Technical Information · issue 21 of 1999
FC 75, FH 75, HL 75, 75 K, HT 70, 75, FS 75, 80, 85, FR 85: Uprated Engine
IssueTI 21/1999
Full text
Page 1 of 8
Technical Information
21.1999
STIHL FH 75 Power Scythe - Series 4230
STIHL HL 75, 75 K Hedge Trimmers - Series 4230
STIHL HT 70, 75 Pole Pruners - Series 4138
STIHL FC 75 Power Edger - Series 4137
STIHL FS 75, 80, 85 Brushcutters - Series 4137
Contents
1. Uprated Engine
1.1 Filter housing
1.2 Carburetor
1.3 Spacer flange
1.4 Shroud
1.5 Service notes
1.6 Summary
1. Uprated Engine
Refer to “1.5 Service notes” when replacing parts
and assemblies.
4
1.1 Filter housing
2
5 5
1
3
392TI021 KN
392TI000 KN
2 2
Left: Previous version
Right: New version
As a result of optimization of the engine a new
carburetor (1) with a different idle system and new,
modified versions of the filter housing (2), spacer The new versions of the filter housing (2) and choke
flange (3) and shroud (4) will be installed from serial shutter (5) are shaped to provide an increased air
number 1 42 812 154 in place of the original flow volume.
versions. The modifications carried out on the
The new filter housing can be identified by the
engine resulted in an increase in power from 0.9 kW
recesses (arrows) which allow easier removal of the
(1.2 bhp) to 0.95 kW (1.3 bhp)
felt filter element without the need for tools.
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)m~ge 2 Technical Information 21.1999
The new choke shutter (5) has a smoother surface Outlet valve (new)
structure and is wider than the previous version.
1.2 Carburetor A B C
392TI023 KN
L LD Left: C1Q-S41 previous version
Right: C1Q-S45 new version
A = Valve jet with integral fixed jet
B = Outlet valve
392TI022 KN
LA C = Fixed jet
Carburetor adjusting screws Original and new carburetors differ in terms of the
Left: C1Q-S41 previous version construction of the valve jet.
Right: C1Q-S45 new version
In valve jet (A), the fixed jet is an inseparable part of
the component.
The original C1Q-S41 carburetor with external idle By contrast, the fixed jet (C) is screwed into the
speed screw LA will be replaced by the new outlet valve (B) on the new BIS carburetor and
C1Q-S45 with integral idle speed screw LD and makes servicing work much easier.
balanced idle system (BIS).
The diameter of the venturi on the new carburetor is
about 1 mm larger than the previous version.
The benefits, construction and function of the 1.3 Spacer flange
carburetor with a balanced idle system are
described in detail in the “Carburetors” handbook.
1 2
Adjusting carburetor
The procedure for adjusting the new C1Q-S45
392TI024 KN
carburetor has changed (see service notes 1.5.5).
11,8 mm 12,8 mm
0.46 in 0.50 in
On the new spacer flange (2), the cross section for
the flow of fuel-air mixture is larger than the previous
version (1).
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Technical Information 21.1999 Page 3
1.4 Shroud 1.5 Service notes
1.5.1 Original machine versions
If either the filter housing, carburetor or spacer
flange have to be replaced as separate parts, the
replacement parts must be the original versions.
L L The new shroud can be installed on both previous
LD
LA LA and new versions.
392TI025 KN
1.5.2 Earlier machine versions
Setting symbols In addition to the above notes (1.5.1), it is essential
Left: Original shroud to observe the service notes given in TI 41.97 under
Right: New shroud 1.3.
The new shroud has been modified in the area of
the carburetor adjusting screws so that it can be The previous carburetor 4137 120 0602 (LA screw,
used with either the original or new versions of the no control valve) used only on the production line
carburetors and machines. can be installed in place of the previous version
4137 120 0600 (H and LA screws, with control
valve). Carburetor 4137 120 0602 will be available
as a replacement from the factory in future and will
be supplied with full instructions. The instruction
sheet also indicates whether it is necessary to install
an ignition module with electronic cut-off.
Engine power can only be optimized or increased if
all the new parts are installed together with an
1 ignition module with electronic cut-off for
392TI026 KN
maximum engine speed.
Inside view of shroud
An improved shroud with insert has been available
some time. This insert helps improve the mounting
of the shroud and starter cover to the crankcase.
The new shroud is supplied as an assembly
together with the insert.
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)m~ge 4 Technical Information 21.1999
. Back off adjusting screw (1) on tensioner (2)
counterclockwise until the tensioner butts
against the spacer flange.
1
. Pull throttle trigger as far as stop and hold it
2 there (full throttle position).
1 . Check that throttle lever (3) butts against stop
on carburetor (see arrow)
. If necessary, turn adjusting screw (1) clockwise
366TI023 GM
until throttle lever touches the stop.
. Let go of throttle trigger and check setting.
Readjust if necessary.
! On earlier machine versions, install the
gaskets 4114 149 1205 (1) on both sides of the
heat shield (2). ! Control handle must be mounted on handlebar
of FS units with bike handle before making
1.5.3 New machine versions adjustments.
If the filter housing, carburetor or spacer flange have
to be replaced as separate parts, the replacement
parts must be the new versions.
A combination of new and original parts may result 1.5.5 Adjusting carburetor
in a loss of power and engine running problems.
1.5.4 Adjusting throttle cable
(C1Q-S45 carburetor)
LD
Adjust throttle cable as follows after installing the
392TI028 KN
new C1Q-S45 carburetor:
Preparations
2 On FC, FS:
Mount the cutting tool.
1
On FH, HL:
Check cutting blades and clean if
necessary (they must be clean, lubricated,
move freely and not be warped).
3
On HT:
Check chain tension.
392TI027 KN
. Check air filter and replace if necessary.
. Inspect spark arresting screen (if fitted) and
clean or replace as necessary.
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Technical Information 21.1999 Page 5
Standard setting 1.5.6 Outlet valve / Fixed jet
. Carefully screw the idle speed screw (LD) down
onto its seat counterclockwise (left-hand 1
thread), then open it 2 full turns clockwise from
that position.
2
Adjusting idle speed
. Carry out standard setting.
392TI029 KN
. Start the engine and warm it up.
Engine stops while idling:
. Turn the idle speed screw (LD) slowly clockwise The outlet valve (1) is installed in a precision
until the engine runs smoothly - process at the factory. This accuracy cannot be
the cutting tool must not rotate. achieved with normal service shop equipment.
STIHL’s recommendation: Do not replace outlet
valves!
Cutting tool rotates when engine is idling: The outlet valve helps ensure proper fuel delivery,
. urn the idle speed screw (LD) counter-clockwise providing the following points are observed:
until the cutting tool stops rotating - then turn . Replace pickup body periodically.
screw about 1 full turn in the same direction.
. Clean the fuel tank and storage can at regular
intervals.
Idling erratic, . Use the fuels and lubricants (gasoline, two-
poor acceleration: stroke engine oil) specified in the owner’s
. Turn the idle speed screw (LD) slowly counter- manual and shop manual.
clockwise, but not more than half a turn.
Use a standard screwdriver to unscrew the fixed jet
(2) for cleaning or replacement. Clean the jet in
fresh fuel and/or blow it clear with compressed air.
! Never attempt to clean the jet with needles,
wires or fibrous cloths.
Install the jet by screwing it down carefully and
tightening it by hand.
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)m~ge 6 Technical Information 21.1999
1.5.7 Filter housing / Choke shutter
Only combinations of the original or new versions of
the parts may be installed together. Do not mix
original parts with the new versions.
1.6 Summary
12 10
11 9
392TI031 GM
New carburetor 4137 120 0603 (C1Q-S45)
Item Part Name Previous New Rem.
1 Filter housing; 4137 140 2800 4137 140 2801 1)
including item 2:
2 Choke shutter 4137 141 3800 4137 141 3801 1)
All other parts as before
3 Carburetor C1Q-S28; 4137 120 0600 --- 1) 2)
including items 6, 7, 13 to 20:
4 Carburetor C1Q-S41; 4137 120 0602 --- 3)
including items 6, 7, 13 to 18:
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Technical Information 21.1999 Page 7
Item Part Name Previous New Rem.
5 Carburetor C1Q-S45; --- 4137 120 0603
including items 6 to 12:
6 Throttle shutter 4227 121 3300 4137 121 3300 1)
7 End cover 1123 121 0800 4128 121 0800 1)
8 Idle speed screw --- 4137 122 6300
9 Outlet valve --- 4137 122 5100
10 Fixed jet --- 4137 121 5601
11 Sealing plate --- 4119 121 0700
12 Sealing plate --- 4129 121 0700
13 Sealing plate 4226 121 0700 --- 1)
14 Low speed screw 4137 122 6800 --- 1)
15 Idle speed screw 1123 122 6200 --- 1)
16 Valve jet 4137 121 5401 --- 1)
17 Spring 1120 122 3005 --- 1)
18 Ball 1125 122 4200 --- 1)
19 Control valve 4137 120 8700 --- 1)
20 Washer 4226 121 8600 --- 1)
All other parts as carb C1Q-S28
21 Spacer flange 4137 121 1600 4137 121 1601 1)
22 Shroud; 4137 080 1600 4137 080 1601 4)
consisting of item 23:
23 Insert --- -*- 5)
Modification to be introduced from serial number 1 42 812 154
Remarks
1) Original version of part remains available as spare
2) Carburetor with control valve remains available for earlier version of machines (see TI 41.97).
3) Carburetor without control valve remains available for earlier version of machines
4) Original version of part is no longer available from factory
5) Part is not available as separate item
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)m~ge 8 Technical Information 21.1999
Last Technical Information on STIHL FH 75: 47.98
STIHL HL 75, 75 K: 44.98
STIHL HT 70: 35.98
STIHL HT 75: 14.1999
STIHL FC 75: 41.97
STIHL FS 75, 80, 85: 41.97
© 1999 Andreas STIHL AG & Co. Technical Documentation
Waiblingen D1/MTK-na 6565
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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.