Stihl Sr 420 User manual

SR 420
Instruction Manual2 - 25

Contents
1 Guide to Using this Manual.........................2
2 Safety Precautions and Working Techni‐
ques............................................................ 2
3 Assembling the Unit.................................... 8
4 Harness.......................................................9
5 Fuel........................................................... 10
6 Fueling...................................................... 11
7 Information Before You Start.................... 12
8 Starting / Stopping the Engine.................. 12
9 Calculating Required Quantity of Solution
.................................................................. 14
10 Metering Unit.............................................15
11 Filling the Container.................................. 16
12 Mistblowing............................................... 17
13 Cleaning the Air Filter............................... 17
14 Adjusting the Carburetor........................... 18
15 Spark Arresting Screen in Muffler............. 19
16 Spark Plug................................................ 20
17 Storing the Machine.................................. 20
18 Maintenance and Care..............................21
19 Minimize Wear and Avoid Damage...........22
20 Parts Subject to Wear and Tear................22
21 Main Parts.................................................23
22 Specifications............................................23
23 Maintenance and Repairs......................... 24
24 Disposal.................................................... 24
25 EC Declaration of Conformity................... 24
Dear Customer,
Thank you for choosing a quality engineered
STIHL product.
It has been built using modern production techni‐
ques and comprehensive quality assurance.
Every effort has been made to ensure your satis‐
faction and trouble-free use of the product.
Please contact your dealer or our sales company
if you have any queries concerning this product.
Your
Dr. Nikolas Stihl
1 Guide to Using this Manual
1.1 Pictograms
All the pictograms attached to the machine are
shown and explained in this manual.
1.2 Symbols in text
WARNING
Warning where there is a risk of an accident or
personal injury or serious damage to property.
NOTICE
Caution where there is a risk of damaging the
machine or its individual components.
1.3 Engineering improvements
STIHL's philosophy is to continually improve all
of its products. For this reason we may modify
the design, engineering and appearance of our
products periodically.
Therefore, some changes, modifications and
improvements may not be covered in this man‐
ual.
2 Safety Precautions and
Working Techniques
Special safety precautions must be
observed when working with the
power tool.
It is important that you read and
understand the User Manual before
commissioning and keep it in a safe
place for future reference. Non-com‐
pliance with the User Manual may
cause serious or even fatal injury.
Observe all applicable local safety regulations,
e.g. by trade organizations, social insurance
institutions, labor safety authorities etc.
If you have not used this machine before: Have
your dealer or other experienced user show you
how to handle your machine safely or attend a
specialist course.
Minors must never work with the machine –
except for young people over the age of 16 who
are being trained under supervision.
Children, animals and onlookers must not be
allowed near the machine.
When the machine is not in use, put it in a place
where it does not endanger others. Secure the
machine against unauthorized access.
The user is responsible for accidents or risks
involving third parties or their property.
English
2 0458-372-0121-C
© ANDREAS STIHL AG & Co. KG 2022
0458-372-0121-C. VA0.M21.
Printed on chlorine-free paper Printing inks contain vegetable oils, paper can be recycled.
Original Instruction Manual 0000000028_015_GB

Do not pass on or lend the machine to persons
who are not familiar with this model and its han‐
dling – always include the User Manual.
The use of machines that emit noise may be limi‐
ted to certain hours of the day as specified by
national and/or regional or local regulations.
Do not operate your machine if any of its compo‐
nents are damaged. Pay special attention to the
tightness of the container (no leaks).
Operate the power tool only if it is complete and
properly assembled.
Do not use a high-pressure washer to clean the
power tool. The solid jet of water may damage
parts of the unit.
2.1 Physical fitness
To operate the power tool you must be rested, in
good physical condition and mental health. If you
have any condition which may be aggravated by
strenuous work, check with your doctor before
operating a power tool.
If you have a pacemaker: The ignition system of
your machine produces an electromagnetic field
of very low intensity. This field may interfere with
some pacemakers. To reduce health risks,
STIHL recommends that persons with pacemak‐
ers consult their physician and the pacemaker
manufacturer before operating this tool.
Do not operate the power tool if you are under
the influence of any substance (drugs, alcohol)
which might impair vision, dexterity or judgment.
2.2 Applications
This mistblower is suitable for applying fungi‐
cides, herbicides and pesticides at ground level.
Spraying overhead is possible with mistblowers
equipped with a pressure pump. Typical areas of
application are in fruit, vegetable, wine and crop
growing, plantations, flower growing, grassland
and forestry.
Only use plant protection products that are spe‐
cifically approved for use in sprayers/mistblow‐
ers.
Do not use your power tool for any other purpose
because of the increased risk of accidents and
damage to the power tool. The product must not
be modified in any way - this may also lead to
accidents or damage to the unit.
2.3 Accessories and replacement
parts
Only use parts and accessories that are explicitly
approved for this power tool by STIHL or are
technically identical. If you have any questions in
this respect, consult your dealer. Use only high
quality parts and accessories. Otherwise there is
a risk of accidents and damage to the unit.
STIHL recommends the use of original STIHL
parts and accessories. They are specifically
designed to match the product and meet your
performance requirements.
Never attempt to modify your power tool in any
way since this may increase the risk of personal
injury. STIHL excludes all liability for personal
injury and damage to property caused while
using unauthorized attachments.
2.4 Clothing and equipment
Wear proper protective clothing and equipment
when using, filling and cleaning the power tool.
Follow the chemical manufacturer's user manual
with respect to protective equipment.
Immediately change work clothes contaminated
with plant control chemicals.
Clothing must be snug-fitting but
allow complete freedom of move‐
ment.
For some plant control chemicals it is
necessary to wear impermeable cov‐
eralls.
If you are spraying overhead, wear impermeable
head covering.
Avoid any clothing, scarves, neckties,
jewelry or anything that could get into
the air intake. Tie up and confine long
hair above your shoulders so that it
cannot be pulled into the machine.
Wear impermeable safety boots with
a non-slip sole which are resistant to
plant protection products.
Do not wear sandals or go barefoot.
WARNING
To reduce the risk of eye injuries,
wear close-fitting safety glasses in
accordance with European Standard
EN 166. Make sure the safety
glasses are a snug fit.
Wear a suitable respirator.
2 Safety Precautions and Working Techniques English
0458-372-0121-C 3

Wear "personal" sound protection, e.g. ear
defenders.
Breathing plant control chemicals may endanger
your health. Always wear a suitable respirator to
protect yourself against health risks and allergic
reactions. Observe warnings in the user manual
of the plant protection product and all applicable
local safety regulations, standards and ordinan‐
ces.
Wear impermeable gloves resistant to
plant control chemicals.
2.5 Handling Plant Control Chemi‐
cals
Read the user manual supplied with the plant
protection chemical prior to use. Follow the
instructions with respect to mixing, using, per‐
sonal protective equipment, storage and dis‐
posal.
Observe the legal requirements for handling
plant protection products.
Plant protection chemicals may contain substan‐
ces that are harmful to humans, animals, plants
and the environment – risk of poisoning and risk
of serious or fatal injuries!
Plant protection chemicals may be used only by
persons trained in their handling and the appro‐
priate first-aid measures.
Keep the user manual or label of the plant con‐
trol chemical available at all times in order to
inform the doctor about the chemical concerned
in an emergency. In an emergency, follow the
chemical manufacturer's instructions provided or
on the label.
2.5.1 Mixing the Spray Solution
Mix the plant protection product strictly in accord‐
ance with the manufacturer's instructions – incor‐
rect mixtures may produce toxic fumes or explo‐
sive solutions.
–Never spray liquid plant control chemicals
undiluted
–Prepare solution and fill the container outdoors
only or in well-ventilated locations.
–Only prepare sufficient solution for the job on
hand so that nothing is left over
–Mix different chemicals only in accordance
with the manufacturer's instructions – incorrect
mixtures may produce toxic fumes or explo‐
sive solutions
–Do not mix different plant protection products
unless such a mixture is approved by the man‐
ufacturer
2.5.2 Filling the Solution Container
–Stand the power tool securely on a level sur‐
face – do not fill the container above the maxi‐
mum mark
–To reduce the risk of injury, do not fill the
power tool while wearing it on your back.
–Close the valve lever before filling.
–When filling from central water supply, do not
immerse the end of the hose in the solution –
sudden low pressure in the system may cause
the solution to be sucked back into the water
supply
–Before filling the container with spray solution,
carry out test run with fresh water and check
all parts of the sprayer for leaks
–After filling, fit the filler cap and tighten it down
firmly
2.5.3 UseUse
–Work only in the open or in very well ventilated
locations, e.g. open greenhouses
–Do not eat, drink or smoke while working with
plant protection chemicals
–Never blow through nozzles or other compo‐
nents by mouth
–Avoid contact with plant control chemicals –
immediately change clothing contaminated
with plant control chemical
–Do not spray in windy conditions
Unfavorable weather conditions may result in an
incorrect concentration of the plant protection
product. Overdosing may damage plants and the
environment. Under-dosing may result in unsuc‐
cessful plant treatment.
In order to reduce the risk of damage to the envi‐
ronment and plants, do not operate the sprayer:
–in windy conditions
–at temperatures above 25°C in the shade
–in direct sunlight
In order to reduce the risk of accidents and dam‐
age to the power tool, never operate the power
tool with:
–flammable liquids
–viscous or sticky liquids
–caustic or corrosive chemicals
–liquids hotter than 50 °C
2.5.4 Bearing
–During work breaks, do not leave the power
tool in the hot sun or near any heat source
–Do not store spray solution in the container for
longer than one day
English 2 Safety Precautions and Working Techniques
4 0458-372-0121-C

–Store and transport spray solution only in
approved containers
–Never store the spray solution in containers
intended for foods, drinks or animal feed
–Do not store spray solution with foods, drinks
or animal feed
–Keep spray solution out of the reach of chil‐
dren and animals
–Store the power tool empty and clean
–Store the spray solution and power tool in a
place secured against unauthorized use.
–Store the spray solution and power tool in a
dry place protected from frost.
2.5.5 Disposal
Never dispose of residual chemicals or contami‐
nated rinsing solutions in waterways, drains,
sewers, street gutters or manholes.
–Dispose of residual chemicals and used con‐
tainers in accordance with local waste dis‐
posal regulations
2.6 Transporting the machine
Always stop the engine.
Transporting in a vehicle:
–Secure the machine against overturning, dam‐
age and fuel spillage
–The container must be empty and clean
2.7 Refueling
Gasoline is extremely flammable –
keep it away from naked flames – do
not spill any fuel – no smoking.
Always shut off the engine before refueling.
Do not fuel a hot engine – fuel may spill and
cause a fire.
Open the fuel cap carefully to allow any pressure
build-up in the tank to release slowly and to pre‐
vent fuel spraying out.
Only refuel the machine in a well ventilated
place. If you spill fuel, wipe the machine immedi‐
ately – if fuel gets on your clothing, change
immediately.
Check for fuel leakage! Never start
the engine if fuel has been spilled or
is leaking – Fatal burns may result!
After fueling, tighten down the screw-
type fuel cap as securely as possible.
This helps reduce the risk of unit vibrations caus‐
ing an incorrectly tightened fuel cap to loosen or
come off and spill quantities of fuel.
2.8 Before starting
Check that your power tool is properly assem‐
bled and in good condition, especially if it has
been subjected to unusually high loads for which
it was not designed (e.g. heavy impact or a fall).
–Check the fuel system for leaks, especially the
visible parts, e. g., fuel cap, hose connections,
manual fuel pump (only in machines with a
manual fuel pump). In case of leakage and
damage, do not start the engine – risk of fire!
Have the machine serviced by a dealer before
using it
–The setting lever must move easily to STOP or
0
–Throttle trigger must move freely and spring
back by itself to the idle position
–Check that the spark plug boot is secure – a
loose boot may cause sparking that could
ignite combustible fumes and cause a fire!
–Check the fuel system for leaks
–Check the condition and tightness of con‐
tainer, hose and metering unit
–Check condition of harness straps and replace
damaged or worn straps
To reduce the risk of accidents and personal
injury, do not operate your power tool if it is not
properly assembled and in good condition!
For emergencies: Practice removing and putting
down the power tool. To avoid damage, do not
throw the machine to the ground when practic‐
ing.
2.9 Starting the engine
Start the engine at least 3 meters from the fuel‐
ing spot, outdoors only.
Your power tool is designed to be operated by
one person only. Do not allow other persons in
the work area – even when starting.
Always proceed as described in the user manual.
Place the machine on level ground only, ensure
that you have a secure footing and hold the
machine securely.
If an assistant is required to put the power tool
on your back, make sure that
–the engine is running at idle speed
–the assistant is not standing in the area of the
exhaust outlet and breathing exhaust fumes
–the valve lever is closed
2 Safety Precautions and Working Techniques English
0458-372-0121-C 5

–the assistant is not standing in the area of the
outlet nozzle
–The assistant leaves the work area immedi‐
ately after you have put the power tool on your
back
2.10 Dusting and Granulate Spread‐
ing Attachment (Special Acces‐
sory)
Powder or dry granulate can be applied in the
dusting and spreading mode.
Observe legal requirements for handling the
chemicals.
Observe the User Manual or the label of the
plant protection product.
Use
Electrostatic charging with sparking can occur
when working with the dusting and spreading
attachment.
The risk is greatest
–in extremely dry weather conditions
–When using powdered products, which create
a highly concentrated dust cloud
To reduce the risk of accidents and damage to
the power tool, never operate it with explosive or
combustible materials
Do not apply sulphur or compounds containing
sulphur since they are highly explosive and have
a very low ignition point.
To reduce the risk of sparking, explosion or fire,
make sure the discharge system is completely
and properly mounted to the machine. It consists
of a conductive wire in the spray tube connected
to a metal chain. The metal chain must make
contact with a conductive surface to dissipate
electrostatic charges.
Do not operate your machine on a non-conduc‐
tive surface (e.g. plastic, asphalt).
Never operate your machine with a missing or
damaged discharge system.
Follow the mounting instructions supplied with
the "Dusting and Granulate Spreading Attach‐
ment".
2.11 Holding and guiding the
machine
372BA019 KN
Carry the power tool on your back with both har‐
ness straps – do not hang it over one shoulder.
Hold and control the blower tube with your right
hand on the control handle – even if you are left-
handed.
Work only slowly, moving in a forwards direction
– always observe the discharge area of the
blower tube – do not move backwards – risk of
tripping!
Keep the power tool and container upright. To
avoid the risk of chemical leaking from the con‐
tainer and causing injury,do not bend forwards.
2.12 While working
Do not direct the air blast towards bystanders
since the air flow can blow small objects at great
speed.
In the event of impending danger or in an emer‐
gency, switch off the engine immediately by mov‐
ing the setting lever to STOP or 0.
Quickly releasing power tool in an emergency:
–Open the fastener on the hip belt (special
accessory)
–Slip the straps off your shoulders
–Drop the power tool to the ground
Never leave a running machine unattended.
Take special care in slippery conditions – damp‐
ness, snow, ice, on slopes or uneven ground.
English 2 Safety Precautions and Working Techniques
6 0458-372-0121-C

Watch out for obstacles: Be careful of refuse,
tree stumps, roots and ditches which could
cause you to trip or stumble
Be particularly alert and cautious when wearing
hearing protection because your ability to hear
warnings (shouts, alarms, etc.) is restricted.
Take breaks when you start getting tired or feel‐
ing fatigue – risk of accidents!
Work calmly and carefully – in daylight conditions
and only when visibility is good. Proceed with
caution, do not put others in danger.
Do not work on a ladder or in unstable locations.
When working in open ground and gardens take
special care to avoid harming small animals.
To reduce the risk of electrocution, never operate
this power tool in the vicinity of live wires or
power cables.
Always clean the spray container and hose sys‐
tem before changing to a different plant protec‐
tion product.
As soon as the engine is running, the
power machine generates toxic
exhaust gas.As soon as the engine is
running, the power machine gener‐
ates toxic exhaust gas. These gases
may be odorless and invisible and
may contain unburned hydrocarbons
and benzene. Never work with the
machine in closed or poorly ventilated
rooms.
To reduce the risk of serious or fatal injury from
breathing toxic fumes, ensure proper ventilation
when working in trenches, hollows or other con‐
fined locations.
Stop work immediately if you start suffering from
nausea, headaches, impaired vision (e.g. your
field of vision gets smaller), impaired hearing,
dizziness, or impaired concentration – these
symptoms may possibly be the result of too-high
exhaust gas concentration – Risk of accidents!
Operate your power tool so that it produces a
minimum of noise and emissions – do not run the
engine unnecessarily, accelerate the engine only
when working.
To reduce the risk of fire, do not smoke while
operating or standing near your power tool. Com‐
bustible fuel vapor may escape from the fuel sys‐
tem.
If your power tool is subjected to unusually high
loads for which it was not designed (e.g. heavy
impact or a fall), always check that it is in good
condition before continuing work – see also
"Before Starting". Check the fuel system for
leaks and make sure the safety devices are
working properly. Do not continue operating your
power tool if it is damaged. In case of doubt, con‐
tact a dealer.
2.13 After finishing work
Close the valve lever.
Always shut off the engine before taking the
power tool off your back.
After finishing work, put the power tool down on
a level, non-flammable surface. Do not place the
machine near easily flammable materials (e.g.
wood chips, bark, dry grass, fuel) – risk of fire!
Check all parts of the power tool for leaks.
After finishing work, thoroughly clean the power
tool and wash your hands, face and, if neces‐
sary, your clothes.
Keep other people and animals away from the
areas that have been sprayed and do not walk
on them until the plant protection chemical has
dried.
2.14 Vibrations
Prolonged use of the power tool may result in
vibration-induced circulation problems in the
hands (whitefinger disease).
No general recommendation can be given for the
length of usage because it depends on several
factors.
The period of usage is prolonged by:
–Hand protection (wearing warm gloves)
–Work breaks
The period of usage is shortened by:
–Any personal tendency to suffer from poor cir‐
culation (symptoms: frequently cold fingers,
tingling sensations).
–Low outside temperatures.
–The force with which the handles are held (a
tight grip restricts circulation).
Continual and regular users should monitor
closely the condition of their hands and fingers. If
any of the above symptoms appear (e.g. tingling
sensation in fingers), seek medical advice.
2.15 Maintenance and Repairs
Service the machine regularly. Do not attempt
any maintenance or repair work not described in
2 Safety Precautions and Working Techniques English
0458-372-0121-C 7

the instruction manual. Have all other work per‐
formed by a servicing dealer.
STIHL recommends that you have servicing and
repair work carried out exclusively by an author‐
ized STIHL servicing dealer. STIHL dealers are
regularly given the opportunity to attend training
courses and are supplied with the necessary
technical information.
Only use high-quality replacement parts in order
to avoid the risk of accidents and damage to the
machine. If you have any questions in this
respect, consult a servicing dealer.
STIHL recommends the use of genuine STIHL
replacement parts. They are specifically
designed to match your model and meet your
performance requirements.
To reduce the risk of injury, always shut off the
engine before carrying out any maintenance or
repairs or cleaning the machine. – Exception:
Carburetor and idle speed adjustments.
Do not turn the engine over on the starter with
the spark plug boot or spark plug removed
unless the slide control / stop switch is on STOP
or 0 since there is otherwise a risk of fire from
uncontained sparking.
To reduce the risk of fire, do not service or store
your machine near open flames.
Check the fuel filler cap for leaks at regular inter‐
vals.
Use only a spark plug of the type approved by
STIHL and make sure it is in good condition –
see "Specifications".
Inspect the ignition lead (insulation in good con‐
dition, secure connection).
Check the condition of the muffler.
To reduce the risk of fire and damage to hearing,
do not operate your machine if the muffler is
damaged or missing.
Do not touch a hot muffler since burn injury will
result.
Vibration behavior is influenced by the condition
of the AV elements – check the AV elements at
regular intervals.
3 Assembling the Unit
NOTICE
The throttle cable is already connected and must
not be kinked during assembly.
3.1 Mounting the Elbow
372BA023 KN
23
1
The combination wrench and carburetor screw‐
driver are stowed on the underside of the
machine.
► Line up the stops on the elbow and stub and
push the elbow (1) into the stub (2) as far as it
will go. Fit the nut (3) in the hexagon recess in
the stub
► Insert the screw in the nut from the other side
and tighten moderately – the elbow must still
turn.
3.2 Mounting the Extension Tube
1
372BA024 KN
2
► Rotate the pleated hose (1) as far as stop.
► Swing control handle (2) to horizontal position.
English 3 Assembling the Unit
8 0458-372-0121-C

1
372BA025 KN
3
4
► Push the extension tube (3) into the pleated
hose (1) as far as it will go.
► The metering unit (4) must point in the same
direction as the control handle.
5
372BA026 KN
► Tighten down the clamp screw (5) (see
“Adjusting the Control Handle”).
3.3 Fitting the Liquid Hose
1
372BA027 KN
2
► Secure liquid hose (1) from the container to
the pleated hose with the retainer (2).
43
372BA028 KN
14
► Use hose clips (4) to secure hose (1) and
hose (3) to the stubs on the stop cock.
► Close the stop cock (move lever to vertical
position).
► Fill up with water and check all hose connec‐
tions for leaks.
3.4 Adjusting the Control Handle
1
2
372BA029 KN
► Put the machine on your back.
► Loosen the clamp screw (1).
► Move the control handle (2) along the tube to
the most comfortable position.
► Tighten down the clamp screw (1).
4 Harness
4.1 Attaching the Harness
0811BA009 KN
► Attach strap hook to the backplate.
4.2 Adjusting the Harness
373BA003 KN
► Pull the ends of the straps downward to
tighten the harness.
4 Harness English
0458-372-0121-C 9

4.3 Loosening the Harness
373BA004 KN
► Lift the tabs of the sliding adjusters.
► Adjust the harness so that the backplate fits
snugly and securely against your back.
4.4 Throwing Off Machine
Before using the machine, make yourself familiar
with how to release and throw off the backpack.
In an emergency, quickly throw the machine off
your back as follows:
► Open the quick-release fastener on the waist
belt (special accessory).
► Open the strap hook on the backplate by
snapping it forwards (arrow).
► Throw the machine to the rear.
5 Fuel
The engine requires a mixture of gasoline and
engine oil.
WARNING
Avoid direct skin contact with fuel and breathing
in of gasoline fumes.
5.1 STIHL MotoMix
STIHL recommends using STIHL MotoMix. This
pre-blended fuel is free of benzene and lead, is
distinguished by a high octane rating, and
always provides the proper mixing ratio.
STIHL MotoMix uses STIHL HP Ultra two-stroke
engine oil for optimum engine life.
MotoMix is not available in all markets.
5.2 Mixing fuel
NOTICE
Unsuitable fuels or a mixing ratio that deviates
from the specification can lead to severe engine
damage. The engine, seals, fuel lines and fuel
tank may be damaged if low-quality gasoline or
engine oil is used.
5.2.1 Gasoline
Use only high-quality gasoline with an octane rat‐
ing of at least 90 ROC – leaded or unleaded.
Gasoline with an alcohol component exceeding
10% can cause impaired engine performance in
engines with manually adjustable carburetors
and thus should not be used in these engines.
Engines with M-Tronic deliver full engine per‐
formance using gasoline with an alcohol compo‐
nent of up to 27% (E27).
5.2.2 Engine oil
If you mix the fuel yourself, use only STIHL two-
stroke engine oil or another high-performance
engine oil classified as JASO FB, JASO FC,
JASO FD, ISO-L-EGB, ISO-L-EGC or ISO-L-
EGD.
STIHL specifies STIHL HP Ultra two-stroke
engine oil or an equivalent high-performance
engine oil in order to maintain emission limits
over the machine’s service life.
5.2.3 Mixing ratio
with STIHL two-stroke engine oil 1:50; 1:50 =
1 part oil + 50 parts gasoline
5.2.4 Examples
Quantity of gaso‐
line
STIHL two-stroke
engine oil 1:50
Liters Liters (ml)
1 0.02 (20)
5 0.10 (100)
10 0.20 (200)
15 0.30 (300)
20 0.40 (400)
25 0.50 (500)
► Pour oil into an approved safety fuel canister
first, then add gasoline and mix thoroughly
English 5 Fuel
10 0458-372-0121-C

5.3 Storing fuel mixture
Store in approved safety fuel canisters only in a
dry, cool and secure place protected against light
and sunlight.
Fuel mixture deteriorates with age – mix only as
much as needed for a few weeks. Do not store
fuel mixture for longer than 30 days. The fuel
mixture can become unusable more quickly if
exposed to light, sunlight or low or high tempera‐
tures.
STIHL MotoMix however can be stored for up to
5 years without any problems.
► Shake the canister containing the fuel mixture
thoroughly before refueling
WARNING
Pressure may have built up in the canister –
open it carefully.
► The fuel tank and the canister in which fuel
mixture is stored should be cleaned thoroughly
from time to time
Residual fuel and the liquid used for cleaning
must be disposed of in accordance with regula‐
tions and without harming the environment!
6 Fueling
6.1 Preparations
373BA006 KN
► Before fueling, clean the filler cap and the area
around it to ensure that no dirt falls into the
tank.
► Position the machine so that the filler cap is
facing up.
STIHL recommends you use the STIHL filler noz‐
zle for fuel (special accessory).
6.2 Filling up with fuel
Take care not to spill fuel while fueling and do
not overfill the tank.
► Open the filler cap.
► Fill up with fuel.
► Close the filler cap.
6 Fueling English
0458-372-0121-C 11

WARNING
After fueling, tighten down the filler cap as
securely as possible by hand.
7 Information Before You
Start
NOTICE
With the engine stopped and before starting,
check the air intake grille between the backplate
and powerhead for blockages and clean if nec‐
essary. A protective screen is available as a spe‐
cial accessory to keep the air intake clear.
373BA037 KN
► Move the setting lever to the idel position.
The throttle cable disconnects itself from the
throttle trigger if the engine is not shut off in the
idle position.
The throttle cable reconnects itself automatically
when the setting lever is moved to the idle posi‐
tion.
8 Starting / Stopping the
Engine
8.1 Starting the Engine
► Observe safety precautions.
373BA008 KN
1
373BA009 KN
2
►Slide the stop switch (1) to #
► Move setting lever (2) to center position –
starting throttle.
The setting lever enables you to select and hold
any throttle position between (lower stop) idle
and full throttle (upper stop).
Set the lever to the idle position before switching
off the engine.
8.1.1 Before Starting
► Close the stop cock (3) (set to upright posi‐
tion).
English 7 Information Before You Start
12 0458-372-0121-C

8.1.2 If the engine is cold
373BA010 KN
373BA011 KN
►Turn the choke knob to g.
If the engine is warm
►Turn the choke knob to e.
► Also use this setting if the engine has been
running but is still cold.
8.2 Cranking
373BA012 KN
► Place the unit securely on the ground and
make sure that bystanders are well clear of
the nozzle outlet.
► Make sure you have a firm footing: Hold the
unit with your left hand on the housing and put
one foot against the base plate to prevent it
slipping.
► Hold the starter grip with your right hand.
► Pull the starter grip slowly until you feel it
engage and then give it a brisk strong pull.
NOTICE
Do not pull out the starter rope all the way – it
might otherwise break.
► Do not let the starter grip snap back. Guide it
slowly back into the housing so that the starter
rope can rewind properly.
When engine begins to fire
373BA013 KN
If the engine is cold:
►Move the choke knob to e and continue
cranking until the engine runs.
If the engine is warm:
► continue cranking until the engine runs.
8 Starting / Stopping the Engine English
0458-372-0121-C 13

8.3 As Soon as Engine Runs
373BA014 KN
2
► Move setting lever (2) to lower stop – the
engine settles down to idle speed.
8.4 Stopping the Engine
1
373BA015 KN
►Move the stop switch (1) to $
8.5 Other Hints on Starting
8.5.1 At very low outside temperatures
► Warm up the engine.
As soon as the engine runs:
► Move setting lever to lower stop – the engine
settles down to idle speed.
► Open throttle slightly – warm up the engine for
a short period.
8.5.2 If engine does not start
If you did not turn the choke knob to e quickly
enough after the engine began to fire, the com‐
bustion chamber is flooded.
► Remove the spark plug – see "Spark Plug".
► Dry the spark plug.
► Open the throttle wide.
► Crank the engine several times with the starter
to clear the combustion chamber.
► Install the spark plug – see "Spark Plug".
►Slide the stop switch to # and set the choke
knob to e – even if the engine is cold.
► Now start the engine.
8.5.3 If fuel tank has been run completely
dry and then refueled
► Pull the starter rope several times to prime the
fuel system.
9 Calculating Required
Quantity of Solution
9.1 Determining surface area (m2)
In the case of ground crops, simply multiply the
length of the field by its width.
The surface area of high-growing plants is calcu‐
lated approximately by measuring the length of
the rows and the average height of the foliage.
The result is multiplied by the number of rows
and then by two if both sides have to be treated.
The surface area in hectares is obtained by
dividing the number of square meters by 10,000.
Example:
A field 120 meters long and 30 meters wide has
to be treated with a pesticide.
Area:
120 m x 30 m = 3,600 m2
3,600 / 10,000 = 0.36 ha
9.2 Determining quantity of active
ingredient
Refer to the instructions supplied with the active
ingredient to determine:
–Required quantity of active ingredient for 1
hectare (ha).
–Concentration of active ingredient (mix ratio).
Multiply the required quantity of active ingredient
for 1 hectare by the area determined in hectares.
The result is the quantity of active ingredient
required for the area to be treated.
Example:
According to the maker’s instructions, 0.4 liters of
active ingredient are required per hectare to
obtain a concentration of 0.1%.
Quantity of active ingredient:
0.4 (l/ha) x 0.36 (ha) = 0.144 l
9.3 Determining quantity of solution
The quantity of solution required is calculated as
follows:
TWx 100 = TB
English 9 Calculating Required Quantity of Solution
14 0458-372-0121-C

K
TW = Quantity of active ingredient in liters
K K = Concentration in %
TB = Required quantity of solution in liters
Example:
The calculated quantity of active ingredient is
0.144 liters. According to the maker’s instruc‐
tions, the concentration is 0.1%.
Quantity of solution:
0.144 l x 100 = 144 l
0.1 %
9.4 Determining walking speed
Carry out a trial run with the machine fueled and
the container filled with water. Operate the spray
tube (swing it back and forth) as for the real run
described below. Determine the distance walked
in one minute.
Also use the trial run to check the selected work‐
ing width. The best working width for low-growing
crops is 4–5 m. Mark the working width with
stakes.
Dividing the distance walked in meters by the
time in minutes gives you the walking speed in
meters per minute (m/min).
Example:
The distance covered in one minute is 10
meters.
Walking speed:
10 m = 10 m/min
1 min
9.5 Determining discharge rate
The setting of the metering unit is calculated as
follows:
Va(l) x vb(m/min) x b(m) = Vc(l/min)
A (m2)
Va = Quantity of solution
vb = Walking speed
Vc = Discharge rate
b = Working width
A = Area
Example:
The values determined above and a working
width of 4 meters require the following setting on
the metering unit:
144 l x 10 (m/min) x 4 m = 1.6 l/min
3600 m2
Hectares (ha) have to be converted into m2 (ha x
10,000 = m2).
To adjust the required discharge rate see "Meter‐
ing Unit".
10 Metering Unit
10.1 Stop cock
► The stop cock (1) is closed when the lever is
upright.
► The stop cock (1) is open when the lever is
parallel to the hose.
► Adjust the discharge rate with the metering
knob – not the stop cock.
10 Metering Unit English
0458-372-0121-C 15

10.2 Metering knob
2
4
1
6
5
4
3
2
372BA005 KN
3
► The discharge rate can be infinitely varied by
turning the metering knob (2) on the noz‐
zle (3).
Position 1 = minimum flow rate
Position 6 = maximum flow rate
The numbers on the metering knob must be lined
up with the lug (4) under the knob.
10.3 Discharge rate without pres‐
sure pump
Standard metering knob
Discharge rate in l/min
Blower tube angle
Knob set‐
ting
‑30° 0° +30°
1 0.384 0.290 0.257
2 1.062 0.908 0.782
3 1.947 1.614 1.336
4 2.848 2.402 1.903
5 3.471 2.993 2.413
6 3.844 3.251 2.526
ULV metering knob
Discharge rate in l/min
Blower tube angle
Knob set‐
ting
‑30° 0° +30°
0.5 0.054 0.041 0.043
0.65 0.087 0.077 0.064
0.8 0.138 0.117 0.098
10.4 Discharge rate with pressure
pump (special accessory)
Standard metering knob
Discharge rate in l/min
Blower tube angle
Knob set‐
ting
‑30° 0° +30°
1 0.654 0.651 0.636
1.6 1.666 1.747 1.700
2 2.928 2.896 2.864
ULV metering knob
Discharge rate in l/min
Blower tube angle
Knob set‐
ting
‑30° 0° +30°
0.5 0.142 0.132 0.128
0.65 0.216 0.212 0.203
0.8 0.352 0.403 0.377
10.5 Checking metering unit
► Place the machine on the ground.
► Remove the baffle screen and pressure pump.
► Fill the container with water up to 10 liter mark.
► Set the metering knob to position 6.
► Start the machine.
► Hold the blower tube horizontally, run the
engine at full throttle, spray the contents of the
container down to the 5 liter mark and note the
time taken.
The time required to spray 5 liters fluid should be
between 140 and 170 seconds.
In case of deviations:
► Check the metering unit for contamination and
clean it if necessary.
► Check engine setting and correct if necessary.
If there is no improvement, contact your dealer
for assistance.
11 Filling the Container
► Stand the sprayer on a level surface.
► Close the stop cock.
372BA029 KN
► Fill up with thoroughly mixed spray solution –
do not exceed 13 liter mark (arrow).
English 11 Filling the Container
16 0458-372-0121-C

372BA021 KN
1
► The gasket (1) in the cap must always be
lubricated with grease.
► Fit the cap and tighten it down firmly.
12 Mistblowing
► Stop cock must be fully open while mistblow‐
ing – do not vary the flow rate with the stop
cock.
Different baffle screens enable the shape of the
spray jet to be varied.
12.1 Conical Screen
372BA006 KN
Spray solution is finely atomized – short, broad
and dense spray mist.
12.2 Deflector Screen
372BA007 KN
Diverts spray jet at an angle – for under-leaf
treatment of low-growing crops.
12.3 Dual Deflector Screen
372BA008 KN
Splits the spray jet in two – allows two closely
planted rows to be treated in one pass.
13 Cleaning the Air Filter
13.1 If there is a noticeable loss of
engine power
1
373BA017 KN
2
1
►Turn the choke knob to g.
► Take out the screw (1) and remove the filter
cover (2).
12 Mistblowing English
0458-372-0121-C 17

373BA018 KN
3
45
► Remove the main filter (3) from the cover and
inspect it – if it is dirty or damaged, fit a new
one.
Always install a new prefilter together with the
new main filter.
► Take the prefilter (4) out of the filter cover.
► If prefilter is wet, dry it – then knock it out on
the palm of your hand or blow it out with com‐
pressed air.
Always replace a damaged prefilter.
► Clean loose dirt from the filter cover and filter
chamber.
► Install the main filter (3) and prefilter (4) in the
filter cover.
► Fit the cover on the filter base (5) and tighten it
down firmly.
14 Adjusting the Carburetor
The carburetor comes from the factory with a
standard setting.
This setting provides an optimum fuel-air mixture
under most operating conditions.
With this carburetor it is only possible to adjust
the high speed and low speed screws within fine
limits.
14.1 Standard Setting
► Shut off the engine.
► Check the air filter and clean or replace if nec‐
essary.
► Check the spark arresting screen (not in all
models, country-specific) in the muffler and
clean or replace if necessary.
HL
373BA043 KN
► Carefully turn both adjusting screws counter‐
clockwise as far as stop.
► The high speed screw (H) is 1/4 turn open.
► The low speed screw (L) is 1/4 turn open.
14.2 Adjusting Idle Speed
► Carry out the standard setting.
► Start and warm up the engine.
LA
L
373BA044 KN
14.2.1 Engine stops while idling
► Turn the idle speed screw (LA) slowly clock‐
wise until the engine runs smoothly.
14.2.2 Erratic idling behavior, engine stops
even though setting of LA screw has
been corrected, poor acceleration
Idle setting is too lean
► Turn the low speed screw (L) counterclock‐
wise, no further than stop, until the engine
runs and accelerates smoothly.
14.2.3 Erratic idling behavior
Idle setting is too rich
► Turn the low speed screw (L) clockwise, no
further than stop, until the engine runs and
accelerates smoothly.
It is usually necessary to change the setting of
the idle speed screw (LA) after every correction
to the low speed screw (L).
English 14 Adjusting the Carburetor
18 0458-372-0121-C

14.3 Fine Tuning for Operation at
High Altitude
A slight correction of the setting may be neces‐
sary if engine does not run satisfactorily:
► Carry out the standard setting.
► Warm up the engine.
► Turn high speed screw (H) slightly clockwise
(leaner) – no further than stop.
NOTICE
After returning from high altitude, reset the car‐
buretor to the standard setting.
If the setting is too lean there is a risk of engine
damage due to insufficient lubrication and over‐
heating.
15 Spark Arresting Screen in
Muffler
WARNING
To reduce the risk of fire caused by hot particles
escaping from the machine, never operate the
machine without a spark arresting screen, or with
the spark arresting screen damaged. Do not
modify the muffler or spark arresting screen.
NOTICE
According to the law or regulations in some
countries or states, certain operations may only
be carried out if a properly serviced spark arrest‐
ing screen is provided.
373BA031 KN
12
If the engine power is decreasing or does not run
smoothly at maximum RPM, check the spark
arresting screen (not available in all versions) in
the muffler.
15 Spark Arresting Screen in Muffler English
0458-372-0121-C 19

WARNING
Wait for the engine to cool down completely
before performing this work.
► Use suitable tool to squeeze ends of clip (1)
together and then remove the clip.
► Pull the spark arresting screen (2) out of the
muffler.
► Clean the spark arresting screen if necessary.
► Replace the spark arresting screen if it is dam‐
aged or heavily carbonized.
16 Spark Plug
► If the engine is down on power, difficult to start
or runs poorly at idle speed, first check the
spark plug.
► Fit a new spark plug after about 100 operating
hours – or sooner if the electrodes are badly
eroded. Install only suppressed spark plugs of
the type approved by STIHL – see "Specifica‐
tions".
16.1 Removing the Spark Plug
► Move the stop switch to 0.
373BA016 KN
► Pull boot off the spark plug.
► Unscrew the spark plug.
16.2 Checking the Spark Plug
000BA039 KN
A
► Clean dirty spark plug.
► Check electrode gap (A) and readjust if neces‐
sary – see "Specifications".
► Rectify the problems which have caused foul‐
ing of the spark plug.
Possible causes are:
–Too much oil in fuel mix.
–Dirty air filter.
–Unfavorable running conditions.
1
000BA045 KN
WARNING
Arcing may occur if the adapter nut (1) is loose
or missing. Working in an easily combustible or
explosive atmosphere may cause a fire or an
explosion. This can result result in serious inju‐
ries or damage to property.
► Use resistor type spark plugs with a properly
tightened adapter nut.
16.3 Installing the spark plug
► Fit the spark plug by hand and screw it in
► Tighten spark plug with combination wrench
► Press the spark plug boot firmly onto the spark
plug
17 Storing the Machine
► Store the machine in a dry, frost-free and
secure location. Keep out of the reach of chil‐
dren and other unauthorized persons
English 16 Spark Plug
20 0458-372-0121-C