Spark Plug - Stihl SP 451 Instruction Manual

N Turn the high speed screw (H)
about one eighth of a turn for every
1000m change in altitude.
N Carry out standard setting on low
speed screw (L).
N Warm up the engine for about 3
minutes.
N Open the throttle wide.
At high altitude
N Turn the high speed screw (H)
clockwise (leaner), no further than
stop, until there is no further
noticeable increase in engine
speed.
At sea level
N
Turn the high speed screw (H)
counterclockwise (richer), no further
than stop, until there is no further
noticeable increase in engine
speed.
It is possible that maximum engine
speed may be reached with the standard
setting in each case.
Adjusting Idle Speed
It is usually necessary to change the
setting of the idle speed screw (LA) after
every correction to the low speed
screw (L).
N Warm up the engine for about 3
minutes.
Engine stops while idling
N Turn the idle speed screw (LA)
slowly clockwise until the engine
runs smoothly – the hook must not
move.
SP 451, SP 481
Hook runs when engine is idling
N Turn the idle speed screw (LA)
counterclockwise until the hook
stops moving and then rotate the
screw another 1/2 to 1 turn in the
same direction.
If the hook continues moving
when the engine is idling, have
your power tool checked and
repaired by your servicing dealer.
Erratic idling behavior, engine stops
even though setting of LA-screw has
been corrected, poor acceleration
Idle setting is too lean
N Turn the low speed screw (L)
counterclockwise, no further than
stop, until the engine runs and
accelerates smoothly.
Erratic idling behavior
Idle setting is too rich
N
Turn the low speed screw (L)
clockwise, no further than stop, until
the engine runs and accelerates
smoothly.

Spark Plug

N
If the engine is down on power,
difficult to start or runs poorly at idle
speed, first check the spark plug.
N Fit a new spark plug after about 100
operating hours – or sooner if the
electrodes are badly eroded. Install
only suppressed spark plugs of the
type approved by STIHL – see
"Specifications".
Removing the spark plug
N Move the slide control to STOP-0
(h).
N Pull off the spark plug boot (1).
N Unscrew the spark plug.
English
17