Stihl MS 440 Service Manual

79MS 440, MS 440 C
Current is supplied via wires to the
heating element installed between
the baffle and the carburetor.
Carburetor heating is controlled by
a thermostatic switch on the heating
element
The carburetor heating system
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
carburetor heating system.
Checking correct operation of the
complete system
The generator and heating element
are tested when checking correct
operation of the complete system.
An ambient temperature of at least
+20 °C (68 °F) is required for this
purpose.
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 the 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).
VA
176RA314
100
50
30
20
10
5
0
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5
3
1
– If the system is in good condition
the ohmmeter will indicate about
8 Ω in measuring range "Ω".
If the reading obtained is outside
this tolerance, test each component
separately.
Heating element
– Disconnect the lead to the
heating element.
: Clip one test lead to the heating
plate, the other to the wire that
goes to the heating element.
100
50
30
20
10
5
0
20
10
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1
VA
176RA315
– If the heating element is in good
condition the ohmmeter will show
a reading of about 8 Ω in
measuring range "Ω".
If the reading obtained is outside
this tolerance, install a new heating
element.
Thermostatic switch
– Disconnect the lead to the
thermostatic switch.
: Clip one test lead to the heating
plate, the other to the wire that
goes to the thermostatic switch.
At temperatures above + 20 °C
(68 °F), the ohmmeter must indicate
an infinitely high value in measuring
range "Ω".
100
50
30
20
10
5
0
20
10
5
3
1
VA
176RA316
Cool the switch to below +6 °C
(42 °F). The ohmmeter must
indicate a value of 0.5 Ω in the "Ω"
range. If not, the thermostatic switch
is defective and must be replaced.
13. Carburetor Heating

Stihl MS 440 Specifications

General

Displacement	70.7 cc
Chain Pitch	3/8"
Ignition system	Electronic
Starter	Recoil starter
Vibration reduction	Anti-vibration system
Weight (without bar and chain)	6.4 kg
Fuel tank volume	0.73 L
Oil Capacity	0.36 L
Guide Bar Length	40-63 cm
Guide Bar Length (recommended)	40-71 cm (16-28 in)