PIAGGIO 633929(IT), Service Station Manual, Page: 158 / 314

Inspecting the cut-off
- Remove the SAS valve
- Connect the MITYVAC pump in depression mode
(VACUUM) to the depression valve socket CUT -
OFF
- Apply a vacuum value higher than 0.5 BAR
- Check that this value is kept at all times
- 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 depression uptake of the CUT-OFF valve.
- Connect the bypass to the MITYVAC pump
- Set the pump set to the depression position
(VACUUM)
- Using a pair of long flat pliers, pinch the rubber
hose next to the valve
- Operate the pump until a vacuum higher than 0.5
BAR is created
- Release the hose and check how the vacuum re-
acts
- Under normal functioning the vacuum undergoes
a slight fall and then readjusts. There follows a
slow and continuous loss of depression up to ap-
proximately 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). INCORRECT CUT-OFF
VALVE CALIBRATION CAN RESULT IN CATA-
LYTIC CONVERTER MALFUNCTION.
N.B.
A FAULTY CUT - OFF VALVE DIAPHRAGM,
BESIDES JEOPARDISING THE CORRECT OP-
ERATION OF THE CUT-OFF VALVE, ALSO
DAMAGES IDLE FUNCTIONING.
Specific tooling
Engine
MP3 125
ENG - 64