Stihl MS 650

91MS 650, MS 660
Complete system
The generator and heating element
are checked in the following test
which should be performed at an
ambient temperature of at least
+20°C (68°F).
If the temperature is lower than
+ 13 °C (55 °F), the thermostatic
switch may close and produce false
readings.
Test the thermostatic switch
separately.
– Remove filter base –b 12.1
– Set the ohmmeter to measuring
range “Ω“.
: Clip one of the two test leads to
the carburetor body and the other
to a cylinder fin (ground).
– If the system is in good condition
the ohmmeter will indicate about
8 Ω in measuring range "Ω".
VA
176RA314
100
50
30
20
10
5
0
20
10
5
3
1
To ensure good electrical contact,
press the heating plate and the
heating element against the
carburetor during the
measurement.
If the reading obtained is outside
this tolerance, test each component
separately.
: Remove the wires from the
retainer (arrow).
: Push back the insulating tubes
(1) and disconnect the pin and
socket connectors.
178RA176
VA
1
Thermostatic switch
– Remove the heating element.
: Clip test leads to the heating
element’s connectors.
178RA177
VA
At temperatures above + 20 °C
(68 °F), the ohmmeter must indicate
an infinitely high value in measuring
range “Ω“.
Cool the switch down to below
+ 6 °C (42 °F). The ohmmeter must
indicate a value of about 8 Ω in
measuring range “Ω“. If a higher
value is indicated, install a new
heating element.
13.1 Testing