Stihl BR 420 User manual

Instruction ManualSTIHL BR 420
BA_BR340_01_U_F3.book Seite 0 Dienstag, 24. Juni 2003 9:58 09
STIH)

1BR 420
English
BA_SE_003_002_01_13.fmPrinted on chlorine-free paper.
Printing inks contain vegetable oils; paper can be recycled.
© ANDREAS STIHL AG & Co. KG, 2008 0458 373 0121 B. M0,7. K8. Rei. Printed in Germany
STIHl
Contents
Guide to Using this Manual .............. 2
Safety Precautions and
Working Techniques ......................... 3
Assembling the Blower ..................... 9
Fuel ................................................ 11
Fueling ............................................ 12
Information Before You Start .......... 13
Starting / Stopping the Engine ........ 13
Operating Instructions .................... 16
Cleaning the Air Filter ..................... 16
Adjusting the Carburetor ................ 17
Catalytic Converter ......................... 19
Checking the Spark Plug ................ 19
Engine Running Behavior ............... 20
Spark Arresting Screen
in Muffler ......................................... 20
Replacing Starter Rope and
Rewind Spring ................................ 21
Storing the Machine ........................ 24
Maintenance Chart ......................... 25
Minimize Wear and
Avoid Damage ................................ 26
Parts and Controls .......................... 27
Specifications ................................. 28
Special Accessories ....................... 29
Maintenance and Repairs ............... 29
Certificate of Conformity ................. 30
Quality Certification ........................ 30
Dear Customer,
Thank you for choosing a quality
engineered STIHL product.
This machine has been built using
modern production techniques and
comprehensive quality assurance.
Every effort has been made to ensure
your satisfaction and troublefree use
of the machine.
Please contact your dealer or our
sales company if you have any
queries concerning your machine.
Hans Peter Stihl

2
English
BR 420
Pictograms
All the pictograms attached to the
machine are shown and explained in
this manual.
The operating and handling instructions
are supported by illustrations.
Symbols in text
The individual steps or procedures
described in the manual may be marked
in different ways:
:A bullet marks a step or procedure
without direct reference to an
illustration.
A description of a step or procedure that
refers directly to an illustration may
contain item numbers that appear in the
illustration.
Example:
Loosen the screw (1)
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 described below:
Warning where there is a risk of an
accident or personal injury or
serious damage to property.
Caution where there is a risk of
damaging the machine or its
individual components.
Note or hint which is not essential
for using the machine, but may
improve the operator’s under-
standing of the situation and result
in better use of the machine.
Note or hint on correct procedure in
order to avoid damage to the
environment.
Equipment and features
This instruction manual may refer to
several models with different
features. Components that are not
installed on all models and related
applications are marked with an
asterisk (*). Such components may
be available as special accessories
from your STIHL dealer.
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. If the
operating characteristics or the
appearance of your machine differ from
those described in this manual, please
contact your STIHL dealer for
assistance.
Therefore some changes, modifications
and improvements may not be covered
in this manual.
Guide to Using this Manual

3BR 420
English
Special safety
precautions must be
observed when working
with the power tool.
It is important that you
read, fully understand and
observe the following
safety precautions and
warnings. Keep this
instruction manual in a
safe place for later reference. Non-
observance of the safety precautions
may result in serious or even fatal injury.
Always observe local safety regulations,
standards and ordinances.
If you have never used this power tool
model before:
Have your dealer or other experienced
user show you how to operate your
blower or attend a special training
course in blower operation.
Minors should never be allowed to use a
power tool.
Bystanders, especially children, and
animals should not be allowed in the
area where a power tool is in use.
When the machine is not in use (work
break), shut it off so that it does not
endanger others and secure it against
unauthorized use.
The operator is responsible for avoiding
injury to third parties or damage to their
property.
Do not lend or rent your power tool
without the instruction manual. Be sure
that anyone using your power tool
understands the information contained
in this manual.
You must be rested, healthy and in good
physical condition to operate a power
tool.
Persons with pacemakers only: The
ignition system of your unit produces an
electromagnetic field of a very low
intensity. This field may interfere with
some pacemakers. To reduce health
risks, STIHL recommends that persons
with pacemaker consult their physician
and the pacemaker manufacturer before
operating this tool.
Do not operate this power tool while
under the influence of any substance
(drugs, alcohol) which might impair
vision, dexterity or judgment.
This blower is designed for clearing
leaves, grass, paper, light snow and
similar materials in yards, gardens,
sports stadiums, parks or driveways. It is
also suitable for blow-sweeping forest
paths.
Do not use your blower for any other
purpose since this may result in
accidents or damage to the machine.
Never attempt to modify your blower in
any way since this may also result in
accidents or damage to the machine.
Only mount parts and accessories that
are explicitly approved for this power
tool model by STIHL or are technically
identical. If you have any questions in
this respect, consult a specialist dealer.
To reduce the risk of accidents or
damage to the machine, use only high
quality tools and replacement parts.
STIHL recommends the use of STIHL
original tools and accessories. The
characteristics of these components are
specifically designed to match your
machine and meet your performance
requirements.
Safety Precautions and
Working Techniques

4
English
BR 420
Clothing and Equipment
Wear proper protective clothing and
equipment.
Clothing must be sturdy
but allow complete
freedom of movement.
Wear snug-fitting clothing,
an overall and jacket
combination, do not wear
a coat.
Avoid loose-fitting jackets,
scarves, neckties,
jewellery or anything that
could get into the air
intake. Tie up and confine
long hair (e.g. with a hair
net, cap, hard hat, etc.).
Wear sturdy shoes with non-slip soles.
Wear safety glasses and
sound barriers (ear
plugs or earmuffs) to
protect your hearing.
Wear heavy-duty gloves, preferably
made of leather.
STIHL offers a comprehensive range of
safety clothing and equipment.
Transporting the Unit
Always stop the engine.
Transporting in a vehicle:
Properly secure your unit to prevent
turnover, fuel spillage and damage.
Fueling
Gasoline is an
extremely flammable
fuel. Keep clear of naked
flames and fire. Do not
spill any fuel – do not
smoke.
Always shut off the engine before
refueling.
Do not fuel a hot engine – fuel may spill
and cause a fire.
Always remove the unit from your back
and put it on the ground before fueling.
Fuel the unit only when it is standing
securely on the ground.
Open the fuel cap carefully to allow any
pressure build-up in the tank to release
slowly and avoid fuel spillage.
Fuel your power tool in a well-ventilated
area, outdoors only. If you spill fuel, wipe
the machine immediately – if fuel gets on
your clothing, change immediately.
After fueling, tighten the
fuel filler cap as securely
as possible. This reduces
the risk of unit vibrations
causing the fuel cap to
loosen or come off and
spill quantities of fuel.
To reduce the risk of serious or fatal
burn injuries, check for fuel leakage. If
fuel leakage is found, do not start or run
the engine until leak is fixed.

5BR 420
English
Before Starting
Check that your power tool is properly
assembled and in good condition – refer
to appropriate chapters in the instruction
manual:
– Throttle trigger must move freely
and spring back to idle position
when released.
– Setting lever must move easily to
STOP or 0.
– Check that spark plug boot is secure
– a loose boot may cause arcing
that could ignite combustible fumes
and cause a fire.
– Never attempt to modify the controls
or safety devices.
To avoid the risk of accidents and
personal injury, do not operate your unit
if it is not in a safe operating condition.
Be prepared for an emergency:
Practise quickly opening the fastener on
the waist belt, loosening the shoulder
straps and setting down the unit.
Starting the Engine
Start the engine at least 3 meters from
the fueling spot, outdoors only – not in
confined spaces.
Your power tool is a one-person unit. Do
not allow other persons to be near the
running unit – even when starting.
Do not drop start the engine. The correct
starting procedure is described in your
instruction manual.
Place the unit on firm ground or other
solid surface in an open area. Make sure
you have good balance and secure
footing. Hold the unit securely.
Note: As soon as the engine starts, the
air flow may throw small objects (e.g.
stones) in your direction.
Holding and Controlling the Unit
The unit is carried as a backpack. Hold
and guide the blower tube with your right
hand on the control handle.
Work at a slow walking pace, forwards
only – make sure you have a good view
of the nozzle outlet at all times. To
reduce the risk of tripping or stumbling,
do not walk backwards.
Always shut off the engine before taking
the unit off your back.

6
English
BR 420
During Operation
To reduce the risk of injury, never aim the
airstream in the direction of bystanders
since the air flow can blow small objects
at great speed.
In the event of impending danger or in
an emergency, switch off the engine
immediately by moving the setting lever
to STOP or 0.
Always shut off the engine before
leaving the unit unattended.
Take special care in slippery conditions
– damp, snow, ice, on slopes, uneven
ground, etc.
Watch out for obstacles: Roots, ditches,
holes or rubbish which could cause your
to trip or stumble.
Be particularly alert and cautious when
wearing hearing protection because
your ability to hear warnings (shouts,
alarms, etc.) is restricted.
To reduce the risk of accidents, take a
break in good time to avoid tiredness or
exhaustion.
Work calmly and carefully – in daylight
conditions and only when visibility is
good – ensure you do not endanger
others – stay alert at all times.
After finishing work, put the unit down on
a level, non-flammable surface. To
reduce the risk of fire, do not put it down
near easily combustible materials (e.g.
wood chips, bark, dry grass, fuel).
Mufflers with a catalytic converter can
become particularly hot.
Your power tool produces
toxic exhaust fumes as
soon as the engine is
running. These fumes
may be colorless and
odorless. Never run the
engine indoors or in poorly ventilated
locations, even if your model is equipped
with a catalytic converter.
To reduce the risk of serious or fatal
injury from breathing toxic fumes,
ensure proper ventilation when working
in trenches, hollows or other confined
locations.
The dusts produced during operation
may be dangerous to health. If the work
area is very dusty, wear a respirator.
To reduce risk of fire, do not smoke
while operating or standing near your
power tool. Note that combustible fuel
vapor may escape from the fuel system.
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, have the
machine checked by your servicing
dealer.

7BR 420
English
Using the vacuum attachment*
Warning!
To reduce the risk of
personal injury from fire,
never attempt to pick up
hot or burning substances
(e.g. smoldering ashes,
glowing cigarettes).
To reduce the risk of fatal
injury from fire or
explosion, never attempt
to pick up combustible
fluids (e.g. gasoline) or
any materials soaked in
combustible fluids.
* see “Guide to Using this Manual”
Vibrations
Prolonged use of the unit 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)
–breaks
The period of usage is shortened by:
– Any personal tendency to suffer
from poor circulation (symptoms:
frequently cold fingers, itching).
– Low outside temperatures.
– Gripping force (a tight grip hinders
circulation).
Continual and regular users should
monitor closely the condition of their
hands and fingers. If any of the above
symptoms appear, seek medical advice.
Maintenance and repairs
The machine must be serviced regularly.
Do not attempt any maintenance or
repair work not described in your
Owner’s Manual. All other work should
be carried out by a servicing dealer.
STIHL recommends that maintenance
and repair work be carried out only by
authorized STIHL dealers. STIHL
dealers receive regular training and are
supplied with technical information.
Use only high-quality replacement parts,
in order to avoid the risk of accidents or
damage to the machine. Contact a
dealer if in doubt.
STIHL recommends the use of genuine
STIHL spare parts. Such parts have
been optimized for the machine and the
user's requirements.
Before starting any maintenance or
repair work and before cleaning the
machine, always stop the engine and
disconnect the spark plug boot to
avoid all risk of injury if the engine
starts up inadvertently. – Exception:
adjustment of carburetor and idle speed.

8
English
BR 420
Do not service or store the machine near
a naked light – risk of fire due to the
fuel.
Check fuel cap regularly for tightness.
Use only the spark plugs approved by
STIHL – see Specifications.
Inspect ignition lead (insulation in good
condition, secure connection).
To reduce the risk of fire due to ignition
outside the cylinder, move the slide
control / stop switch to STOP or 0before
turning the engine over on the starter
with the spark plug boot removed or the
spark plug unscrewed.
Check that the muffler is in perfect
working condition.
Do not use the machine if the muffler is
damaged or missing – risk of fire! –
Hearing damage!
Do not touch the hot muffler – risk of
burns!
The condition of the anti-vibration
buffers influences the machine's
vibrations – they must be examined
regularly.

9BR 420
English
Mounting the Elbow
A combination wrench and carburetor
screwdriver are stowed on the underside
of the blower.
The throttle cable is already
connected and must not be kinked
during assembly.
:Push the elbow (1)into the stub (2)
as far as it will go – the stops on the
elbow and fan housing stub must
line up.
: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.
:Secure the throttle cable (4) to the
pleated hose with the retainer (5).
Mounting Blower Tube with
Straight Nozzle*
Operate the machine only with the
blower tube and nozzle properly
mounted.
:Push the blower tube (6) into the
pleated hose (7).
:Push the nozzle (8) onto the blower
tube (6) to position ’a’ (long) or ’b’
(short), as far as lug (9), and rotate
it in the direction of the arrow
(clockwise) to lock.
* see "Guide to Using this Manual"
:Rotate the pleated hose (7)
counterclockwise as far as stop and
leave it in that position.
:Turn the control handle (10)
counterclockwise to the horizontal
position and tighten down the clamp
screw (11).
Assembling the Blower
353BA002 KN
23
1
373BA033 KN
7
4
8
10
6
11
5
9a
b

10
English
BR 420
Mounting Blower Tube with
Curved Nozzle*
Operate the machine only with both
blower tubes properly mounted.
:Push the blower tube (6) into the
pleated hose (7).
:Push blower tube (12) onto blower
tube (6) to position ’a’ (long) or ’b’
(short), as far as lug (9), and rotate
it in the direction of the arrow
(clockwise) to lock.
:Fit the nozzle (13) on the end of the
blower tube (12) and rotate it
clockwise to engage the bayonet
coupling.
* see "Guide to Using this Manual"
:Rotate the pleated hose (7)
counterclockwise as far as stop and
leave it in that position.
:Turn the control handle (10)
counterclockwise to the horizontal
position.
:Rotate the complete blower tube
assembly until the nozzle discharge
opening points in the same direction
as the control handle.
:Tighten down the clamp screw (11).
Adjusting the Control Handle
:Put the unit on your back.
:Loosen the clamp screw (11).
:Slide the control handle (10) along
the pleated hose to the most
comfortable position.
:Tighten down the clamp screw (11).
373BA039 KN
7
12
10
6
11 9ab
13
11
10
373BA002 KN

11BR 420
English
Adjusting the Harness Straps
:Pull the ends of the straps
downward to tighten the harness.
Loosening the Harness Straps
:Lift the tabs of the two sliding
adjusters.
:Adjust the straps so that the
backplate is held firmly and
comfortably against your back.
Your engine requires a mixture of
gasoline and engine oil.
For health reasons, avoid direct skin
contact with gasoline and avoid inhaling
gasoline vapor.
STIHL MotoMix
STIHL recommends the use of STIHL
MotoMix. This ready-to-use fuel mix
contains no benzol or lead, has a high
octane rating and ensures that you
always use the right mix ratio.
STIHL MotoMix is specially
formulated for use in STlHL engines
and guarantees a long engine life.
MotoMix is not available in all markets.
Mixing Fuel
Unsuitable fuels or lubricants or mix
ratios other than those specified
may result in serious damage to the
engine. Poor quality gasoline or
engine oil may damage the engine,
sealing rings, hoses and the fuel
tank.
Gasoline
Use only high-quality brand-name
gasoline with a minimum octane rating
of 90 – leaded or unleaded.
If your machine is equipped with a
catalytic converter, you must use
unleaded gasoline.
A few tankfuls of leaded gasoline
will greatly reduce the efficiency of
the catalytic converter.
Engine Oil
Use only quality two-stroke engine oil.
We recommend STIHL two-stroke
engine oil since it is specially
formulated for use in STlHL engines
and guarantees a long engine life.
If STIHL two-stroke engine oil is not
available, use only quality two-stroke oil
designed for use in air cooled engines.
Do not use oils designed for water
cooled engines or engines with a
separate lubricating system (e.g.
conventional four-stroke engines).
Use only STIHL 50:1 two-stroke
engine oil for the fuel mix in models with
a catalytic converter.
373BA003 KN
373BA004 KN
Fuel

12
English
BR 420
Mix Ratio
STIHL 50:1 two-stroke engine oil:
50 parts gasoline to 1 part oil
Other high-quality two-stroke engine
oils:
25 parts gasoline to 1 part oil
Examples
:Use a canister approved for storing
fuel. Pour oil into the canister first,
then add gasoline and mix
thoroughly.
Storing Fuel
Store fuel only in approved safety-type
fuel canisters in a dry, cool and safe
location protected from light and the sun.
Fuel mix ages:
Only mix sufficient fuel for a few weeks
work. Do not store fuel mix for longer
than 3 months.
Exposure to light, the sun, low or high
temperatures can quickly make the fuel
mix unusable.
:Thoroughly shake the mixture in the
canister before fueling your
machine.
Pressure may build up in the
canister – open it carefully.
:Clean the fuel tank and canister
from time to time.
Dispose of remaining fuel and
cleaning fluid properly in
accordance with local regulations
and environment requirements.
:Before fueling, clean the filler cap
and the area around it to ensure that
no dirt falls into the tank.
:Position the unit so that the filler cap
is facing up.
Take care not to spill fuel while fueling
and do not overfill the tank.
After fueling, tighten down filler cap
by hand as securely as possible.
Gaso-
line
STIHL
engine oil
50:1
Other high-
quality two-
stroke engine
oils:
25:1
Liters Liters (cc) Liters (cc)
1 0.02 (20) 0.04 (40)
5 0.10 (100) 0.20 (200)
10 0.20 (200) 0.40 (400)
15 0.30 (300) 0.60 (600)
20 0.40 (400) 0.80 (800)
25 0.50 (500) 1.00 (1000)
Fueling
373BA006 KN

13BR 420
English
Change the fuel pickup body
once every year
:Drain the fuel tank.
:Use a hook to pull the fuel pickup
body out of the tank and take it off
the hose.
:Push the new pickup body into the
hose.
:Place the pickup body in the tank.
With the engine stopped and before
starting, check the air intakes
between the backplate and
powerhead for blockages and clean
if necessary.
A protective screen is available as a
special accessory to keep the air
intakes clear.
Only machines with catalytic
converter
:Move the setting lever to idle
position.
Machines with a catalytic converter must
always be switched off with the setting
lever in the idle position because the
throttle cable will otherwise disconnect
itself from the throttle trigger.
The throttle cable reconnects itself
automatically when the setting lever is
moved to the idle position.
:Observe safety precautions – see
chapter “Safety Precautions and
Working Techniques”.
:Slide the stop switch (1) to #
:Move the setting lever (2) to the
center position – this is the
starting throttle position
Note:
The setting lever can be used to select
any throttle opening between idle speed
(lower stop) and full throttle (upper stop).
Set the lever to idle position before
switching off the engine.
373BA007 KN
Information
Before You Start
373BA037 KN
Starting / Stopping
the Engine
373BA008 KN
1
373BA009 KN
2

14
English
BR 420
:If the engine is cold, turn the choke
knob to g
:If the engine is warm, turn the
choke lever to e
Also use this position if the engine
has been running but is still cold.
:Put the unit on the ground. Check
that bystanders are well clear of the
general work area and the nozzle.
: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.
:Pull the starter grip slowly with your
right hand until you feel it engage
and give it a brisk strong pull. Do not
pull the starter rope out all the way
as 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.
373BA010 KN373BA011 KN
373BA012 KN

15BR 420
English
When engine begins to fire:
:If engine is cold:
Turn choke knob to e and continue
cranking until engine runs.
:If engine is warm:
Continue cranking until engine runs.
As soon as engine runs:
:Move the setting lever (2) to the
lower stop so that the engine settles
down to idle speed.
To shut down the engine:
:Slide the stop switch (1) to $
At very low outside temperatures:
Allow engine to warm up
As soon as engine runs:
:Move the setting lever to the lower
stop – the engine settles down to
idle speed.
:Open throttle slightly – warm up
engine for a short period.
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.
:Pull off the spark plug boot.
:Unscrew and dry off the spark plug.
:Set the stop switch to 0
:Open the throttle fully.
:Pull the starter rope several times to
clear the combustion chamber.
373BA013 KN
373BA014 KN
2
1
373BA015 KN
373BA016 KN

16
English
BR 420
:Fit the spark plug and reconnect the
spark plug boot.
:Move the stop switch to #
:Turn the choke knob to e
even if the engine is cold.
:Now start the engine.
Fuel tank run until dry and then
refueled
:Pull the starter rope several times to
prime the fuel line.
During break-in period
A factory new machine should not be run
at high revs (full throttle off load) for the
first three tank fillings. This avoids
unnecessary high loads during the
break-in period.
As all moving parts have to bed in during
the break-in period, the frictional
resistances in the engine are greater
during this period.
The engine develops its maximum
power after about 5 to 15 tank fillings.
During operation
After a long period of full-throttle
operation, allow engine to run for a while
at idle speed so that the heat in the
engine can be dissipated by flow of
cooling air. This protects engine-
mounted components (ignition,
carburetor) from thermal overload.
After finishing work
Storing for short period:
Wait for engine to cool down. Drain the
fuel tank and keep the unit in a dry place,
away from sources of ignition, until you
need it again.
Storing for a long period:
see chapter "Storing the Machine".
Dirty air filters reduce engine power
increase fuel consumption and make
starting more difficult.
If there is a noticeable loss of engine
power
:Turn choke knob to g
:Release the screws (1) and pull
off the filter cover (2).
Operating Instructions Cleaning the Air Filter
1
373BA017 KN
2
1

17BR 420
English
: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 when
you change the main filter.
:Take the prefilter (4) out of the filter
cover.
:If the prefilter is wet, dry it – then
knock it out on the palm of your
hand or blow out with compressed
air.
:Always replace a damaged prefilter.
:Clean loose dirt from the filter cover
and filter chamber.
:Install the main filter and prefilter
elements in the filter cover.
:Fit the cover on the filter base (5)
and tighten it down firmly.
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
correct the adjustment of the high speed
and low speed screws within fine limits.
373BA018 KN
3
45
Adjusting the Carburetor

18
English
BR 420
Standard Setting
:Shut off the engine.
:Check the air filter and clean or
replace if necessary.
:Check the spark arresting screen (if
fitted) in the muffler and clean or
replace if necessary.
:Carefuly turn both adjusting screws
counterclockwise as far as stop:
High speed screw (H) is now open
1/4 turn
Low speed screw (L) is now open
1/4 turn
:Start and warm up the engine.
Adjusting Idle Speed
Engine stops while idling
:Turn the idle speed screw (LA)
clockwise until the engine runs
smoothly.
Erratic idling behavior, engine stalls
even after re-adjusting LA screw,
poor acceleration
Idle setting is too lean:
:Turn low speed screw (L)
counterclockwise – no further than
stop – until the engine runs and
accelerates smoothly.
Erratic idling behavior
Idle setting is too rich:
:Turn low speed screw (L) clockwise
– no further than stop – until the
engine runs and still 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).
Fine tuning for operation at high
altitude
A slight correction of the setting may be
necessary if engine power is not
satisfactory:
:Check standard setting.
:Warm up the engine.
:Turn the 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.
HL
373BA043 KN
LA
L
373BA044 KN

19BR 420
English
Power tools with a catalytic converter*
may only be operated with unleaded
gasoline and STIHL two-stroke
engine oils in a mix ratio of 50:1
(see chapter “Fuel”).
The catalytic converter in the muffler
reduces noxious emissions in the
exhaust gas.
Correct adjustment of the carburetor
(if adjustable) and observance of the
specified mix ratio of gasoline and two-
stroke engine oil are essential to
minimize harmful exhaust emissions
and ensure a long catalyst service life.
* see “Guide to Using this Manual”
If engine is down on power, difficult to
start or runs poorly at idle speed, first
check the spark plug.
:Remove the spark plug –
see "Starting / Stopping the Engine".
:Clean dirty spark plug.
:Check electrode gap (A) and
readjust if necessary – see
"Specifications".
:Rectify the problems which have
caused fouling of spark plug:
– To much oil in fuel mix.
– Dirty air filter.
– Unfavorable running conditions.
: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 "Specifications".
To reduce the risk of arcing
and fire:
:If the spark plug comes with a
detachable adapter nut (1), screw it
on firmly.
Catalytic Converter* Checking the Spark Plug
000BA002 KN
1
000BA045 KN