Heating System; Carburetor Heating; Testing The Complete System; Testing The Heating Element - Stihl MS 661 Manual

14.

Heating System

14.1

Carburetor Heating

The heating element is installed
between the filter base and the
carburetor. Current is supplied via a
wire to the heating element.
The heating element is controlled by
a thermostatic switch on the
underside of the carburetor.
The heating element and
thermostatic switch should be
checked if running problems occur
when the cold engine is idling or
running at part load, particularly at
temperatures below freezing.
Idling problems with a hot engine
are also an indication of a fault in the
heating element or thermostatic
switch.
14.1.1 Testing the 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).
– Test the heating system as
specified in the carburetor
heating troubleshooting chart,
b 14.2
– Remove the air filter, b 13.1
– Set the ohmmeter to measuring
range "Ω".
118
: Clip one of the two test leads to a
nut on the filter base and the
other to a cylinder fin.
If the system is in good condition the
ohmmeter will indicate a value
of about 10 Ω in measuring range
"Ω".
If the reading obtained is outside
this tolerance, test each component
separately.
14.1.2 Testing the Heating
Element
– Remove the filter base, b 13.3
3
1
: Pull the wire (1) out of the guides
and disconnect the flag
terminal (2).
: Take the heating element (3) off
the studs.
: Clip one test lead to the heating
element and the other to the
spade terminal.
If the heating element is in good
condition the ohmmeter will indicate
a value of about 8 Ω in measuring
range "Ω".
Installing
1 2
: Fit the heating element (1) over
2
the studs so that the wire (2) is at
the top right.
: Hold the flag terminal (3) with the
crimped side facing the
carburetor and push it fully onto
the connector tag (arrow).
MS 661, MS 661 C-M
3