburetor with the pulse line
up, as shown in the picture. Pump up the pressure to
approximately 30 psi/2 bar. Let the fuel run out through
the venturi which is fully in water. Not until air bubbles
651 - 001 - 27.06.2018
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
Repair and servicing - 35