Stihl BT 121 Instruction Manual page 17

L
H
1
LA
N Turn high speed screw (H)
counterclockwise as far as stop (no
more than 3/4 turn).
N Turn the low speed screw (L)
carefully clockwise until it is against
its seat, then turn it back 1 full turn.
N Start and warm up the engine.
N Adjust idle speed with the idle speed
screw (LA) so that the drilling
spindle does not rotate.
Adjusting Idle Speed
Engine stops while idling
N Carry out standard setting on low
speed screw (L).
N Turn the idle speed screw (LA)
slowly clockwise until the engine
runs smoothly – the drilling spindle
must not rotate.
BT 121
Drilling spindle rotates when engine
is idling
N Turn the idle speed screw (LA)
counterclockwise until the drilling
spindle stops rotating and then turn
the screw another 1/2 to 1 turn in the
same direction from that position.
Erratic idling behavior, poor
acceleration (even though low speed
screw is open one turn)
Idle setting is too lean.
N Turn the low speed screw (L) slowly
counterclockwise until the engine
runs and accelerates smoothly.
It is usually necessary to change the
setting of the idle speed screw (LA) after
every correction to the low speed
screw (L).
Fine Tuning for Operation in
Mountains or at Sea Level
A slight correction of the setting of the
high speed screw (H) may be necessary
if engine power is not satisfactory when
operating at high altitude or at sea level.
N Check the standard setting.
N Warm up the engine.
N Adjust idle speed properly.
At high altitude
N
Turn high speed screw (H)
clockwise (leaner) – no further than
stop.
At sea level
N Turn high speed screw (H)
counterclockwise (richer) – no
further than stop.
If the setting is too lean there is a
risk of engine damage due to
insufficient lubrication and
overheating.
English
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