BR 450, BR 450 C
English
21
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.
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 at High 
Altitude
A slight correction of the setting may be 
necessary if the engine does not run 
satisfactorily:
N Carry out the standard setting.
N Warm up the engine.
N Turn high speed screw (H) slightly 
clockwise (leaner) – no further than 
stop.
NOTICE
After returning from high altitude, reset 
the carburetor to the standard setting.
If the setting is too lean there is a risk of 
engine damage due to insufficient 
lubrication and overheating.
If there is a loss of engine power, the 
machine is difficult to start or runs poorly 
at idle, first check the spark plug.
Install a new spark plug after approx. 
100 operating hours or earlier if the 
electrodes are eroded/corroded.
The wrong fuel mix (too much engine oil 
in the gasoline), a dirty air filter and 
unfavorable running conditions (mostly 
at part throttle etc.) affect the condition 
of the spark plug. These factors cause 
deposits to form on the insulator nose, 
which may degrade performance.
Removing the spark plug
N Pull off the spark plug boot (1) 
vertically.
N Unscrew the spark plug (2).
Checking the Spark Plug
N Clean dirty spark plug.
N Check electrode gap (A) and 
readjust if necessary – see chapter 
"Specifications."
N Use only resistor type spark plugs of 
the approved range.
Rectify problems which have caused 
fouling of spark plug:
– too much oil in fuel mix,
– dirty air filter,
– unfavorable running conditions, e.g. 
operating at part load.
Spark Plug