Testing Automatic Choke; Leakage Testing Engine Housing And Control Valve - Stihl 029, 039 Service Manual

STIHL 029, 039
11.6.3

Testing Automatic Choke

- Remove the air filter –
see 11.1.1 or 11.1.2.
- Pull the terminal off the spark
plug. Unscrew the spark plug.
- Close the choke by moving the
Master Control down to the cold
start position.
- Open the choke shutter slowly by
turning the right-hand end of the
shaft.
Note: The throttle shutter must jump to
the idle position (almost closed) just
before the choke shutter is fully closed.
This is accompanied by a definite
clicking sound.
- Pull the starter rope slowly:
Depending on the temperature of
the control valve, you should
observe one of the following
functions:
Control valve temperature
above +35°C (95°F):
Choke shutter begins to open during
first revolution of crankshaft and
opens fully for brief moment after
second revolution of crankshaft.
Note: Pulling starter rope out about
40 cm (16") is equivalent to two
revolutions of crankshaft.
Control valve temperature
between +5°C (40°F) and +25°C
(77°F):
Choke shutter only begins to open
after several revolutions of crankshaft
and opens briefly to no more than 45
degrees when starter rope is fully
extended. It must not move to the fully
open position.
Control valve temperature
below -5°C (3°F):
Choke shutter must not move
while the starter rope is pulled
out to its full length.
11.6.4 Leakage Testing
Engine Housing and
Control Valve
Air inlet hose on bellows
It is necessary to interrupt the
connection between the automatic
choke and atmosphere before testing
the engine housing and built-in control
valve for leaks.
The connection between the cylinder
and control valve is also tested for
leaks during the pressure and vacuum
tests. The vacuum test is used to check
the complete control valve since only
part of the valve is pressurized in the
pressure test.
- Remove the air filter - see 11.1.
- Pull the air inlet hose off the nipple
on the bellows.
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