Stihl MS 251 Instruction Manual - Page 96

Adjusting the Carburetor, 12.7.1 Basic Setting, to 3, 300 rpm.

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12.7 Adjusting the Carburetor 12.7.1 Basic Setting The basic setting is necessary only if the high speed screw (H) or low speed screw (L) has to be replaced or after cleaning and adjusting the carburetor from scratch. It is necessary to carry out the basic setting after removing the limiter cap. The carburetor and air filter are installed, the adjusting screws fitted and the new limiter cap preinstalled. - Check chain tension and adjust if necessary. - Inspect the spark arresting screen (if fitted) and clean or replace if necessary, b 3.7 or b 6.1 - Check the air filter and clean or replace if necessary, b 12.1 1 2 : Starting with the low speed screw L (2) against its seat, open it 1 full turn counterclockwise - this is the basic setting. - Warm up the engine. The setting disc 5910 893 6600 may be fitted on the screwdriver 5910 890 2306 to aid adjustment. 1 2 : Insert the screwdriver (1) 5910 890 2306 through the opening (arrow) and into the low speed screw L and high speed screw H - push the screwdriver through the pre-installed limiter cap on the high speed screw H. Adjust idle speed with a tachometer. Adjust specified engine speeds within a tolerance of ± 200 rpm. 14 12 0 10 8 4 6 2310RA283 TG If this speed is higher than 3,700 rpm, abort the procedure and start again with step 1. 3. Use the idle speed screw (LA) to set the engine speed again to 3,300 rpm. 4. Use the low speed screw (L) to set engine speed to 2,800 rpm. 5. Use the high speed screw (H) to set the engine's maximum speed to 13,000 rpm. (starting with H = 1 1/2 turns open). As soon as a maximum engine speed of 13,000 rpm is obtained, do not attempt to make the mixture any leaner - the ignition module limits maximum engine speed to 13,000 rpm. This speed cannot be increased by making the setting leaner. Making the mixture overlean increases the risk of engine damage. 2310RA284 TG 1. Adjust engine speed with idle speed screw (LA), to 3,300 rpm. 2310RA282 TG For the sake of clarity the adjusting screws are shown on the exposed carburetor. : Starting with the high speed screw H (1) against its seat, open it 1 1/2 turns counterclockwise - this is the basic setting. 2. Turn the low speed screw (L) counterclockwise or clockwise to obtain maximum engine speed. : Insert a drift through the opening (arrow) and then push home the limiter cap until it engages. MS 231, MS 231 C, MS 251, MS 251 C 95

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95
MS 231, MS 231 C, MS 251, MS 251 C
12.7
Adjusting the Carburetor
12.7.1
Basic Setting
The basic setting is necessary only
if the high speed screw (
H
) or low
speed screw (
L
) has to be replaced
or after cleaning and adjusting the
carburetor from scratch.
It is necessary to carry out the basic
setting after removing the limiter
cap.
The carburetor and air filter are
installed, the adjusting screws fitted
and the new limiter cap pre-
installed.
–
Check chain tension and adjust if
necessary.
–
Inspect the spark arresting
screen (if fitted) and clean or
replace if necessary,
b
3.7 or
b
6.1
–
Check the air filter and clean or
replace if necessary,
b
12.1
For the sake of clarity the adjusting
screws are shown on the exposed
carburetor.
:
Starting with the high speed
screw
H
(1) against its seat,
open it
1 1/2 turns
counter-
clockwise – this is the basic
setting.
2310RA282 TG
1
2
:
Starting with the low speed screw
L
(2)
against its seat, open it
1 full turn
counterclockwise
– this is the basic setting.
–
Warm up the engine.
The setting disc 5910 893 6600
may be fitted on the screwdriver
5910 890 2306 to aid adjustment.
:
Insert the screwdriver (1)
5910 890 2306 through the
opening (arrow) and into the low
speed screw
L
and high speed
screw
H
– push the screwdriver through
the pre-installed limiter cap on
the high speed screw
H
.
Adjust idle speed with a tachometer.
Adjust specified engine speeds
within a tolerance of ± 200 rpm.
1.
Adjust engine speed with
idle speed screw (
LA
),
to 3,300 rpm.
2.
Turn the low speed screw (
L
)
counterclockwise or clockwise
to obtain maximum engine
speed.
0
14
12
10
8
6
4
2
0
14
12
10
2310RA283 TG
1
If this speed is higher than
3,700 rpm, abort the procedure and
start again with step 1.
3.
Use the idle speed screw (
LA
)
to set the engine speed again to
3,300 rpm.
4.
Use the low speed screw (
L
)
to set engine speed to
2,800 rpm.
5.
Use the high speed screw (
H
)
to set the engine's maximum
speed to 13,000 rpm.
(starting with H = 1 1/2 turns
open).
As soon as a maximum engine
speed of 13,000 rpm is obtained, do
not attempt to make the mixture any
leaner – the ignition module limits
maximum engine speed to 13,000
rpm. This speed cannot be
increased by making the setting
leaner. Making the mixture over-
lean increases the risk of engine
damage.
:
Insert a drift through the
opening (arrow) and then push
home the limiter cap until it
engages.
2310RA284 TG