34 TS 410, TS 420
7.2 Leak testing
Defective oil seals and gaskets or
cracks in housing are the usual
causes of leaks. Such faults allow
supplementary air to enter the
engine and upset the fuel-air
mixture.
This makes adjustment of the
prescribed idle speed difficult, if not
impossible.
Moreover, the transition from idle
speed to part or full throttle is not
smooth.
Always start with the vacuum test
and then continue with the pressure
test.
The shortblock can be thoroughly
checked for leaks under vacuum
and at gauge pressure using the
pump 0000 850 1300.
7.2.1 Preparatory steps
– Remove the shroud, b 7.4.
The spark plug (2) must be screwed
tight.
370RA089 TG
2
1
– Remove the decompression
valve, b 7.9.
: Fit the plug (1) 4221 025 2200
and screw it tight.
– Tightening torques, b 3.5.
: Undo the screws (arrows).
: Fit a sealing plate (1)
0000 855 8106 between the
cylinder exhaust port and cooling
plate, then tighten the screws
down gently.
The sealing plate must fill the full
width between the screws.
– Remove the carburetor, b 12.2.
370RA057 TG
1
370RA090 TG
: Slide a flange 4238 890 1200 (1)
between tank housing and
manifold.
– Adjust the flange: the holes in the
manifold, flange and tank
housing must be lined up.
: Insert and tighten down the
M5x48 screws (arrows).
7.2.2 Vacuum test
Oil seals tend to fail when subjected
to a vacuum. In other words, the
sealing lip lifts away from the
crankshaft during the piston's
induction stroke because there is no
internal counterpressure.
This kind of fault can be detected by
testing with pump 0000 850 1300.
1
370RA091 TG370RA092 TG
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