Stihl FC 90 Product Instruction Manual - Page 24

Fine Tuning

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English N Carefully turn both adjusting screws counterclockwise as far as stop: - The high speed screw (H) is 3/4 turn open. - The low speed screw (L) is 3/4 turn open. N Start and warm up the engine. N Adjust idle speed with the idle speed screw (LA) so that the cutting blade does not rotate. Fine Tuning 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. Rule of thumb: Turn the high speed screw (H) about one quarter of a turn for every 3300 ft (1000 m) change in altitude. 249BA051 KN Conditions for adjustment N Carry out the standard setting without disturbing the high speed screw (H). 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. Readjust idle 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 cutting blade must not rotate. Blade rotates when engine is idling N Turn the idle speed screw (LA) counterclockwise until the cutting blade stops rotating and then turn the screw about another 1/2 to 3/4 turn in the same direction. If the cutting blade continues to rotate when the engine is idling, have your machine 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. 22 FC 90

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FC 90
English
22
N
Carefully turn both adjusting screws
counterclockwise as far as stop:
–
The high speed screw
(H) is 3/4 turn
open.
–
The low speed screw (L) is 3/4 turn
open.
N
Start and warm up the engine.
N
Adjust idle speed with the idle speed
screw (LA) so that the cutting blade
does not rotate.
Fine Tuning
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.
Rule of thumb:
Turn the high speed screw (H) about
one quarter of a turn for every 3300 ft
(1000 m) change in altitude.
Conditions for adjustment
N
Carry out the standard setting
without disturbing the high speed
screw (H).
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.
Readjust idle
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 cutting blade
must not rotate.
Blade rotates when engine is idling
N
Turn the idle speed screw (LA)
counterclockwise until the cutting
blade stops rotating and then turn
the screw about another 1/2 to 3/4
turn in the same direction.
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.
249BA051 KN
If the cutting blade continues to
rotate when the engine is idling,
have your machine checked and
repaired by your servicing dealer.