STIHL BR 420
{
Instruction Manual
Manual de instrucciones
Warning!
Read and follow all safety
precautions in Instruction Manual –
improper use can cause serious or
fatal injury.
Advertencia!
Lea y siga todas las precauciones
de seguridad dadas en el manual
de instrucciones – el uso incorrecto
puede causar lesiones graves o
mortales.
Instruction Manual
1 - 34
Manual de
instrucciones
35 - 71
Contents
English
Guide to Using this Manual 2
Safety Precautions and Working
Techniques 2
Assembling the Unit 9
Fuel 12
Fueling 13
Information Before You Start 14
Starting / Stopping the Engine 14
Original Instruction ManualPrinted on chlorine-free paper
Operating Instructions 17
Cleaning the Air Filter 17
Engine Management 18
Adjusting the Carburetor 18
Catalytic Converter 19
Checking the Spark Plug 19
Spark Arresting Screen in Muffler 20
Replacing the Starter Rope and
Rewind Spring 21
Storing the Machine 23
Maintenance and Care 24
Main Parts 26
Specifications 27
Special Accessories 28
Printing inks contain vegetable oils, paper can be recycled.
Maintenance and Repairs 29
STIHL Incorporated Federal
Emission Control Warranty
Statement 29
STIHL Incorporated California
Exhaust and Evaporative
Emissions Control Warranty
Statement 31
Trademarks 33
Allow only persons who fully understand
this manual to operate your blower.
To receive maximum performance and
satisfaction from your STIHL blower, it is
important that you read, understand and
follow the safety precautions and the
operating and maintenance instructions
in chapter "Safety Precautions and
Working Techniques" before using your
blower. For further information you can
go to www.stihlusa.com.
Contact your STIHL dealer or the STIHL
distributor for your area if you do not
understand any of the instructions in this
manual.
Warning!
Because a blower is a high-speed tool,
some special safety precautions must
be observed as with any other power
tool to reduce the risk of personal injury.
Careless or improper use may cause
serious or even fatal injury.
{
© ANDREAS STIHL AG & Co. KG, 2011
0458-373-8621-B. M2.A11.GRA.
0000000023_001_GB
BR 420
1
English
Guide to Using this Manual
Pictograms
All the pictograms attached to or
embossed on the machine are shown
and explained in this manual.
Symbols in Text
Many operating and safety instructions
are supported by illustrations.
The individual steps or procedures
described in the manual may be marked
in different ways:
N A bullet marks a step or procedure.
A description of a step or procedure that
refers directly to an illustration may
contain item numbers that appear in the
illustration. Example:
N Loosen the screw (1).
N Lever (2) ...
In addition to the operating instructions,
this manual may contain paragraphs
that require your special attention. Such
paragraphs are marked with the
symbols and signal words described
below:
Danger!
Indicates an imminent risk of severe or
fatal injury.
Warning!
Indicates a hazardous situation which, if
not avoided, could result in severe or
fatal injury.
Caution!
Indicates a risk of property damage,
including damage to the machine or its
individual components.
Engineering Improvements
STIHL’s philosophy is to continually
improve all of its products. As a result,
engineering changes and improvements
are made from time to time. Therefore,
some changes, modifications and
improvements may not be covered in
this manual. If the operating
characteristics or the appearance of
your machine differ from those
described in this manual, please contact
your STIHL dealer for assistance.
Safety Precautions and
Working Techniques
Because a blower is
gasoline-powered and
produces a strong air
blast, special safety precautions must be
observed to reduce the
risk of personal injury.
It is important that you
read, fully understand
and observe the following
safety precautions and
warnings. Read the
instruction manual and
the safety precautions
periodically. Careless or
improper use may cause
serious or fatal injury.
Have your STIHL dealer show you how
to operate your power tool. Observe all
applicable local safety regulations,
standards and ordinances.
Warning!
Do not lend or rent your power tool without the instruction manual. Be sure that
anyone using it understands the information contained in this manual.
Warning!
The use of this machine may be
hazardous.
Use your blower only for clearing leaves,
grass, paper and dust in yards, gardens,
sport stadiums, parks, driveways and
parking lots.
2
BR 420
English
Warning!
Do not use it for other purposes, since
misuse may result in personal injury or
property damage, including damage to
the machine.
Warning!
Minors should never be allowed to use
this power tool. Bystanders, especially
children, and animals should not be
allowed in the area where it is in use.
Warning!
To reduce the risk of injury to bystanders and damage to property, never let
your power tool run unattended. When it
is not in use (e.g. during a work break),
shut it off and make sure that unauthorized persons do not use it.
Most of these safety precautions and
warnings apply to the use of all STIHL
blowers. Different models may have
different parts and controls. See the
appropriate section of your instruction
manual for a description of the controls
and the function of the parts of your
model.
Do not clean your machine with a
pressure washer. The solid jet of water
may damage parts of the machine.
Safe use of a blower involves
1. the operator
2. the power tool
3. the use of the power tool.
THE OPERATOR
Physical Condition
You must be in good physical condition
and mental health and not under the
influence of any substance (drugs,
alcohol, etc.) which might impair vision,
dexterity or judgment. Do not operate
this machine when you are fatigued.
Warning!
Be alert – if you get tired, take a break.
Tiredness may result in loss of control.
Working with any power tool can be
strenuous. If you have any condition
that might be aggravated by strenuous
work, check with your doctor before
operating this machine.
Warning!
Prolonged use of a power tool (or other
machines) exposing the operator to
vibrations may produce white finger disease (Raynaud's phenomenon) or
carpal tunnel syndrome.
These conditions reduce the hand's
ability to feel and regulate temperature,
produce numbness and burning
sensations and may cause nerve and
circulation damage and tissue necrosis.
All factors which contribute to white
finger disease are not known, but cold
weather, smoking and diseases or
physical conditions that affect blood
vessels and blood transport, as well as
high vibration levels and long periods of
exposure to vibration are mentioned as
factors in the development of white
finger disease. In order to reduce the
risk of white finger disease and carpal
tunnel syndrome, please note the
following:
– Most STIHL power tools are
available with an anti-vibration
("AV") system designed to reduce
the transmission of vibrations
created by the machine to the
operator's hands. An AV system is
recommended for those persons
using power tools on a regular or
sustained basis.
– Keep your hands warm.
– Keep the AV system well
maintained. A power tool with loose
components or with damaged or
worn AV elements will tend to have
higher vibration levels.
– Maintain a firm grip at all times, but
do not squeeze the handle with
constant, excessive pressure. Take
frequent breaks.
All the above-mentioned precautions do
not guarantee that you will not sustain
white finger disease or carpal tunnel
syndrome. Therefore, continual and
regular users should closely monitor the
condition of their hands and fingers. If
any of the above symptoms appear,
seek medical advice immediately.
Warning!
The ignition system of the STIHL unit
produces an electromagnetic field of a
very low intensity. This field may interfere with some pacemakers. To reduce
the risk of serious or fatal injury, persons
with a pacemaker should consult their
physician and the pacemaker manufacturer before operating this tool.
BR 420
3
English
Proper Clothing
Warning!
To reduce the risk of injury, the operator
should wear proper protective apparel.
Warning!
To reduce the risk of
injury to your eyes never
operate your power tool
unless wearing goggles
or properly fitted protec-
tive glasses with
adequate top and side protection complying with ANSI Z 87.1 (or your
applicable national standard).
Power tool noise may damage your
hearing. Wear sound barriers (ear plugs
or ear mufflers) to protect your hearing.
Continual and regular users should
have their hearing checked regularly.
Be particularly alert and cautious when
wearing hearing protection because
your ability to hear warnings (shouts,
alarms, etc.) is restricted.
Clothing must be sturdy
and snug-fitting, but allow
complete freedom of
movement.
Avoid loose-fitting jackets, scarfs, neckties,
jewelry, flared or cuffed
pants, unconfined long
hair or anything that
could become drawn into
the air intake. Secure hair
so it is above shoulder
level.
Good footing is very
important. Wear sturdy
boots with nonslip soles.
Steel-toed safety boots
are recommended.
Warning!
To reduce the risk of injury when the
inhalation of dust cannot be substantially controlled use an appropriate
respirator for the material being blown.
For more information see the "Working
conditions" section of these Safety
Precautions.
THE POWER TOOL
For illustrations and definitions of the
power tool parts see the chapter on
"Main Parts."
Warning!
Never modify this power tool in any way.
Only attachments supplied by STIHL or
expressly approved by STIHL for use
with the specific STIHL model are
authorized. Although certain unauthorized attachments are useable with
STIHL power tools, their use may, in
fact, be extremely dangerous.
If this 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. Check in particular that
the fuel system is tight (no leaks) and
that the controls and safety devices are
working properly. Do not continue
operating this machine if it is damaged.
In case of doubt, have it checked by your
STIHL servicing dealer.
Warning!
Small particles (e.g. dust) blown through
the blower tubes and nozzle can cause
a static charging of the blower tubes.
This is especially true in low humidity
and high dust conditions. In order to
reduce the risk of shock from static
charging and subsequent injury from
loss of control, your blower has features
designed to help reduce the build up of
static electricity in the blower tubes and
equalize the charge with the engine
and/or operator:
The control handle is designed to
conduct static electricity through the
throttle cable to the engine and from the
handle through the operator to the
ground.
STIHL offers an optional kit for use in
especially dry and dusty conditions. The
kit contains: (1) blower tubes made with
graphite to help conduct the charge back
to the control handle, and (2) a metal
ring with "wire" for insertion in the end
tube that helps reduce the build up of
static electricity.
If your blower is properly assembled and
you are still experiencing static shocks,
make sure that your footwear has
conductive soles and try operating your
unit without gloves, which may be
interfering with the conduction of the
charge.
4
BR 420
English
THE USE OF THE POWER TOOL
Transporting the Power Tool
Warning!
Always switch off the engine before taking the machine off your back and
putting it down. When transporting it in a
vehicle, properly secure it to prevent
turnover, fuel spillage and damage to
the unit.
Fuel
Your STIHL power tool uses an oilgasoline mixture for fuel (see the
chapter on "Fuel" of your instruction
manual).
Warning!
Gasoline is an extremely
flammable fuel. If spilled
and ignited by a spark or
other ignition source, it
can cause fire and seri-
ous burn injury or
property damage. Use extreme caution
when handling gasoline or fuel mix. Do
not smoke or bring any fire or flame near
the fuel or the power tool. Note that
combustible fuel vapor may escape
from the fuel system.
Fueling Instructions
Warning!
To reduce the risk of serious injury from
burns, never attempt to refuel the unit
until it has been completely removed
from the operator.
Warning!
Fuel your power tool in well-ventilated
areas, outdoors. Always shut off the
engine and allow it to cool before refueling. Gasoline vapor pressure may
build up inside the fuel tank depending
on the fuel used, the weather conditions
and the tank venting system.
In order to reduce the risk of burns and
other personal injury from escaping gas
vapor and fumes, remove the fuel filler
cap on your power tool carefully so as to
allow any pressure build-up in the tank
to release slowly. Never remove the fuel
filler cap while the engine is running.
Select bare ground for fueling and move
at least 10 feet (3 m) from the fueling
spot before starting the engine. Wipe off
any spilled fuel before starting your
machine.
Warning!
Check for fuel leakage
while refueling and during operation. If fuel
leakage is found, do not
start or run the engine
until the leak is fixed and
any spilled fuel has been wiped away.
Take care not to get fuel on your clothing. If this happens, change your
clothing immediately.
Unit vibrations can cause
an improperly tightened
fuel filler cap to loosen or
come off and spill quantities of fuel. In order to
reduce the risk of fuel
spillage and fire, tighten
the fuel filler cap by hand
as securely as possible.
Before Starting
Warning!
Always check your power tool for proper
condition and operation before starting,
particularly the throttle trigger, setting
lever and momentary stop switch. The
throttle trigger must move freely and
always spring back to the idle position.
Never attempt to modify the controls or
safety devices.
Warning!
Never operate your power tool if it is
damaged, improperly adjusted or maintained, or not completely or securely
assembled.
Warning!
Check that the spark plug boot is
securely mounted on the spark plug – a
loose boot may cause arcing that could
ignite combustible fumes and cause a
fire.
Keep the handles clean and dry at all
times; it is particularly important to keep
them free of moisture, pitch, oil, fuel mix,
grease or resin in order for you to
maintain a firm grip and properly control
your power tool.
BR 420
5
English
0009BA001 KN
Warning!
To reduce the risk of injury from parts
thrown by the fan wheel, check the fan
housing for damage (cracks or holes
that could allow foreign objects to contact the fan wheel). If any such damage
is found, stop using the unit and contact
your STIHL dealer for repair.
Warning!
Adjust carrying harness to suit your size
before starting work.
In an emergency, you may slip out of the
harness and throw off the machine
quickly. Try slipping out of the harness a
number of times before using the
machine in order to become
accustomed to it. Do not throw off the
machine while practicing as it could
damage the machine.
Starting
To reduce the risk of fire and burn
injuries, start the engine at least 10 feet
(3 m) from the fueling spot, outdoors
only.
Warning!
Your power tool is a one-person
machine. To reduce the risk of eye or
other injury from thrown objects, insure
that bystanders are at least 50 feet
(15 m) away during use. Stop operation
immediately if you are approached.
Warning!
This unit is equipped with an ignition
system that is normally in operational
readiness. After the setting lever is used
to stop the engine, it automatically
springs back to the "on" position. If the
engine is warm, it may be possible to
start it by simply pulling the starter rope,
with no further adjustments. To reduce
the risk of injury, be particularly alert to
keep children away from the unit.
For specific starting instructions, see the
appropriate section of your manual.
Place the power tool on firm ground or
other solid surface in an open area.
Maintain good balance and secure
footing.
Warning!
When you pull the starter grip, do not
wrap the starter rope around your hand.
Do not let the grip snap back, but guide
the starter rope to rewind it properly.
Failure to follow this procedure may
result in injury to your hand or fingers
and may damage the starter
mechanism.
Once the engine has started,
immediately blip the throttle trigger,
which should cause the choke knob to
move to the run position and allow the
engine to slow down to idle.
During Operation
Holding and Controlling the Power
Tool
The blower is designed for singlehanded operation with the right hand on
the control handle. It should be carried
as a backpack with the straps of the
harness over both shoulders.
Warning!
To reduce the risk of loss of control,
never carry the unit with the strap(s)
over one shoulder.
Wrap your fingers tightly around the
handle, keeping the control handle
cradled between your thumb and
forefinger. Keep your hand in this
position to have your machine under
control at all times.
Warning!
Special care must be taken in slippery
conditions (wet ground) and in difficult,
overgrown terrain. Watch for hidden
obstacles such as tree stumps, roots,
rocks, holes and ditches to avoid stumbling. For better footing, clear away
fallen branches, scrub and cuttings. Be
extremely cautious when working on
slopes or uneven ground.
6
BR 420
To reduce the risk of stumbling and loss
of control, do not walk backward while
operating the machine.
Warning!
To reduce the risk of injury from loss of
control, never work on a ladder or on
any other insecure support.
Working Conditions
Operate and start your power tool only
outdoors in a well-ventilated area.
Operate it under good visibility and
daylight conditions only. Work carefully.
Warning!
As soon as the engine is
running, this product generates toxic exhaust
fumes containing chemicals, such as unburned
hydrocarbons (including
benzene) and carbon monoxide, that
are known to cause respiratory problems, cancer, birth defects, or other
reproductive harm. Some of the gases
(e.g. carbon monoxide) may be colorless and odorless. To reduce the risk of
serious or fatal injury/illness from inhaling toxic fumes, never run the machine
indoors or in poorly ventilated locations.
If exhaust fumes become concentrated
due to insufficient ventilation, clear
obstructions from work area to permit
proper ventilation before proceeding
and/or take frequent breaks to allow
fumes to dissipate before they become
concentrated.
Warning!
Inhalation of certain dusts, especially
organic dusts such as mold or pollen,
can cause susceptible persons to have
an allergic or asthmatic reaction. Substantial or repeated inhalation of dust
and other airborne contaminants, in particular those with a smaller particle size,
may cause respiratory or other illnesses. This includes wood dust,
especially from hardwoods, but also
from some softwoods such as Western
Red Cedar. Control dust at the source
where possible. Use good work practices, such as operating the unit so that
the wind or operating process directs
any dust raised by the power tool away
from the operator. Follow the recommendations of EPA/OSHA/NIOSH and
occupational and trade associations
with respect to dust ("particulate matter"). When the inhalation of dust cannot
be substantially controlled, i.e., kept at
or near the ambient (background) level,
the operator and any bystanders should
wear a respirator approved by
NIOSH/MSHA for the type of dust
encountered.
Warning!
If the substance being blown is a commercial substance, review the material
safety data sheet for that substance and
/ or consult the material manufacturer /
supplier. The state of California and
some other authorities, for instance,
have published lists of substances
known to cause cancer, reproductive
toxicity, etc.
English
Warning!
Breathing asbestos dust is dangerous
and can cause severe or fatal illness,
respiratory illness or cancer. The use
and disposal of asbestos-containing
products have been strictly regulated by
OSHA and the Environmental Protection Agency. If you have any reason to
believe that you might be blowing or otherwise disturbing asbestos, immediately
contact your employer or a local OSHA
representative.
Warning!
Dust with silica in its composition may
contain crystalline silica. Silica is a basic
component of sand, quartz, brick, clay,
granite and numerous other minerals
and rocks, including masonry and concrete products. Repeated and / or
substantial inhalation of airborne crystalline silica can cause serious or fatal
respiratory disease, including silicosis.
In addition, the state of California and
some other authorities have listed
respirable crystalline silica as a substance known to cause cancer. When
encountering such materials, always
follow the respiratory precautions mentioned above.
Operating Instructions
Warning!
In the event of an emergency, switch off
the engine immediately – move the setting lever to 0 or STOP.
BR 420
7
English
Warning!
Even though bystanders should be kept
away from the running power tool, never
work alone. Keep within calling distance
of others in case help is needed.
Stop the engine immediately if you are
approached.
Warning!
To reduce the risk of personal injury, do
not direct air blast towards bystanders,
since the high pressure of the air flow
can injure eyes and can blow small
objects at great speed.
Warning!
The blower fan between the air intake
and output openings rotates whenever
the engine is running.
Never insert any foreign object into the
air intake of the machine or into the
nozzle of the blower. It will damage the
fan wheel and may cause serious injury
to the operator or bystanders as a result
of the object or broken parts being
thrown out at high speed.
Do not place the blower on the ground
when operating at high speed, because
small objects such as sand, grass, dust,
etc. may be pulled into the air intake and
damage the fan wheel. It is best to turn
the machine off when putting it on the
ground.
Warning!
The muffler and other parts of the
engine (e.g. fins of the cylinder, spark
plug) become hot during operation and
remain hot for a while after stopping the
engine. To reduce risk of burns do not
touch the muffler and other parts while
they are hot.
Warning!
To reduce the risk of fire and burn injury,
keep the area around the muffler clean.
Remove excess lubricant and all debris
such as pine needles, branches or
leaves. Let the engine cool down sitting
on concrete, metal, bare ground or solid
wood (e.g. the trunk of a felled tree)
away from any combustible substances.
Warning!
Never modify your muffler. The muffler
could be damaged and cause an
increase in heat radiation or sparks,
thereby increasing the risk of fire and
burn injury. You may also permanently
damage the engine. Have your muffler
serviced and repaired by your STIHL
servicing dealer only.
Using the Vacuum Attachment
(special accessory)
The vacuum is designed to pick up dry
material such as leaves, grass, small
twigs and bits of paper.
Warning!
To reduce the risk of personal injury from fire and
explosion, never attempt
to vacuum hot or burning
substances (e.g. smoldering ashes, glowing
cigarettes)
or combustible fluids (e.g.
gasoline, paint thinners).
MAINTENANCE, REPAIR AND
STORING
Maintenance, replacement, or repair
of the emission control devices and
systems may be performed by any
nonroad engine repair establishment
or individual. However, if you make a
warranty claim for a component
which has not been serviced or
maintained properly or if
nonapproved replacement parts were
used, STIHL may deny coverage.
Warning!
Use only identical STIHL replacement
parts for maintenance and repair. Use of
non-STIHL parts may cause serious or
fatal injury.
Strictly follow the maintenance and
repair instructions in the appropriate
section in this instruction manual.
Please refer to the maintenance chart in
this instruction manual.
8
BR 420
English
353BA002 KN
2
3
1
Warning!
Always stop the engine and make sure
that the fan is stopped before doing any
maintenance or repair work or cleaning
the power tool. Do not attempt any
maintenance or repair work not
described in this instruction manual.
Have such work performed by your
STIHL servicing dealer only.
Do not clean your machine with a
pressure washer. The solid jet of water
may damage parts of the machine. Tighten all nuts, bolts and screws except
Warning!
Use the specified spark plug and make
sure it and the ignition lead are always
clean and in good condition. Always
press spark plug boot snugly onto spark
plug terminal of the proper size. (Note: If
terminal has detachable SAE adapter
nut, it must be securely attached.) A
loose connection between spark plug
terminal and the ignition wire connector
in the boot may create arcing that could
ignite combustible fumes and cause a
fire.
Warning!
Never test the ignition system with the
boot removed from the spark plug or
with a removed spark plug, since uncontained sparking may cause a fire.
Warning!
Do not operate your power tool if the
muffler is damaged, missing or modified. An improperly maintained muffler
will increase the risk of fire and hearing
loss. If your muffler was equipped with a
spark-arresting screen to reduce the
risk of fire, never operate your power
tool if the screen is missing or damaged.
Remember that the risk of forest fires is
greater in hot or dry weather.
the carburetor adjustment screws after
each use.
For maintenance items please also refer
to the maintenance chart in this
instruction manual.
Store the power tool in a dry and high or
locked location out of reach of children.
Before storing for longer than a few
days, always empty the fuel tank. See
chapter "Storing the machine" in this
instruction manual.
Store fuel in an approved and properly
labeled safety-type canister only. Take
care when handling gasoline! For health
and safety reasons, avoid direct contact
with the skin and avoid inhaling fuel
vapor!
Assembling the Unit
Fitting the Elbow
A combination wrench and carburetor
screwdriver are stowed on the underside
of the machine.
The throttle cable is already
connected and must not be kinked
during assembly.
N Line up the stops on the elbow and
stub and push the elbow (1) into the
stub (2) as far as it will go.
N Fit the nut (3) in the hexagon recess
in the stub
N Insert the screw in the nut from the
other side and tighten moderately –
the elbow must still turn.
BR 420
9
English
373BA033 KN
7
4
8
10
6
11
5
9
a
b
Mounting Blower Tube with Straight
*
Nozzle
Operate the machine only with a
properly mounted blower tube
and nozzle.
N Secure the throttle cable (4) in
position with the retainer (5).
N Push the blower tube (6) into the
pleated hose (7).
N Push the nozzle (8) onto the blower
tube (1) as far as lug (9),
position (a) (long) or position (b)
(short), and rotate the nozzle in the
direction of the arrow to it lock in
position.
*
Depending on model
10
N Rotate the pleated hose (7)
counterclockwise as far as stop and
leave it in that position.
N Turn the control handle (10)
counterclockwise to the horizontal
position and tighten down the clamp
screw (11).
BR 420
Mounting Blower Tube with Curved
373BA039 KN
7
12
10
6
11
9
a
b
13
*
Nozzle
English
Operate the machine only with a
properly mounted blower tube
and nozzle.
N Push the blower tube (6) into the
pleated hose (7).
N Push the blower tube (12) onto the
blower tube (6) as far as lug (9),
position (a) (long) or position (b)
(short), and rotate the nozzle in the
direction of the arrow to it lock in
position.
N Fit the nozzle (13) on the end of the
blower tube (12) and turn it
clockwise to engage the bayonet
coupling.
*
Depending on model
BR 420
N Rotate the pleated hose (7)
counterclockwise as far as stop and
leave it in that position.
N Rotate the complete blower tube
assembly until the nozzle discharge
opening points in the same direction
as the control handle.
N Turn the control handle (10)
counterclockwise to the horizontal
position.
N Tighten down the clamp screw (11).
11
English
11
10
373BA002 KN
373BA003 KN
373BA004 KN
Adjusting the Control Handle
N Put the machine on your back.
N Loosen the clamp screw (11).
N Move the control handle (10) along
the tube to the most comfortable
position.
N Tighten down the clamp screw (11).
Adjusting the Harness Straps
N Pull the ends of the straps
downwards to tighten the harness.
Loosening the Harness Straps
N Lift the tabs of the sliding adjusters.
N Adjust the harness straps so that
the backplate fits snugly and
securely against your back.
Fuel
This engine is certified to operate on
unleaded gasoline and the STIHL twostroke engine oil at a mix ratio of 50:1.
Your engine requires a mixture of highquality gasoline and quality two-stroke
air cooled engine oil.
Use mid-grade unleaded gasoline with a
minimum octane rating of 89 (R+M/2). If
the octane rating of the mid-grade
gasoline in your area is lower, use
premium unleaded fuel.
Fuel with a lower octane rating may
increase engine temperatures. This, in
turn, increases the risk of piston seizure
and damage to the engine.
The chemical composition of the fuel is
also important. Some fuel additives not
only detrimentally affect elastomers
(carburetor diaphragms, oil seals, fuel
lines, etc.), but magnesium castings and
catalytic converters as well. This could
cause running problems or even
damage the engine. For this reason
STIHL recommends that you use only
high-quality unleaded gasoline!
Gasoline with an ethanol content of
more than 10% can cause running
problems and major damage in engines
with a manually adjustable carburetor
and should not be used in such engines.
Engines equipped with M-Tronic can be
run on gasoline with an ethanol content
of up to 25% (E25).
Use only STIHL two-stroke engine oil or
equivalent high-quality two-stroke
engine oils that are designed for use
only in air cooled two-cycle engines.
12
BR 420
English
373BA030 KN
We recommend STIHL HP Ultra 2-Cycle
Engine Oil since it is specially
formulated for use in STIHL engines.
Do not use BIA or TCW rated (twostroke water cooled) mix oils or other
mix oils that state they are for use in both
water cooled and air cooled engines
(e.g., outboard motors, snowmobiles,
chain saws, mopeds, etc.).
Take care when handling gasoline.
Avoid direct contact with the skin and
avoid inhaling fuel vapor. When filling at
the pump, first remove the canister from
your vehicle and place the canister on
the ground before filling. Do not fill fuel
canisters that are sitting in or on a
vehicle.
The canister should be kept tightly
closed in order to avoid any moisture
getting into the mixture.
The machine‘s fuel tank and the canister
in which fuel mix is stored should be
cleaned as necessary.
Fuel mix ages
Only mix sufficient fuel for a few days
work, not to exceed 3 months of storage.
Store in approved fuel-canisters only.
When mixing, pour oil into the canister
first, and then add gasoline. Close the
canister and shake it vigorously by hand
to ensure proper mixing of the oil with
the fuel.
Gasoline
Oil (STIHL 50:1 or equivalent high-quality oils)
US gal. US fl.oz
12.6
2 1/2 6.4
5 12.8
Dispose of empty mixing-oil canisters
only at authorized disposal locations.
Fueling
Before fueling, clean the filler cap and
the area around it to ensure that no dirt
falls into the tank.
Always thoroughly shake the mixture in
the canister before fueling your
machine.
Warning!
In order to reduce the risk of burns or
other personal injury from escaping gas
vapor and fumes, remove the fuel filler
cap carefully so as to allow any pressure build-up in the tank to release
slowly.
Warning!
After fueling, tighten fuel cap as
securely as possible by hand.
BR 420
13
English
373BA007 KN
373BA037 KN
373BA008 KN
1
373BA009 KN
2
Change the fuel pick up body every
year
Before storing your machine for a long
period, drain and clean the fuel tank and
run engine until carburetor is dry.
Information Before You
Start
With the engine stopped and
before starting, check the air
intake grille between the
backplate and powerhead for
blockages and clean if necessary.
A protective screen is available as
a special accessory to keep the
air intake clear.
Only models with catalytic converter
N Move the setting lever to the idle
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 position.
Starting / Stopping the
Engine
Starting the engine
N Observe safety precautions.
N Slide the stop switch (1) to #
N 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.
14
BR 420
English
373BA010 KN
373BA011 KN
373BA012 KN
373BA013 KN
If the engine is cold
N Turn the choke knob to g.
If the engine is warm
N Turn the choke knob to e.
N Also use this setting if the engine
has been running but is still cold.
Starting
N Place the unit securely on the
ground and make sure that
bystanders are well clear of the
nozzle outlet.
N 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.
N Hold the starter grip with your right
hand.
N Pull the starter grip slowly until you
feel it engage and then give it a brisk
strong pull.
Do not pull out the starter rope all
the way – it might otherwise
break.
N Do not let the starter grip snap back.
Guide it slowly back into the housing
so that the starter rope can rewind
properly.
When the engine begins to fire:
If the engine is cold:
N Move the choke knob to
e and
continue cranking until the engine
runs.
If the engine is warm:
N Continue cranking until the engine
runs.
BR 420
15
English
373BA014 KN
2
1
373BA015 KN
373BA016 KN
As soon as the engine runs
N Move setting lever (2) to lower stop
– the engine settles down to idle
speed.
To shut down the engine
N Slide the stop switch (1) to $ .
Other hints on starting
At very low outside temperatures
N Warm up the engine.
As soon as the engine runs:
N Move setting lever to lower stop –
the engine settles down to idle
speed.
N Open throttle slightly – warm up the
engine for a short period.
16
If the engine does not start
If you did not turn the choke knob to e
quickly enough after the engine began to
fire, the combustion chamber is flooded.
N Pull off the spark plug boot.
N Unscrew and dry off the spark plug.
N Move the stop switch to 0.
N Open the throttle wide.
N Crank the engine several times with
the starter to clear the combustion
chamber.
N Refit the spark plug and connect the
spark plug boot.
N Slide the stop switch to
# and set
the choke knob to e – even if the
engine is cold.
N Now start the engine.
If fuel tank has been run completely
dry and then refueled
N Pull the starter rope several times to
prime the fuel system.
BR 420
Operating Instructions Cleaning the Air Filter
1
373BA017 KN
2
1
373BA018 KN
3
4
5
English
During Operation
After a long period of full throttle
operation, allow the engine to run for a
short while at idle speed so that engine
heat can be dissipated by the flow of
cooling air. This protects enginemounted components (ignition,
carburetor) from thermal overload.
After Finishing Work
Storing for a short period: Wait for the
engine to cool down. Empty the fuel tank
and keep the machine in a dry place,
well away from sources of ignition, until
you need it again. For longer out-ofservice periods – see "Storing the
Machine".
If there is a noticeable loss of engine
power
N Turn the choke knob to g.
N Take out the screw (1) and remove
the filter cover (2).
N 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.
N Take the prefilter (4) out of the filter
cover.
N If prefilter is wet, dry it – then knock
it out on the palm of your hand or
blow it out with compressed air.
Always replace a damaged prefilter.
N Clean loose dirt from the filter cover
and filter chamber.
N Install the main filter (3) and
prefilter (4) in the filter cover.
N Fit the cover on the filter base (5)
and tighten it down firmly.
BR 420
17
English
H
L
373BA043 KN
LA
L
373BA044 KN
Engine Management Adjusting the Carburetor
Exhaust emissions are controlled by the
design of the fundamental engine
parameters and components (e.g.
carburation, ignition, timing and valve or
port timing) without the addition of any
major hardware.
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.
Standard Setting
N Stopping the engine
N Check the air filter and clean or
replace as necessary.
N Check the spark arresting screen
(not in all versions) in the muffler
and clean or replace as necessary.
N Carefully turn both adjusting screws
counterclockwise as far as stop.
N The high speed screw (H) is 1/4 turn
open.
N The low speed screw (L) is 1/4 turn
open.
N Start and warm up the engine.
Adjusting Idle Speed
Engine stops while idling
N Turn the idle speed screw (LA)
slowly clockwise until the engine
runs smoothly.
Erratic idling behavior, engine stops
even though setting of LA screw has
been corrected, poor acceleration
Idle setting is too lean:
N Turn the low speed screw (L)
counterclockwise, no further than
stop, until the engine runs and
accelerates smoothly.
Erratic idling behavior
Idle setting is too rich
N 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).
18
BR 420
English
000BA002 KN
Fine tuning for operation at high
altitude
A slight correction of the setting may be
necessary if the engine does not run
satisfactorily:
N Check the standard setting.
N Warm up the engine.
N Turn high speed screw (H)
clockwise (leaner) – no further than
stop.
If the setting is too lean there is a
risk of engine damage due to
insufficient lubrication and
overheating.
Catalytic Converter Checking the Spark Plug
Power tools with a catalytic converter
(depending on model) must be run on a
50 : 1 mixture of unleaded gasoline
and STIHL two-stroke engine oil or
equivalent two-stroke engine oil – see
chapter on "Fuel".
The catayltic converter integrated in the
muffler reduces the harmful emissions in
the exhaust gas.
The correct carburetor setting (if
adjustable) and strict observance of the
prescribed mix ratio of gasoline and twostroke engine oil are essential to
minimize harmful emissions and ensure
a long catalytic converter service life.
Wrong fuel mix (too much engine oil in
the gasoline), a dirty air filter and
unfavorable running conditions (mostly
at part throttle etc.) affect the condition
of the spark plug. These factors cause
deposits to form on the insulator nose
which may result in trouble in operation.
If engine is down on power, difficult to
start or runs poorly at idling speed, first
check the spark plug.
N Remove spark plug – see "Starting /
Stopping the Engine".
N Clean dirty spark plug.
N Check electrode gap (A) and
readjust if necessary – see
"Specifications".
N Use only resistor type spark plugs of
the approved range.
BR 420
19
English
000BA036 TR
1
373BA031 KN
1
2
Rectify problems which have caused
fouling of spark plug:
N Too much oil in fuel mix.
N Dirty air filter.
N Unfavorable running conditions,
e.g. operating at part load.
Fit a new spark plug after approx. 100
operating hours or earlier if the
electrodes are badly eroded.
Warning!
To reduce the risk of fire and burn injury,
use only spark plugs authorized by
STIHL. Always press spark plug boot (2)
snugly onto spark plug terminal (1) of
the proper size. (Note: If terminal has
detachable SAE adapter nut, it must be
attached.) A loose connection between
spark plug boot and ignition wire connector in the boot may create arcing that
could ignite combustible fumes and
cause a fire.
Spark Arresting Screen in
Muffler
If the engine is down on power or does
not run smoothly at maximum RPM,
check the spark arresting screen (not
fitted in all versions) in the muffler.
Wait for the engine to cool
down completely before
performing this work.
N Use suitable tool to squeeze ends of
clip (1) together and then lift the clip
away.
N Pull the spark arresting screen (2)
out of the muffler.
N Clean the spark arresting screen if
necessary.
N If the spark arresting screen is
damaged or heavily carbonized, fit a
new one.
20
BR 420
Replacing the Starter Rope
111
373BA025 KN
2
1
353BA034 KN
3
5
4
353BA041 KN
7
6
and Rewind Spring
English
Replacing the starter rope
N Take out the screws (1).
N Remove the starter cover (2) from
the housing.
BR 420
N Remove the spring clip (3).
N Remove the rope rotor with
washer (4) and pawl (5).
N Pry the cap (6) out of the grip.
N Remove the remaining rope from
the rotor and starter grip.
N Tie a simple overhand knot in the
new rope and then thread it through
the top of the grip and the rope
bushing (7).
N Refit the cap in the grip.
21
Loading...