Inspecting the cut-off
- Remove the SAS valve.
- Connect the MITYVAC pump in low-pressure
mode (VACUUM) to the CUT-OFF valve vacuum
intake.
- Apply a vacuum value higher than 0.5 BAR.
- Check that this value is kept all the time.
- If a worn seal is detected, replace it.
- With a "T" bypass and flexible rubber hoses make
a parallel connection between the rubber coupling
and the vacuum intake of the CUT-OFF valve.
- Connect the bypass to the MITYVAC pump.
- Set the pump set to the low-pressure mode
(VACUUM).
- Using a pair of long flat pliers, choke the rubber
hose next to the valve.
- Operate the pump until vacuum is higher than 0.5
BAR.
- Release the hose and check how the vacuum re-
acts. - Under normal functioning conditions the
vacuum undergoes a slight fall and then readjusts.
There follows a slow and continuous loss of de-
pression up to approximately 0.4 BAR. At this point
the valve opens and the depression is suddenly
set to zero.
Lack of tightness or the fact that the valve opens
at different vacuum values should be regarded as
anomalies. In this case, replace it.
N.B.
LACK OF TIGHTNESS IN THE CUT-OFF VALVE RESULTS
IN EXHAUST NOISE (EXPLOSIONS IN THE MUFFLER). IN-
CORRECT CUT-OFF VALVE CALIBRATION CAN RESULT
IN CATALYTIC CONVERTER MALFUNCTIONING
N.B.
A FAULTY CUT-OFF VALVE DIAPHRAGM, BESIDES
JEOPARDISING THE CORRECT OPERATION OF THE
CUT-OFF VALVE, ALSO DAMAGES IDLE FUNCTIONING
Specific tooling
020329Y MityVac vacuum-operated pump
Engine Vespa GT 125-200
ENG - 164
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