Technical Information · issue 16 of 1996
New blower BG 75
IssueTI 16/1996
Full text
Page 1 of 6
Technical Information
16.96
New STIHL BG 75 Blower - Type 4227
The BG 75 blower replaces the tried and tested • the familiar, conventional WT carburetor (Walbro
BG 72. The BG 75 has a more powerful engine. Its make) with two adjusting screws (H and L)
displacement of 25.4 cm3 (1.55 cu.in) gives the BG
75 more torque while its 0.75 kW (1.0 PS) rating and
means it is also more powerful than the predeces-
sor model.
• a fixed jet carburetor (Zama make) with no high
speed screw. This carburetor meets the strict
The BG 75 is designed for the same applications
US exhaust emission standards and appreciably
and users as the BG 72.
reduces CO and HC emissions.
The BG 75 is available in two different carburetor
versions:
)Technical Information 16.96 - Page 2
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1. Technical Description
2. Specifications
3. Special User Accessories
4. Service Accessories
5. Repairs
6. Spare Parts
1.====Technical Description
Main changes compared to the BG 72:
Crankshaft===================================================Air Filter
• Five-part; precision machined. • Improved filter material with longer service life
• Larger filter volume
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• Four-port technology (better mixture prepara- 0XIIOHU
tion, optimum combustion, lower emissions) • Two-chamber muffler
• Larger cooling area • Easier servicing of spark arresting screen
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• With two adjusting screws or one adjusting
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• ElastoStart starting handle for gentler starting
screw (see Carburetor specs.)
2.=======Specifications
2.1======Engine
2.1.1=Power Unit
Displacement: 25.4 cm3 (1.55 cu.in)
Bore: 34 mm (1.34 in)
Stroke: 28 mm (1.10 in)
Engine power: 0.75 kW (1.0 PS)
Max. permissible engine speed: (see Carburetor specs.)
Idling speed: (see Carburetor specs.)
Starter: ElastoStart system
Starter rope - diameter: 3.0 mm (0.12 in)
Starter rope - length: 800 mm (31.5 in)
Rewind spring - tension: 7 turns of rope rotor
Reserve pull: min. 1/2 turn
Muffler: Intake air silencer
Sound pressure level
Lpeq according to ISO 6081:1) Blower mode 89 dB(A)
Sound power level
Lweq according to ISO 3744:1) Blower mode 100 dB(A)
1)
Weighted equivalent level includes idling, full load and no load with the same duration of exposure
)Technical Information 16.96 - Page 3
2.1.2=Fuel System
Carburetor: all-position diaphragm carburetor with
integral fuel pump
B
A C
326TI002 KN
326TI003 KN
==================================================================Carburetor C 1Q S-30 =ZAMA
Carburetor WT 413 =WALBRO
A = valve jet B = idling fixed jet Ø 0.33 mm
C = valve jet with integral fixed jet
Ø 0.31 mm
Adjustments========================================WT 413 =Walbro make===================C 1Q S-30 =Zama make
Low speed screw1) L = open 1 full turn L = open 1 full turn
Idling speed 2,800 rpm 2,800 rpm
High speed screw1) H = open 1 full turn Not fitted
1)
Standard setting
2)
Maximum engine speed value not necessary for technical reasons,
because power is constantly taken off via the fanwheel
Fuel tank capacity: 0.5 l (0.9 US pt)
Fuel mixture: Regular branded gasoline and branded two-stroke engine oil
Octane number: 90 RON (U.S.A/Canada: min. 89 RON!)
Mixing proportions: 1:50 for STIHL two-stroke engine oil 1:50
*1:25 for other branded two-stroke engine oils
Air filter: Foam element (prefilter) and felt filter
Only two-stroke engine oils in a mixing proportion of 1:50 may be used in California!
)Technical Information 16.96 - Page 4
2.1.3=Ignition System
Gap: 0,2 ... 0,5 mm (0.008-0.019 in)
Ignition timing: 1.55 ... 2.25 mm (0.067-0.086 in) before TDC at n = 8,000 rpm
Ignition lead length: 160 mm (7.1 in)
Spark plug (suppressed): NGK BPMR 7 A
Heat range: 200
Electrode gap: 0,5 mm (0.02 in)
Spark plug thread: M 14 1.25, 9.5 mm (0.37 in) long
2.2=====Air Flow / Air Speed
Air flow
(blower mode): 640 m3/h (359 cfm)
Air speed
(blower mode): 60 m/s (198 ft/s)
2.3=====Weight
Complete unit
(w/out tools) 4.3 kg (9.6 lb)
3.======Special User Accessories
Vacuum attachment kit 4227 007 1000
Gutter cleaning kit 4227 007 1005
4.======Service Accessories
4.1=Special Tools
4.1.1=New Tools Required for the BG 75 series
Designation=======================Part No.=================Use=======================================Notes
Radial sealing ring
Extractor 5910 890 4400 Oil seals 1)
Spindle 5910 890 8400
1)
With extractor 0000 890 4400, the previous spindle can be replaced by spindle 5910 890 8400,
which is now 20 mm longer. The extractor is then identical with extractor 5910 890 4400.
4.1.2=Existing Special Tools
For all other repairs, the usual special tools
(same as BG 72) should be used.
)Technical Information 16.96 - Page 5
4.2====Aids
Carburetor parts kit 4133 007 1060 (WT 413)
Carburetor parts kit 4227 007 1060 (C 1Q S-30)
Gasket sheet 0457 281 4203
5.=====Repairs
If the unit is started up during repair or maintenan-
ce work, the safety regulations applicable in the
country of use and the safety instructions in the
Owner’s Manual must be followed.
5.1=Test Data
5.1.1=Leakage Testing
Power Unit
Crankcase leakage testing:
Subjected to pressure: overpressure = 0.5 bar
Subjected to a vacuum: underpressure = 0.5 bar
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Inlet needle testing: overpressure = 0.6 bar
5.1.2=Adjusting the Carburetor:
======Carburetor C 1Q S-30 =Zama
The carburetor does not have a high speed adju-
sting screw (H screw). Adjustment of the maximum
engine speed is not necessary.
The carburetor is set at the factory for optimum
fuel-air mixture.
Idling and part-load emissions are minimized by li-
miting the idle mixture (idling fixed jet).
Standard Setting
L = open 1=full turn
• Check air filter and clean if necessary
• Warm up the engine
L = `~refully screw the low speed screw (/) clock-
wise down on to its seat. Then open it one turn
counterclockwise (standard setting L = 1F.
Use LA =idle speed screw to set idling speed to
2,800 rpm.
If running problems occur even at standard set-
ting =e.g. engine stops while idling or accelera-
tion is poor=, the adjustments described on the
foolowing page should be carried out!
)Technical Information 16.96 - Page 6
Acceleration is poor or engine stops when id-===============Engine stops when turning, stops when swit-
ling for longer periods:====================================ching from full load to idling or is erratic when
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a) Carry out standard adjustment EL = 1F====================~F=`~rry out standard adjustment EL = 1F
b) Turn L =low speed screw 1/4 turn b) Turn L =low speed screw 1/8 turn clockwise
counterclockwise
c) Use LA =idle speed screw to set idling speed cF =rse LA =idle speed screw to set idling speed
to 2,800 rpm to 2,800 rpm
Repeat b) and c) if necessary! Repeat b) and c) if necessary!
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With carburetor WT 413, adjustment should be car-
ried out in the same way as with the WT 253.
5.1.3=Tightening Torques
Tightening
Fastener Thread Size For Part Torque (Nm)
Socket-head screw
Socket-head screw
IS-M 5x25
IS-M 5x25
Crankcase
Crankcase
fo 9.5
Spacer flange to cylinder 5.5
Socket-head screw IS-DG 5x24 Cylinder to crankcase 9.5
Socket-head screw IS-M 5x16 Muffler to cylinder 9.5
Socket-head screw IS-M 5x16 Starter to crankcase 5.5
Socket-head screw IS-M 5x16 Muffler to crankcase 9.5
Socket-head screw IS-M 4x25x10 Intake screen 2.5
M8 Carrier 20.0
Socket-head screw IS-M 4x20 Ignition module to cylinder 4.5
Plastoform screw IS-P 5.5x12 Rope rotor in starter cover 2.5
Plastoform screw IS-P 6x19 Shroud/fan housing 3.5
Plastoform screw IS-P 6x19 Fuel tank/fan housing 3.5
Nut M8 Shaft ZS/crankshaft 21.0
Nut M8 Fanwheel/shaft 18.0
Nut M5 Air filter cover and carburetor
to cylinder 4.0
Plastoform screw IS-P 6x26,5 Fan housing halves 5.5
Spark plug M 14x1.25 20.0
5.2=Repair Times
Repair times for the STIHL BG 75 are the same as
for the BG 72.
6.===Spare Parts
A separate parts list is available for the BG 75.
Andreas Stihl - D1/MTK-al
© 1996 Andreas Stihl Technical Documentation 5765 Page 2 of 6
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