Husqvarna 390XP Workshop Manual page 43

4. That the piston ring is not burnt into its groove.
5. Measure the wear on the piston ring by placing it in
the cylinder and measuring the gap. See figure 4.
The gap must not exceed 1 mm.
6. That the needle bearing is undamaged.
7. That the intake manifold and it's rubber seals are
undamaged
8. Pressure test the decompression valve.
A. Connect the pressure testing device (Refer to pos
3 "3 Service tools" on page 8) to the decompres-
sion valve.
B. Pressurize to 80 kPa (0.8 bar).
C. Wait 30 seconds.
D. The pressure must not fall below 60 kPa (0.6 bar).
Faults and causes
Score marks on the piston. See Figure 6.
1. Incorrect carburettor setting. Too high over-speed.
2. Too low octane fuel.
3. Too low or incorrect oil in the fuel.
Carbon build-up. See Figure 7.
1. Incorrect carburettor setting. Too low over-speed.
2. Too much or incorrect oil in the fuel.
Piston ring breakage
1. Excessive engine speed.
2. Piston ring worn out.
3. Oversized piston ring groove.
Max. 1 mm
Fig. 4
Fig. 4
Fig. 5
Fig. 5
Fig. 6
Fig. 6
A B
Fig. 7
Fig. 7
Piston and cylinder
A B
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