Technical Information · issue 46 of 2003
FS 480 (new version); Carburetor C1Q-S94, Shroud, Grommet, Carburetor Housing; Support frame / powerhead (FR 450); Summary
IssueTI 46/2003
Part changes (1)
| Was | Becomes | What the bulletin says |
|---|---|---|
| 4128 120 0651 | 4128 120 0603 | 1 Carburetor The existing carburetor 4128 120 0651 (C1Q-S34H) with a single adjusting screw (LD) has been replaced by version 4128 120 0603 (C1Q-S94) with three adjusting screws (H, L, LA). |
Full text
Page 1 of 5
STIH)
Technical Information
46.2003
STIHL FS 450 Clearing Saws – Series 4128
Contents
1. Carburetor C1Q-S94, Shroud, Grommet, Carburetor Housing
2. Summary
1. Carburetor C1Q-S94, Shroud, The high speed adjusting screw on the new
Grommet, Carburetor Housing carburetor is equipped with a cap (1) to limit the
adjustment range. Funnel-shaped caps (2 and 3)
The modifications outlined below have been are also fitted to the low speed adjusting screw and
designed to further improve operation and adapt to the idle speed adjusting screw, as a guide to
emission standards. inserting the carburetor screwdriver.
1.1 Carburetor
The existing carburetor 4128 120 0651 (C1Q-S34H)
with a single adjusting screw (LD) has been
replaced by version 4128 120 0603 (C1Q-S94) with
three adjusting screws (H, L, LA).
270°
1 2
256TI022 KN
LD H
With the new carburetor, the user can only adjust
3 the high speed adjusting screw H within a range of
270° (3/4 turn).
256TI021 KN
In this way, the carburetor setting can be adjusted to
LA
different working conditions (e.g. change of
altitude).
Left: existing carburetor C1Q-S34H
Right: new carburetor C1Q-S94
TI_46_2003_02_01_01.fm englisch / English USA
)m~ge 2 Technical Information 46.2003
1.1.1 Mechanical design Adjustment after maintenance / repair
. Check the air filter – clean or replace if
necessary
. Check the muffler / spark arresting screen for
5 coking and clean or replace if necessary
. Check throttle cable setting and adjust if
1 2
necessary
3
. Inspect the fuel filter and clean or replace if
necessary.
256TI023 KN
4
Basic setting (Service)
(without cap on high-speed adjusting screw)
. Low speed adjusting screw (1)
. High speed adjusting screw (2)
. Cap (3) of high speed adjusting screw
H L
. Idle speed adjusting screw (4)
. Stop (5) to limit the range of travel of the high
speed adjusting screw cap
1.1.2 Maintenance / repair (Service)
256TI025 KN
Starting from the tight position of the adjusting
screws:
. Back off H = 1 1/2 turns
. Back off L = 1 turn
Fixing cap on H screw
256TI024 KN
1 2
The high speed adjusting screw cap must be
removed in order to replace a high speed adjusting
screw or to clean the carburetor.
. Insert the extractor 5910 890 4501 (1) between
the cap (2) and the carburetor housing as
shown
256TI026 KN
. Pry off the cap –
if the cap binds on the adjusting screw:
. Fit a new cap facing towards the rich stop
. Turn the extractor so that the closed side of the
(arrow) and press on until it is engaged in
U-shaped blade is facing the cap and slide the
position 2
extractor under the cap
. Pry off the cap fully
Caps must not be reused
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Technical Information 46.2003 Page 3
. Check the muffler / spark arresting screen for
a coking and clean or replace if necessary
. Check the throttle cable adjustment and adjust if
necessary
. Turn the high speed adjusting screw (H)
counterclockwise as far as possible – max. 3/4
turn
. Carefully turn the low speed adjusting screw (L)
clockwise lightly against the seat, then back off
256TI027 KN
1 turn
. Start the machine and let the engine warm up
Do not press on the cap all the way to the carburetor
. Adjust the idle speed by means of the idle speed
housing, as this will damage it!
adjusting screw (LA) so that the cutting tool
Distance a = 1 mm
does not turn
Engine stops when idling
Idle speed adjustment
. Carry out standard setting procedure on low
. Turn the idle speed adjusting screw (LA) to set speed adjusting screw (L)
the speed to 2800 rpm (a tachometer should be
. Turn the idle speed adjusting screw (LA)
used as an aid to adjustment!)
Checking running behaviour
clockwise until the engine runs evenly. The
cutting tool should not turn
Speed varies when idling, poor acceleration, The attachment turns when idling
engine stops –
. Turn the idle speed adjusting screw (LA)
the idle setting is too lean!
counterclockwise until the attachment stops,
. Turn the low speed adjusting screw (L) then turn approx. 1/2 to 1 more turn in the same
counterclockwise about 1/4 turn until the engine direction
runs uniformly and accelerates correctly
Adjusting the carburetor setting when working
Speed varies when idling; engine stops when in mountain regions
swivelling machine –
If the engine does not run satisfactorily, a marginal
the idle setting is too rich!
adjustment may be necessary:
. Turn the low speed adjusting screw (L)
. Check the standard setting
clockwise about 1/4 turn until the engine runs
uniformly and accelerates correctly . Let the engine warm up
Whenever the low speed adjusting screw (L) has . Turn the high speed adjusting screw (H)
been adjusted, an adjustment is usually required on clockwise (leaner)
the idle speed adjusting screw (LA)
1.1.4 Spare parts
Set of carburetor parts 1129 007 1062 should be
1.1.3 Standard setting used for repairs to the new carburetor.
(with cap on high speed adjusting screw)
The instructions below correspond to the
instructions for adjustment in the "Carburetor
adjustment" chapter of the machine operator’s
manual.
. Switch off the engine
. Fit the cutting tool
. Check the air filter and clean or replace if
necessary
TI_46_2003_02_01_01.fm
)m~ge 4 Technical Information 46.2003
1.2 Shroud, grommet, carburetor housing
256TI028 KN
256TI029 KN
Left: existing shroud (with opening for grommet) Left: existing carburetor housing
Right: new shroud (with 3 adjustment openings) Right: new carburetor housing
Modified shrouds (without an opening in the area of The integrally molded holders (arrows) for the
the carburetor adjusting screws) have been grommet are not used on the new carburetor
installed along with the introduction of the new housing. The collar screws for attaching the
carburetor. carburetor are injection-molded instead of screwed.
The new adjustment symbols (H=3/4; L=1; LA) are
The bushing in the mounting hole is injection-
molded and not a press-fit. Consequently, these
now shown on the shroud, adjacent to the
parts cannot be individually replaced on new
3 adjustment openings (previously on the
grommet). carburetor housings.
Supply of spare parts
Due to the funnel-shaped caps on the adjusting
screws on the new carburetor, the grommet The carburetor housings (4128 120 0101 and
previously used in the carburetor housing is no 4128 120 0100) still available for machines with the
longer required. old-style carburetor are also supplied with injection-
molded collar screws and bushings. The collar
screws 4134 122 6601 and bushings
0000 963 1403 are still available for repairs to older
carburetor housings.
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Technical Information 46.2003 Page 5
2. Summary
Part name Previous New Remarks
FS 450
1 Carburetor C1Q-S34H 4128 120 0651 --- 1)
2 Carburetor C1Q-S94 --- 4128 120 0603 2)
3 Carburetor housing 4128 120 0101 4128 120 0102 1)
4 Grommet 4128 123 7502 --- 1)
5 Set of carburetor parts --- 1129 007 1062 2)
6 Shroud, USA 4128 080 1651 4128 084 0908 1)
Modification to be introduced continuously
Remarks
1) Previous version of part remains available for older machines
2) The spare parts are listed in the current spare parts list
Last Technical Information on the STIHL FS 450: 05.2003
© ANDREAS STIHL AG & Co. KG, 2003 Technical Documentation
D1/MTK-sc 7979
TI_46_2003_02_01_01.fm Page 4 of 5
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Extracted from the manufacturer's 2012 service catalogue. Most of these PDFs embed fonts with a shifted character map, so the text above was recovered rather than copied — read it as a faithful but imperfect transcription, and treat the page image above each block as the authority where the two disagree — the figures exist only there, because they are vector drawings that text extraction cannot keep.