Stihl 064 Service Manual page 87

STIHL 064, 066
- Run engine at a full throttle and
slowly rotate high speed adjust-
ing clockwise until tachometer
indicates 12,000 rpm.
- Allow engine to return to idle
speed.
- Rotate high speed adjusting
screw another half turn clockwise.
Note: This is the optimum setting
of the high speed adjusting screw
under the barometric pressure and
climatic conditions at the operating
site.
With the carburetor adjusted in
this way the engine speed at full
throttle may reach the cut-off
range of the governor. As the
tachometer uses the firing pulse
to measure engine speed, it can,
at full throttle, indicate a speed
which is much lower than the true
maximum rpm. This is due to the
fact that the engine does not fire
on every revolution when it is
running within the operating range
of the electronic speed governor.
Note (064 only): If the amount of
adjustment travel left on the high
speed adjusting screw, after set-
ting it to 12,000 rpm, is much less
than one half turn, the fixed jet
"64" can be installed in place of
fixed jet "68" - see 11.5.
Corrections to high speed ad-
justing screw with LED (066)
- Adjust idle speed correctly.
- Carefully screw the high speed
adjusting screw down onto its
seat.
- From this position, back off the
high speed adjusting screw exact
ly two full turns.
- Start the engine and allow it to
warm up.
- Run engine at a full throttle and
slowly rotate high speed adjust-
ing clockwise until the LED lights
up.
- Allow engine to return to idle
speed.
- Rotate high speed adjusting
screw another half turn clockwise.
Note: This adjustment can be car-
ried out with a tachometer if the
LED fails.
11.8 Tank Vent
Prying vent connector off stub
Correct operation of the carburetor
is only possible if atmospheric
pressure and internal fuel tank
pressure are equal at all times.
This is ensured by the tank vent.
Important: In the event of trouble
with the carburetor or the fuel sup
ply system, always check and
clean the tank vent.
- Remove the air filter - see 11.1.
- Remove the vent connector from
the stub on the tank housing.
- Pull the vent hose out of the bore
in the carburetor box.
87