Operation Manual

21BR 420
English / USA
Standard Setting
: Shut off the engine.
: Check the air filter and clean or
replace if necessary.
: Check the spark arresting screen (if
fitted) in the muffler and clean or
replace if necessary.
: Carefuly turn both adjusting screws
counterclockwise as far as stop:
High speed screw (H) is now open
1/4 turn
Low speed screw (L) is now open
1/4 turn
: Start and warm up the engine.
Adjusting Idle Speed
Engine stops while idling
: Turn the idle speed screw (LA)
clockwise until the engine runs
smoothly.
Erratic idling behavior, engine stalls
even after re-adjusting LA screw,
poor acceleration
Idle setting is too lean:
: Turn low speed screw (L)
counterclockwise – no further than
stop – until the engine runs and
accelerates smoothly.
Erratic idling behavior
Idle setting is too rich:
: Turn low speed screw (L) clockwise
– no further than stop – until the
engine runs and still 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 engine power is not
satisfactory:
: Check standard setting.
: Warm up the engine.
: Turn the high speed screw (H)
clockwise (leaner) – no further than
stop.
If the setting is too lean, there is a
risk of engine damage due to
insufficient lubrication and
overheating.
H
L
373BA043 KN
LA
L
373BA044 KN