CONTENTS. Honda UMK 422, UMK 431

 HONDA
Equipment
Owner's Manual
TRIMMER/BRUSH CUTTER
UMK422 « UMK431
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©2003 American Honda Motor Co., Inc. All Rights Reserved
А WARNING: А
The engine exhaust from this product
contains chemicals known to the State of
California to cause cancer, birth defects, or
other reproductive harm.
Keep this owner's manual handy, so you can refer to it at any time. This owner's manual is considered a
permanent part of the trimmer/brush cutter and should remain with the trimmer/brush cutter if resold.
The information and specifications included in this publication were in effect at the time of approval for
printing. Honda Motor Co., Ltd. reserves the right, however, to discontinue or change specifications or
design at any time without notice and without incurring any obligation whatever. No part of this
publication may be reproduced without written permission.
INTRODUCTION
Congratulations on your selection of a Honda trimmer/brush cutter. We are certain you will be pleased
with your purchase of one of the finest trimmers/brush cutters on the market.
We want to help you get the best results from your new trimmer/brush cutter and to operate it safely.
This manual contains the information on how to do that; please read it carefully.
As you read this manual, you will find information preceded by a [NOTICE symbol. That information i is
intended to help you avoid damage to your trimmer, other property, or the environment.
We suggest you read the warranty policy to fully understand its coverage and your your responsibilities
of ownership. The warranty policy is a separate document that should have been given to you by your
dealer.
When your trimmer/brush cutter needs scheduled maintenance, keep in mind that your Honda servicing
dealer is specially trained in servicing Honda trimmers/brush cutters. Your Honda servicing dealer is -
dedicated to your satisfaction and will be pleased to answer your questions and concerns.
Best Wishes,
Honda Motor Co., Ltd.
INTRODUCTION
A FEW WORDS ABOUT SAFETY
Your safety and the safety of others are very important. And using this trimmer/brush cutter safely is an
important responsibility.
To help you make informed decisions about safety, we have provided operating procedures and other
information on labels and in this manual. This information alerts you to potential hazards that could hurt
you or others.
Of course, it is not practical or possible to warn you about all the hazards associated with operating or
maintaining a trimmer/brush cutter. You must use your own good judgment.
You will find important safety information in a variety of forms, including:
e Safety Labels — on the trimmer/brush cutter.
e Safety Messages — preceded by a safety alert symbol /\ and one of three signal words, DANGER,
WARNING, or CAUTION.
These signal words mean:
FO You WILL be KILLED or SERIOUSLY HURT if you don't follow instructions.
NUI [NES You CAN be KILLED or SERIOUSLY HURT if you don't follow instructions.
A CAUTION You CAN be HURT if you don’t follow instructions.
o Safety Headings — such as IMPORTANT SAFETY INFORMATION.
e Safety Section — such as TRIMMER SAFETY.
e Instructions — how to use this trimmer/brush cutter correctly and safely.
This entire book is filled with important safety information — please read it carefully.
CONTENTS
TRIMMER SAFETY ..........e...en.neveanooaeanonaonanantocono 4
IMPORTANT SAFETY INFORMATION .............. SR
ATTACHMENTS 8 MODIFICATIONS ..................—....... .....5
Attachments ….…..….…........……….…essercanceecanesncces arena EEE SA 5
Modifications ........................eeeeseeeer e eee De ee. 5
IMPORTANT MESSAGE TO EMPLOYERS ................... 5
SAFETY LABEL LOCATIONS eneranvonvoreavenernanecocra encerrar. 6
RECOMMENDED CUTTING ATTACHMENTS ... 7
CUTTING-LINE HEADS AND SHIELD ...................e..... 7
Manuai-Feed Cutting-Line Head ..............-.................. nenenno. 7
Semiautomatic (bump-feed) Cutting-Line Head cocranceananseaneu se 7
BLADES AND SHIELD. ........ erneoarenoeniconeaneaacrnaeoart no nereeeccen es 8
Grass/Weed Blades ....................e=.e..0067érreneereceneoconcen В
Weed/Brush Blades .............................er+mmececereconerenacenecar ere. 8
Brush/Wood Blades ......................-.eeonececriceneceninen GGG verona 8
CUTTING ATTACHMENT APPLICATIONS ...........ccc...... 9
CONTROLS 8: EQUIPMENT ..................en=e=.. 10
COMPONENT 8: CONTROL LOCATIONS peoucentananenenem 10
CONTROLS -..............eeeeceu0cecaorerricaanecorenenceme aassrrecaena nan ee 11
Choke Lever .................... e... cesenccaracacanenoeantoneannonemea 11
ignition Switch ......................e...00=mmeenererrcen sanan ee non. 11
Operator Presence Léever .....................-.emeerrcrrmerne 11
Throttle Trigger ...............---....eneenmneconeornere ero ener renneooene nene. 11
Throttle Set BUttOn .…............….…...…..…..conserencessranaennansecaanrensanes 12
Priming BUID ..…..….....……urerrecrerrrnrensaerserancencencanerancencencns 12
Recoil Starter Grip .…..….......…............…….…srerceraoccarsensantenensasceurs 12
EQUIPMENT ores 13
Shoulder Harness ......................e.e=iecrerreerieirc rear eZ 13
Safety Glasses .......................e...eereccronoconccnnc anar eereteen eee 13
BEFORE OPERATION .............. cnsonocanenanadnaaaones 14
ARE YOU READY TO OPERATE THE TRIMMER? ........ 14
Knowledge ............:-.e---ee=meescercaocos recon vanentarenocene nene enendcer rene. 14
Physical and Mental Readiness ......................c...2e===e000enmoa0 14
Protective Clothing ....................ew.=.=.e-e.e0000mei eZ 14
IS YOUR WORKING AREA READY? ......................e.. 14
IS YOUR TRIMMER READY TO GO? .................e.... „15
Safety Inspection........ eounooonanoconereeareacoanonereer once nene enrneececarece 15
Cutting Attachment inspection CE eonenenonennnn. 15
Maintenance Inspection .......................... cnvanentencessrennencenvane 15
ARE YOUR SHOULDER HARNESS AND
TRIMMER CORRECTLY ADJUSTED? ...................eeccc. 16
Adjusting the Hamness ......................eseecerrerveresneccorneeneren ens 16
Balancing the Trimmer on the Shoulder Harness eben a EEG ERBE 16
OPERATION …….….………corerscuseenmansenseenmencennenence 17
SAFE OPERATING PRECAUTIONS . Ceerrrrerenreretretaennennans 17
STARTING THE ENGINE ..................eanm.eseeeme. een .17
STOPPING THE ENGINE ..............e.eneemmesesmeccrcicanneóoee 19
- TRIMMER/HARNESS QUICK DISCONNECTION. ........ 19
TRIMMER OPERATION............ anenareaooreneoenerearenecareeeananes 19
— Operating Position .........................e+meneecae o oe 19
Throttle Operation ................... e... eee 20
Using a Nylon Cutting-Line Head ....................—...........eemmeen.. 20
Using Blades ................e.....e.erenecrconeeracooecarnacaontenanoneencenenctacaa 21
SAFE OPERATING PRACTICES ..................emeernecaaanno. 21
Thrown Debris ............-...e...e..eec0ccescacccocnarooconeounenerneenaaarencen 21
Blade Thrust (Kickback) ...........................0.00000rcs00ereenicooce 22
OPERATING TIPS ..................ce.a..e0occcconennenoonerecenonceeenee. 22
SCYTNING ee rReenenrenen econo nerneceonoes 22
OPERATION(continued)
Trimming and Edging .............. eononoacancocanvacace eianenncnonceneecoreneee 23
Brush Clearing ........................... eeneocaaneeiononennoncanen soe eecoeoonene. 23
Operation on Slopes ..............e.......reemeeerreeneraeenenen rennen 23
SERVICING YOUR HONDA TRIMMER ........... 24
THE IMPORTANCE OF MAINTENANCE ..................... 24
MAINTENANCE SAFETY ovine, nenennananono OÙ
MAINTENANCE SCHEDULE ......................-.eecneecenccrnreos 25
ENGINE ….…...…..……rerrsccarraserreenserersennennene eeoonoocenTntrbanencece 26
Engine Oil Level Check .. pnennanenoes Mannoceoroo ana o oneoneenrreanecens ….. 26
Engine Oil Change ............ Manecaacenenenreceanaeeraraarnesnnrecencocerreece. 26
Engine Oil Recommendations ........... enneacancacaee SA 27
- Air Filter Inspection OA 27
Air Filter Cleaning .................... ==... proneoacorenenoe errr 27
Spark Plug Service ....................e-ee=...mmeencanerrenconenenennencanenanees 28
Spark Arrester Service ...........................enereerereorcartenene e... 29
Cooling Fin inspection ..................—.....eee=emrenrcerierneire Dee 30
Throttle Cable Inspection EEE creas 30
Throttle Cable Adjustment .......................=—..——.—.erescenaucenecenoen 30
FUEL SYSTEM .........c.een.errescreanos ETE
Refueling ...............=.eeeccermeercenree rene STR 31
Fuel Recommendations ..................-—.eeceererinene nn 31
Fuel Tube Inspection .....................e...e.e=merrmeereneneea e 32
Fuel Filter and Fuel Tank Cleaning ....................-.—.—ew=...—.... 32
CUTTING ATTACHMENTS................... eneeoronenoarenceneneaeme 33
Cutting-Line Heads ............................xeerirconnecere eee 33
Blades ...............e-.—-eeomneerieneneeneon. PND 39
STORAGE ..........mennennacanevaroonenancasocorcenananenananene 41
STORAGE PREPARATION cssscesaveemuresensnnnennepenca ere c eee 41
ClBaNING ……....…..…...…....….….crersertencennsenssenrec an Deere 41
Fuel ..............emmzocarocosooneuoacaanacooneconrenenermeneacooocenen aaa ssn nesses ss 41
Engine Of essen HEERES aeennencanos eonnaceos 42
Carburetor & Air Cleaner ....... etre ees tee res aaa r rests e sees area sane soe 42
Blade este een eaenaiaooenoaoecanee ener ereneaecacan ren nececana 42
Engine Cylinder ........................-—....——... eee nene 42
STORAGE PRECAUTIONS ...................eeeconneconnenenennonene 42
REMOVAL FROM STORAGE .............eeeeecsnccociconscaceeves 42
TRANSPORTING ................ A 43
TAKING CARE OF UNEXPECTED PROBLEMS ....44
STARTING PROBLEMS ............. enorconeacocenacenarocancanananene 44
ENGINE OPERATING PROBLEMS .................evmeenooones 44
CUTTING HEAD PROBLEMS...........................enecceocarnees 45
TECHNICAL 8: CONSUMER INFORMATION .. . 46
TECHNICAL INFORMATION -......................eonernenarnercons 46
Serial Number Locations ....................e==es+>ecoonensconeoranenr coa 46
Carburetor Modification for High Altitude Operation censaeuennne ‚46
Oxygenated Fuels ......................ereeemcren eee 47
Emission Control System Information ......................=...—.... 48
Specifications ......................ee=resresesene e ee eee 49
CONSUMER INFORMATION ers RER 51
Honda Publications ................e....e.e....eeeeeercesneneeo o eee 51
Warranty Service Information .......................-......es0sereniceene 51
QUICK REFERENCE
INFORMATION. ....................... Inside back cover
TRIMMER SAFETY
IMPORTANT SAFETY INFORMATION
Honda UMK422 and UMK431 trimmers/brush
cutters are designed to cut grass, weeds, brush,
and/or wood if equipped with an appropriate
cutting attachment. Other uses can result in injury
to the operator or damage to the trimmer and
other property.
These Honda trimmers are intended for use by
gardening professionals. Never allow children to
operate the trimmer.
Most accidents can be prevented if you follow all
instructions in this manual and on the trimmer.
The most common hazards are discussed below,
along with the best way to protect yourself and
others.
Always Wear Eye Protection and Protective
Clothing
e The most frequent injuries associated with
string trimmers are eye injuries caused by
thrown debris. Always wear safety glasses or
goggles that meet the ANSI Z87.1 rating
whenever you use the trimmer.
e The operator must wear hearing protectors
when using this trimmer. Hearing protectors
will protect the operator's ears from noise
damage.
e Wearing protective clothing also reduces the
risk and severity of injury from thrown debris or
contact with the cutting attachment. Wear the
trimmer harness, gloves, a long-sleeved shirt,
long pants, and sturdy boots with nonslip
soles.
See page 14 for more information.
Keep Away From Cutting Lines and Blades
e A spinning cutting attachment can cut through
your clothes and skin just as easily as it cuts
through grass and brush. Keep all parts of your
body away from a spinning cutting attachment.
e Even after the engine has stopped, the cutting
attachment will spin for several seconds. Do
not touch it until it has stopped spinning, or you
may get cut.
Turn the Engine Off When Not Trimming
e If you stop trimming or cutting for any reason,
even to clean off the cutting attachment,
always shut off the engine.
Keep People Away From Your Working Area
e To prevent injury to others, keep.people at
least 50 feet (15 meters) away from the
working area during operation.
Always Wear the Harness When Trimming
o The harness keeps the trimmer away from
your body, lowering your chances of being cut
by the trimmer’s blade or cutting line.
Read This Manual Before Using the Trimmer
e Read the manual before operating the trimmer.
Understand how to use all the controls and
obey all warnings.
Clear the Working Area First
e Objects thrown by the trimmer can cause
serious injury. Before operating the trimmer,
carefully inspect the area, and remove all
broken glass, pieces of wire, and other loose
objects.
Keep the Trimmer Properly Maintained
e The cutting attachment should be examined for
looseness, cracks, broken parts, or excessive
wear. Tighten or replace as needed before
operating the trimmer.
e Do not operate the trimmer without a debris
shield properly installed. Make sure you have
the right shield installed for your cutting
attachment.
For more information, see page 9.
TRIMMER SAFETY
ATTACHMENTS & MODIFICATIONS
Modifying your trimmer/brush cutter, or installing
some non-Honda attachments, can make your
trimmer unsafe. Before you make any
modifications or install any attachments, be sure
to read the following information.
Attachments
Your Honda trimmer servicing dealer has cutting
attachments, debris shields, barrier bars, handles,
handlebars, and shoulder harnesses that have
been designed and approved for your trimmer
and are covered by warranty.
Non-Honda attachments are usually designed for
universal applications. Although aftermarket
attachments may fit on your trimmer, they may
not meet factory specifications and could make
your trimmer unsafe.
Modifications
Do not remove the debris shield or modify your
trimmer in any way that would alter its design or
operation. This could make your trimmer unsafe.
IMPORTANT MESSAGE TO EMPLOYERS
As an employer, you have special responsibilities
to the people who work for you.
Before you ask anyone to operate this trimmer/
brush cutter, you need to determine whether the
person is old enough, large enough, and strong
enough to safely handle and control the trimmer/
brush cutter.
If you decide they are, make sure the employee
reads and understands all instructions and
warnings in this manual and on the labels before
operating the trimmer/brush cutter.
Allow adequate time for hands-on training by a
qualified instructor, and personally supervise
practice sessions, until you feel sure the
employee is ready to operate the trimmer/brush
cutter.
Also be sure employees wear proper clothing, eye
and hearing protection, and any other gear that
may be required by local ordinances or your
insurance company.
Remember, too, that you are responsible for
keeping the trimmer/brush cutter properly
maintained and in safe operating condition.
Your commitment to safety on the job can help
prevent accidents and result in longer and more
productive years of service.
TRIMMER SAFETY
SAFETY LABEL LOCATIONS
The labels shown here contain important safety information. Please read them carefully. These labels
are considered permanent parts of your trimmer/brush cutter. If a label comes off or becomes hard to
read, contact an authorized Honda servicing dealer for a replacement.
A WARNING
READ AND FOLLOW
OWNER'S MANUAL.
LL] Failure to do so can
—=—1]| result in serious injury
to the operator and
bystanders.
A WARNING
(
©
‘: fom) m a
OBJECTS THROWN BY CUTTING ATTACHMENTS CAN CAUSE
SERIOUS INJURY.
E Always wear eye protection that meets ANS| 287.1.
E Always wear hearing protection and protective clothing.
В Keep bystanders at least 50 feet (15m) away.
8 Do not operate without shield.
N /
N Ф
<
ES
TYPES EQUIPPED WITH
LOOP HANDLE
A WARNING
CONTACT WITH ROTATING CUTTING ATTACHMENT CAN CAUSE SERIOUS INJURY.
8 Keep away from rotating cutting attachment.
E Be aware of possible kickback when using blades.
(See Owner's Manual for special operating precautions)
E Install proper shield, handle, and harness for cutting attachment.
N Use only Honda recommended cutting attachments.
Se J
y
7
Na
TYPES EQUIPPED WITH
U-TYPE HANDLEBAR
RECOMMENDED CUTTING ATTACHMENTS
CUTTING-LINE HEADS AND SHIELD
A cutting-line head containing nylon monofilament
line, and a debris shield with cutoff knife, is
standard equipment. The shield’s cutoff knife
automatically removes any excess line that is
released from the cutting head.
Honda UMK431UNBA trimmers are supplied with
two different debris shields. Use the debris shield
with the cutoff knife when the cutting-line head is
installed.
Nylon monofilament line is suitable for cutting
grass and ordinary weeds, but not brush and
woody growth.
Manual-Feed Cutting-Line Head
Line is released from the cutting head by
manually pulling and turning the spool with the
trimmer stopped.
Semiautomatic (bump-feed) Cutting-Line Head
Line is released from the cutting head by bumping
the spool on hard ground during operation.
CUTTING-LINE HEAD
NYLON MONOFILAMENT LINE
CUTOFF KNIFE
(inside debris shield)
DEBRIS SHIELD
MANUAL-FEED CUTTING-LINE HEAD
To release more line,
pull spool and turn
counterciockwise.
SEMIAUTOMATIC (bump-feed) CUTTING-LINE HEAD
RECOMMENDED CUTTING ATTACHMENTS
BLADES AND SHIELD
A variety of blades is available from your Honda
trimmer servicing dealer. Always use a debris
shield designed for use with a blade when
attaching a blade to your trimmer. This type of
debris shield does not have a cutoff knife.
Metal blades are supplied with a cover
surrounding the edge of the blade. For safety, and
to protect the blade, the cover should be installed
whenever the trimmer is not in use.
If installing a metal blade on, a Honda trimmer
equipped with a loop handle, also install the
Honda conversion kit that includes a full shoulder
harness, a barrier bar, and a debris shield for
metal blades. Follow the installation instructions
and safety information that come with the kit.
Grass/Weed Blades
Grass/weed blades, which may be plastic or
metal, are used as an alternative to nylon
monofilament line for cutting grass and ordinary
weeds.
However, blades should never be used for edging
against solid surfaces.
Weed/Brush Blades
These metal blades have chisel-shaped teeth that
are used for cutting tough field grass, thick
weeds, and light brush. They are not designed for
sawing woody material. The teeth must be sharp
for good results.
Brush/Wood Blades
These metal blades are used for sawing through
saplings, shrubs, and woody brush. The teeth
must be sharp for good results. Brush/wood
blades will also cut grass and weeds, but they are
not efficient for that purpose.
CUTTING LINE
DEBRIS SHIELD DEBRIS SHIELD
BLADE
DEBRIS
SHIELD
GRASS/WEED BLADE
WEED/BRUSH BLADE
BRUSH/WOOD BLADE
BRUSH/WOOD BLADE
COVER
RECOMMENDED CUTTING ATTACHMENTS
CUTTING ATTACHMENT APPLICATIONS
e . x О Su
| WAS Na A
Nu Der CE
C
GRASS AND LIGHT WEEDS
THICK WEEDS AND LIGHT BRUSH
OK OK OK X
Da
X X OK X
X X X OK
Your Honda trimmer servicing dealer has cutting attachments that have been designed and approved
for your trimmer and are covered by warranty. Non-Honda attachments are usually designed for
universal applications. Although aftermarket attachments may fit on your trimmer, they may not meet
factory specifications and could make your trimmer unsafe.
CONTROLS & EQUIPMENT
COMPONENT & CONTROL LOCATIONS
CHOKE LEVER SPARK PLUG CAP
AIR CLEANER COVER
SPARK ARRESTER
UMK422LNA
UMK422LTA
UMK431LNA
PRIMING BULB
UMK431LTA FUEL RETURN TUBE
(clear)
NG-LIN FUEL TANK CAP
CUTTING-LINE HEAD FUEL SUPPLY TUBE
GEAR CASE (black)
FL LOOP HANDLE |
~~ OIL FILLER CAP
DEBRIS SHIELD WITH — (<= HARNESS HANGER
CUTOFF KNIFE
| THROTTLE SET BUTTON
DRIVE SHAFT "a OPERATOR PRESENCE LEVER
HOUSING S
IGNITION SWITCH
THROTTLE
TRIGGER
UMK431UNBA
(supplied with two
cutting attachments GEAR CASE IGNITION SWITCH
and debris shields) BLADE
THROTTLE
| SET BUTTON
DEBRIS SHIELD THROTTLE ЭЙ
FOR BRUSH/WOOD BLADE TRIGGER 77 ОРЕВАТОВ
= 7 PRESENCE
NN 7 LEVER
DRIVE SHAFT NG HARNESS HANGER
CUTTING-LINE HEAD HOUSING e
U-TYPE
HANDLEBAR
DEBRIS SHIELD WITH
CUTOFF KNIFE
10
CONTROLS & EQUIPMENT
CONTROLS
Choke Lever
The choke lever opens and closes the choke
valve.
The CLOSED position enriches the fuel mixture
for starting a cold engine.
The OPEN position provides the correct fuel
mixture for operation after starting, and for
restarting a warm engine.
Ignition Switch
The ignition switch controls the ignition system.
The ignition switch button must be in the ON (1)
position for the engine to start and run.
Moving the ignition switch button to the OFF (O)
position stops the engine.
Operator Presence Lever
The operator presence lever blocks the throttle
trigger. This safety feature prevents unintentional
throttle operation if the trimmer is bumped while
the operators hand is not on the control handle.
When the operator presses the presence lever by
gripping the control handle, the trigger moves
freely. |
Throttle Trigger
The throttle trigger controls engine speed.
Pulling the throttle trigger toward the grip
increases engine speed. The trimmer will have
the greatest cutting force at maximum engine
speed. |
Releasing the throttle trigger reduces engine
speed. At idle, the cutting-line head or blade
should coast to a stop.
CHOKE LEVER
U-type handle: Loop handle:
"IGNITION SWITCH BUTTON
THROTTLE
TRIGGER
| OPERATOR
IDLE PRESENCE
(cutting LEVER
attachment
stops)
FAST _
(cutting =
attachment
rotates)
11
CONTROLS 8: EQUIPMENT
Throttle Set Button
The throttle set button is used to hold the throttle
trigger at the fast idle position for starting. Do not
allow the cutting line or blade to contact any
obstruction when starting the engine with the
throttle button engaged
To engage the throttle set button, press the
operator presence lever by gripping the control
handle, pull the throttle trigger, then press and
hold the throttle set button while releasing the
throttle trigger.
To disengage the throttle set button, simply pull
the throttle trigger. The throttle set button
automatically disengages when the throttle trigger
is pulled.
Do not use the throttle set button while operating
the trimmer. The trimmer will not return to idle,
and the cutting-line head or blade will continue to
spin, until the set button is disengaged and the
throttle trigger is released.
Priming Bulb
Pressing the priming bulb pumps fuel from the
fuel tank to the carburetor. This procedure is
necessary for starting a cold engine and after
refueling an engine that has run out of fuel.
To ensure that fuel has reached the carburetor,
press the priming bulb repeatedly until fuel can be
seen in the clear-plastic fuel-return tube.
Recoil Starter Grip
Pulling the starter grip operates the recoil starter
to crank the engine for starting.
12
THROTTLE
TRIGGER
OPERATOR
PRESENCE
LEVER
PRIMING BULB ~ FUEL RETURN TUBE
(clear plastic tube)
RECOIL
STARTER
GRIP
CONTROLS & EQUIPMENT
EQUIPMENT
- Honda UMK422 and UMK431 trimmers/brush
cutters are supplied with a shoulder harness and
safety glasses. Refer to page 14 for a description
of other equipment and protective clothing you will
need.
Shoulder Harness
A full shoulder harness must be worn by the
operator of these Honda trimmers/brush cutters
when equipped with a blade and debris shield. If
the trimmer is equipped with a cutting-line head
and shield with cutoff knife, the operator may
wear a single-strap harness.
A suitable shoulder harness is supplied with each
new Honda UMK422 and UMK431 trimmer/brush
cutter. Replacement shoulder harnesses may be
purchased through any authorized Honda
trimmer/brush cutter servicing dealer.
Before operation, adjust your shoulder harness as
described on page 16.
Quick-Release Latch
The shoulder harnesses supplied with these
trimmers are equipped with a quick-release laich.
Pull the latch tab upward to detach the trimmer
from the harness.
Insert the latch tongue in the slot of the quick-
release latch to reattach the trimmer to the
harness.
Safety Glasses
Safety glasses or goggles that comply with ANSI
standard Z87.1 must be worn by the operator of
any Honda trimmer/brush cutter. The safety
glasses supplied with each new Honda UMK422
and UMK431 trimmer/brush comply with the ANSI
standard.
FULL SHOULDER HARNESS
QUICK-RELEASE LATCH
SINGLE-STRAP SHOULDER HARNESS
QUICK-RELEASE LATCH
LATCH TAB
QUICK-RELEASE LATCH
SAFETY GLASSES (ANSI 287.1)
13
BEFORE OPERATION
ARE YOU READY TO OPERATE THE
TRIMMER?
Your safety is your responsibility. A little time
spent in preparation will significantly reduce your
risk of injury.
Knowledge
Read and understand this manual. Know what the
controls do and how to operate them.
Familiarize yourself with the trimmer and its
operation before you begin to use it. Know what
to do in case of emergencies.
Physical and Mental Readiness
You must be alert and in good physical condition
to operate the trimmer. Do not operate the
trimmer if you are tired, ill, or under the influence
of alcohol, medication, or any substance that
might impair your vision, dexterity, or judgment.
If you have any physical problem that may be
aggravated by strenuous work, consult your
physician before operating the trimmer.
Protective Clothing
Wearing protective clothing will reduce your risk
of injury. Do not wear loose clothing, jewelry,
short pants, sandals, or go barefoot. Secure hair
so it is above shoulder level.
Eye, Face, and Head Protection
Always wear safety glasses or goggles that
comply with ANSI standard Z87.1 to protect your
eyes from thrown objects. Prescription glasses
may be worn under the safety glasses or goggles.
A helmet with a face shield is recommended for
further protection. However, safety glasses or
goggles should always be worn under the face
shield. Do not rely on a face shield alone to
protect your eyes.
Wearing a dust mask will help to reduce the
amount of pollens and dust inhaled.
14
Hearing Protection
Hearing protectors will help to protect your ears
from noise. Earmuff-style hearing protectors can
also protect your ears from thrown objects.
Hand and Body Protection
Wear gloves, a long-sleeved shirt, and long pants
made of heavy material. Clothing should fit
closely but allow freedom of movement, and
should have no strings, straps, etc. that could
catch on brush or the trimmer. Keep clothing
fastened.
Foot Protection
Wear sturdy work boots with good toe protection
and nonslip soles.
IS YOUR WORKING AREA READY?
Objects thrown by the trimmer can cause serious
injury. Before operating the trimmer, carefully
inspect the area, and remove all objects that
could be thrown by, or entangled in , the cutting
attachment, such as rocks, broken glass, nails,
wire, or string.
Clear the area of children, bystanders, and pets.
Keep all children, bystanders, and pets at least 50
feet (15 meters) away from where the trimmer is
being operated.
Even outside a 50-foot (15-meter) radius of the
trimmer, there may be a risk of injury from thrown
objects, so bystanders should be encouraged to
wear eye protection.
If anyone approaches you while you are operating
the trimmer, release the throttle trigger and stop
the engine.
BEFORE OPERATION
IS YOUR TRIMMER READY TO GO?
For your safety, and to maximize the service life
of your equipment, it is very important to take a
few moments before you operate the trimmer to
check its condition. Be sure to take care of any
problem you find, or have your servicing dealer
correct it, before you operate the trimmer.
AWARNING |
Improperly maintaining this trimmer, or
failing to correct a problem before
‘operation, could cause a malfunction in
which you could be seriously injured.
Always perform a preoperation inspection
before each operation, and correct any
problem.
Safety Inspection
e Look around the engine for signs of oil or
gasoline leaks. Wipe up any spills before
starting the engine.
e Replace any damaged parts.
e Check that all fasteners are in place and
secure. Tighten as necessary.
Cutting Attachment Inspection
Look for signs of damage to the cutting
attachment (see pages 33 and 39). Replace
any cutting attachment and parts that are worn
out, bent, cracked, chipped, or damaged in any
way.
If using a metal blade, be sure it is sharp. À
duil blade is more likely to snag and thrust.
If using a metal blade on a trimmer equipped
with a loop handle, be sure the barrier bar
(optional part) is installed beneath the loop
handle.
Make sure the cutting attachment is properly
installed and securely fastened (see pages 38
and 40).
Check that the debris shield is the correct
shield for the cutting attachment (see page 9),
and that it is securely installed and in good
condition.
Maintenance Inspection
e Check the oil level (see page 26). Running the
engine with a low oil level can cause engine
damage.
Check the air filter (see page 27). A dirty air
filter will restrict air flow to the carburetor,
reducing engine and trimmer performance.
Check throttle cable free play (see page 30).
The cable must be correctly adjusted and
operate smoothly for good throttle control.
Check the fuel level (see page 31). Starting
with a full tank will help to eliminate or reduce
operating interruptions for refueling.
15
BEFORE OPERATION
ARE YOUR SHOULDER HARNESS AND TRIMMER CORRECTLY ADJUSTED?
~ Adjusting the Harness Balancing the Trimmer on the Shoulder
Adjust the harness so the quick-release latch is Harness
at your right hip, as shown. Hang the trimmer on the harness hook, and see
В how it balances. ‘
Adjust the shoulder harness, the hanger clamp on
the trimmer shaft, and the loop handle or U-type
handlebar, so the handle or handlebars are in a
comfortable operating position, and the trimmer
hangs with its cutting attachment a few inches
above the ground (see page 19).
QUICK-RELEASE
LATCH
FULL SHOULDER HARNESS
A few inches above
the ground
[ER +
GROUND T
QUICK-RELEASE
LATCH
SINGLE-STRAP SHOULDER HARNESS
16
OPERATION
SAFE OPERATING PRECAUTIONS
Before operating the trimmer for the first time, please review the IMPORTANT SAFETY INFORMA TION
on page 4 and the chapter titted BEFORE OPERATION.
Even if you have operated other trimmers, take time to become familiar with the operation of this
trimmer’s controls and handling.
For your safety, avoid starting or operating the engine in an enclosed area, such as a garage. Your
engine's exhaust contains poisonous carbon monoxide gas which can collect rapidly in an enclosed
area and cause illness or death.
If the trimmer starts to shake or vibrate, stop the engine immediately. After the cutting head has
completely stopped, inspect it to determine the cause of the vibration. Sudden vibration is a sign of a
hazardous problem, such as a loose or damaged cutting attachment. Do not operate the trimmer until
the problem is corrected.
Prolonged exposure to vibration may cause vibration syndrome (Raynaud’s disease). Symptoms include
loss of skin color in the hands and numbness or a painful tingling sensation in the fingers, hands, and
arms. Regular users of any power equipment may feel the numbness or pain spontaneously, at any time
— not just after using the equipment. If any of the symptoms occurs, see a physician immediately.
FUEL RETURN TUBE
(clear plastic tube)
CHOKE LEVER
STARTING THE ENGINE
1. To start a cold engine, move the choke lever to
the CLOSED position.
To restart a warm engine, leave the choke
lever in the OPEN position.
2. To start a cold engine, or after refueling an
engine that has run out of fuel, press the
priming bulb repeatedly until fuel can be seen
in the clear-plastic fuel-return tube.
To restart a warm engine, it is not necessary to
press the priming bulb.
~ IGNITION
3. Set the throttle trigger in the starting position, BUTTON
using the throttle set button. | THROTTLE THROTTLE
o TRIGGER
To set the throttle trigger for starting, press the a
operator presence lever by gripping the control
handle, pull the throttle trigger, then press and
hold the throttle set button while releasing the
throttle trigger.
4. Move the ignition switch button to the ON (1)
OPERATOR
position. PRESENCE
LEVER
17
OPERATION
5. Set the trimmer on the ground, resting on the
debris shield and the fuel tank guard. Do not
allow the cutting line or blade to contact any
obstruction.
Always rest the trimmer on the ground for
starting, rather than holding it in the operating
position. That prevents the end of the trimmer
from swinging into something as you start the
engine.
6. With your left hand, hold the drive shaft
housing just ahead of the engine. With your
right hand, pull the starter grip lightly until you
feel resistance, then pull briskly. Return the
starter grip gently.
7. If the choke lever was moved to the CLOSED
position to start the engine, gradually move it to
the OPEN position as the engine warms up.
Allow the engine to warm up for a few minutes
after a cold start. When the engine is warm
enough to idle well, pull and release the throttle
trigger to disengage the throttle set button.
8. With the engine idling, hook the trimmer to your
shoulder harness. Be careful to avoid contact
with the cutting line head or blade while
handling the trimmer with the engine running.
The cutting line head or blade should not rotate
with the engine idling. If there is rotation at idle,
adjust the idle speed correctly before using the
trimmer. For idle adjustment, consult your
servicing dealer.
18
OPERATION
IGNITION
STOPPING THE ENGINE THROTTLE SWITCH
1. Release the throttle lever. TRIGGER
2. Move the ignition switch button to the OFF (O)
position.
Wait for the cutting line head or blade to stop
before allowing the end of the trimmer to
contact anything.
AWARNING
The blade will continue to spin briefly after
the engine has stopped or the throttle
trigger is released.
A coasting blade can cause injury.
Maintain proper control of the trimmer until
the blade has completely stopped rotating.
TRIMMER/HARNESS QUICK DISCONNECTION
To quickly detach the trimmer from the harness,
pull the quick-release latch tab upward.
Insert the latch tongue in the slot of the quick-
release latch to reattach the trimmer to the
harness.
TRIMMER OPERATION
Operating Position
Hold the trimmer firmly with both hands, with your
fingers and thumbs encircling the handles as
shown. This will help you to keep the trimmer
under control at all times.
e Keep firm footing and balance.
e Do not overreach.
e Keep the cutting attachment below waist level.
e Keep all parts of your body away from the
rotating cutting attachment and hot surfaces.
OPERATION
Throttle Operation
- Pull the throttle trigger toward the grip to increase
engine speed and start cutting attachment
rotation.
The trimmer has the greatest cutting force at
maximum engine speed.
Release the throttle trigger to reduce engine
speed. At idle, the cutting attachment should
coast to a stop.
Using a Nylon Cutting-Line Head
As the ends of the line wear away, more line must
be released from the cutting-line head. Your
trimmer is factory-equipped with either a manual-
feed or semiautomatic (bump-feed) cutting-line
head, which have different procedures for
releasing line.
The debris shield is equipped with a cutoff knife,
which automatically removes any excess line that
is released.
Manual-Feed Cutting-Line Head
Line must be released with the cutting-line head
stopped.
1. Stop the engine, and wait for the cutting-line
head to coast to a complete stop.
2. Hold the drum, pull the spool out about a
quarter of an inch, then turn the spool
counterclockwise until it snaps into the drum
again.
The spool will snap into the drum every sixth of
a turn, which releases 1 to 1-1/2 inches of line.
Semiautomatic (bump-feed) Cutting-Line Head
Line must be released with the cutting-line head
spinning rapidly.
With the engine running at full speed, tap the
cutting-line head on hard, bare ground.
Each tap releases about 2 inches of line.
20
THROTTLE
TRIGGER
IDLE
(cutting
attachment
stops)
FAST
(cutting”=
attachment
rotates)
'MANUAL-FEED CUTTING-LINE HEAD
To release more line,
pull spool and turn
A counterclockwise.
SEMIAUTOMATIC (bump-feed) CUTTING-LINE HEAD
OPERATION
Using Blades
Refer to the chart on page 9 for appropriate blade
applications.
If using a metal blade on a Honda trimmer
equipped with a loop handle, also install the
Honda conversion kit that includes a full shoulder
harness, a barrier bar, and a debris shield for
metal blades. Follow the installation instructions
and safety information that come with the kit.
Metal blades are supplied with a cover
surrounding the edge of the blade. For your
safety, and to protect the blade, the cover should
be installed whenever the trimmer is not in use.
Be sure to remove the blade cover before starting
the engine. Otherwise, the blade cover may fly off
at high speed.
If the trimmer starts to vibrate after the blade
strikes an object, stop the engine immediately and
check the blade for damage. A damaged blade
may break, and pieces of a broken blade can
become dangerous projectiles. Replace the blade
if it is broken, cracked, bent, or damaged in any
way.
SAFE OPERATING PRACTICES
Be very careful when operating the trimmer over
uneven or rough ground, and when the ground is
wet and slippery. Watch out for hidden obstacles
that could cause you to stumble. Operate the
trimmer only under conditions with good visibility.
Do not operate the trimmer where you cannot see
what it is cutting.
A WARNING
Rotating cutting lines can cause serious
abrasions and cuts, and blades can cut
deeply.
e Keep away from the cutting lines or blade
whenever the engine is running.
e Always stop the engine, and be sure the
cutting line head or blade has stopped
turning, before inspecting or handling the
cutting lines or blade.
Thrown Debris
The trimmer will throw debris in the direction of
blade movement at the point of contact.
The cutting line head or blade on Honda UMK422
and UMK431 trimmers rotates counterclockwise,
as viewed from the operator's position, so tilting
the cutting line head to the right will throw debris
away from you, and tilting to the left will throw
debris toward you.
DEBRIS
vu
uyy
hl!
(0 я]
O Cut with the right
side to throw debris
away from you.
If the cutting line head or blade is held parallel to
the ground, debris will scatter in all directions, and
there will be greater friction which will wear out
the cutting line or blade sooner.
When operating the trimmer near a hard surface,
such as a wall, work from an angle where debris
that strikes the hard surface will ricochet away
from you.
Gravel, loose stones, etc. can be picked up by the
nylon cutting lines or blade and thrown many feet
with enough force to cause serious personal
injury and/or property damage. Before crossing
graveled areas, release the throttle trigger to stop
the cutting line head or blade.
21
OPERATION
Blade Thrust (Kickback)
Blade thrust (kickback) is the sudden, forceful, O)
and uncontrolled movement of a blade-equipped EZ
trimmer that may occur if the blade binds in the Г
cut or strikes a solid object. BLADE 7»
THRUST rn e)
Blade thrust (kickback) throws the trimmer in the Ya N IS
direction opposite blade rotation at the point of N) г
contact, and the jolt received by the operator can К
result in further loss of control.
% >
To reduce the risk of loss of control, use metal “а, \ | 1 КМ
blades on trimmers equipped with a U-type = Ml AS” ASH
handlebar, or install the barrier bar (optional part) AY ANY ZW
on trimmers equipped with a loop handle.
Replace or resharpen dull blades. Dull blades are more likely to bind in the cut and cause blade thrust.
Watch out for hidden obstacles, such as rocks, stumps, roots, etc., that could cause the blade to kick
back if struck. Blade thrust is more likely to occur in areas where it is difficult to see what is being cut.
Understand the reaction forces of the blade. When using a brush blade to saw through heavy brush and
small saplings, saw with the side of the brush blade that is moving toward you and tends to pull the
trimmer away from you.
Blades on Honda UMK422 and UMK431 trimmers rotate counterclockwise, as viewed from the
operator's position. Therefore, the left side of the blade is moving toward you. With these trimmers,
sawing with the left side of a brush blade will give you better control and less risk of kickback, though it
will throw the sawdust toward you.
Cut from the side of saplings that will cause them to fall away from the trimmer. This will help to prevent
the blade from binding in the cut and kicking back.
Accelerate the engine to maximum speed before starting the cut, and saw through with uniform
pressure.
OPERATING TIPS
Scything
Swing the trimmer in a level arc by rotating your SCYTHING
body with a smooth, easy motion, rather than
moving the trimmer with your arms. Do not chop
at tough weeds and brush; let the cutting line or
blade work through tough growths gradually. | |
To direct thrown debris away from you, tilt the |
cutting attachment to the right side, scythe from
left to right, then return without cutting. NTE |
22
OPERATION
Trimming and Edging
Use nylon line for cutting against a hard surface.
Work from an angle where debris that strikes the
hard surface will ricochet away from you.
Avoid contact with wires, wire fences, metal rods,
etc. Overlapping a wire will cause the nylon line to
wrap around the wire and break off.
Brush Clearing
Clearing brush with a brush blade may require
both scything and sawing.
Scything with the right side of the blade will direct
thrown debris away from you.
Be especially careful to direct debris away from
you if recutting an area to shorten stumps. Short
lengths of shrub and sapling stumps may tear off
and be thrown at high speed.
Sawing heavy brush and saplings with the left
side of the blade will reduce the risk of kickback.
Accelerate the engine to maximum speed before
starting the cut, and saw through with uniform
pressure.
If shrubs or saplings bind the blade, stop the
engine, and while supporting the weight of the
trimmer, push the shrub or sapling away to free
the blade. Do not use the blade as a lever.
Operation on Slopes
TRIMMING
al An
SAWING
Start on the low side of a slope, and work upward. This will reduce your risk of slipping and falling, and it
will give you a cutting angle that will better enable you to direct debris away from you.
Do not let the cutting line or blade dig into the slope, because that can cause stones and dirt to be
thrown at you.
Do not raise the cutting attachment above waist level during operation, because that would increase the.
risk of thrown objects striking your face.
Avoid steep slopes that would require holding the cutting attachment above waist level. Avoid slippery
slopes that might cause you to lose your balance.
23
SERVICING YOUR HONDA TRIMMER
THE IMPORTANCE OF MAINTENANCE
Good maintenance is essential for safe,
economical, and trouble-free operation. It will also
help reduce air pollution.
AWARNING
improperly maintaining this trimmer, or
failure to correct a problem before
operation, can cause a malfunction in
which you can be seriously hurt or killed.
Always follow the inspection and
maintenance recommendations and
schedules in this owner’s manual.
To help you properly care for your trimmer, the
following pages include a maintenance schedule,
routine inspection procedures, and simple
maintenance procedures using basic hand tools.
Other service tasks that are more difficult, or
require special tools, are best handled by
professionals and are normally performed by a
Honda technician or other qualified mechanic.
The maintenance schedule applies to normal
operating conditions. If you operate your trimmer
under severe conditions, such as sustained high-
load or high-temperature operation, or use it in
unusually wet or dusty conditions, consult your
servicing dealer for recommendations applicable
to your individual needs and use.
Remember that your servicing dealer knows your
trimmer best and is fully equipped to maintain and
repair it.
To ensure the best quality and reliability, use only
new, genuine Honda parts or their equivalents for
repair and replacement.
Maintenance, replacement, or repair of the
emission control devices and systems may be
performed by any engine repair establishment
or individual, using parts that are “certified” to
EPA standards.
24
MAINTENANCE SAFETY
Some of the most important safety precautions
follow. However, we cannot warn you of every
conceivable hazard that can arise in performing
maintenance. Only you can decide whether or not
you should perform a given task.
[| AWARNING
Failure to properly follow maintenance
instructions and precautions can cause
you to be seriously hurt or killed.
Always follow the procedures and
precautions in the owner's manual.
Safety Precautions
e Make sure the engine is off before you begin
- any maintenance or repairs. This will eliminate
several potential hazards:
— Carbon monoxide poisoning from
‘engine exhaust. Be sure there is adequate
ventilation whenever you operate the
engine.
— Burns from hot parts.
Let the engine and exhaust system cool
before touching.
— Injury from moving parts.
Do not run the engine unless instructed to
do so.
Read the instructions before you begin, and
make sure you have the tools and skills
required.
e To reduce the possibility of fire or explosion,
“be careful when working around gasoline. Use
only a nonflammable solvent, not gasoline, to
clean parts. Keep cigarettes, sparks, and
flames away from all fuel-related parts.
SERVICING YOUR HONDA TRIMMER
MAINTENANCE SCHEDULE
REGULAR SERVICE PERIOD (3) | Before | First | Every 31 Every 8 Every | Every 2 | Referto |
TEM Format sven dos monk eN dee —| Sh | asu | ooh 100 His. | 0 His. | number |
e | Engine oil | “Check| O | | 26 |
a — Change o o | | 26
e | Air filter — Check| O do _ 27
Clean O(1)| 27
Throttle cable ) Check | O ВЕ ! | 30
Cutting attachment Check | O a a 133&39
Debris shield > Check| O 33839
Nuts, bolts, fasteners Check- | 5
Retighten if | O —
— necessary
Engine cooling fins Check | © 30
Shoulder harness quick-release Check | O | 19
° Idle speed adjust O(2) —
e | Valve clearance Check-
a Adjust | — 90@)| —
Gear case a Lubricate | O(2) —
Clutch shoes and drum Check O(2) —
e | Spark plug Check- o 8
Clean
Replace I o 28
Spark arrester Clean O | | 29
* | Fuel filter Check _ O | 32
* | Fuel tank Clean | o 32
* | Fuel tubes Check Every two years [replace (2) if necessary] | 32
e Emission-related items
(1) Service more frequently when used in dusty areas.
(2) These items should be serviced by your servicing dealer, unless you have the proper tools and are
mechanically proficient. Refer to the Honda shop manual for service procedures.
(3) Log hours of operation to determine proper maintenance intervals.
25
SERVICING YOUR HONDA TRIMMER
ENGINE
Engine Oil Level Check
Check the engine oil level before each use, or
every 10 hours if operated continuously. Rest the
trimmer on a level surface, with the engine
stopped and in an upright position.
FILLER OPENING
1. Remove the filler cap/dipstick and wipe it
— clean.
2. Insert and remove the dipstick without
screwing it into the filler opening. Check the oil
level shown on the dipstick. FILLER CAP/DIPSTICK
3. If the oil level is low, fill to the edge of the oil
filler hole with the recommended oil (see page
27). To avoid overfilling or underfilling, be sure
the engine is in a level position, as shown.
Running the engine with too little or too much
oil can cause engine damage.
OIL LEVEL
4. Screw in the filler cap/dipstick securely.
Engine Oil Change
Drain the used oil while the engine is warm.
Warm oil drains quickly and completely.
1. Place a suitable container below the engine to
catch the used oil, then remove the filler cap/
dipstick and drain the used oil through the filler FILLER OPENING
opening. Allow the used oil to drain completely.
Improper disposal of engine oil can be harmful
to the environment. If you change your own oil,
please dispose of the used oil properly. Put it in
a sealed container, and take it to a recycling
center. Do not discard it in a trash bin or dump
it on the ground. | |
3. With the engine in an upright position, fill to the
edge of the ail filler hole with the recommended
oil (see page 27).
Engine oil capacity: 0.11 US qt (3.38 fl. oz,
0.1 2)
4. Screw in the filler cap/dipstick securely.
26
SERVICING YOUR HONDA TRIMMER
Engine Oil Recommendations
Oil is a major factor affecting performance and service life. Use 4-stroke automotive detergent oil.
SAE 10W-30 is recommended for all temperatures within the recommended operating range for these
trimmers. The recommended operating range extends from 23°F (-5°C) to 104°F (40°C).
The SAE oil viscosity and service classification are in the API label on the oil container. Honda
recommends that you use API SERVICE category SF or SG oil.
Air Filter Inspection
Press the air cleaner latch tab, and remove the air cleaner cover. Check the filter to be sure it is clean
and in good condition.
If the filter is dirty, clean it as described under Air Filter Cleaning. Replace the filter if it is damaged.
Reinstall the filter and air cleaner cover.
Operating the engine without an air filter, or with a damaged air filter, will allow dirt to enter the engine,
causing rapid engine wear. This type of damage is not covered by the Distributors Limited Warranty.
Air Filter Cleaning
A dirty air filter will restrict air flow to the —
carburetor, reducing engine performance. If you
operate the engine in very dusty areas, clean the FILTER
air filter more often than specified in the AIR
MAINTENANCE SCHEDULE. CLEANER
COVER
1. Clean the air filter in warm soapy water, rinse,
and allow to dry thoroughly. Or clean in
nonflammable solvent and allow to dry.
2. Dip the air filter in clean engine oil, then
squeeze out all excess oil. The engine will
smoke when started if too much oil is left in the
filter.
3. Wipe dirt from the air cleaner base and cover,
using a moist rag. Be careful to prevent dirt
from entering the carburetor. RETAINING TABS
27
SERVICING YOUR HONDA TRIMMER
Spark Plug Service
Recommended Spark plugs:
CR5HSB (NGK)
U16FSR-UB (DENSO)
Incorrect spark plugs can cause engine damage.
SPARK PLUG
1. Disconnect the spark plug cap, and remove
any dirt from around the spark plug area.
2. Remove the spark plug with a 5/8-inch spark
plug wrench.
3. Inspect the spark plug. Replace it if the
electrodes are worn, or if the insulator is
cracked or chipped. Clean the spark plug with
a wire brush if you are going to reuse it.
4. Measure the spark plug electrode gap with a SPARK PLUG CAP
suitable gauge. The gap should be
0.024 — 0.028 in (0.60 — 0.70 mm). Correct the
gap, if necessary, by carefully bending the side
electrode.
SIDE ELECTRODE
5. Install the spark plug carefully, by hand, to
avoid cross-threading.
6. After the spark plug seats, tighten with a 5/8- (0.60 — 070 m a Бен
inch spark plug wrench to compress the
washer.
If reinstalling the used spark plug, tighten
1/8 — 1/4 turn after the spark plug seats.
If installing a new spark plug, tighten 1/2 turn
after the spark plug seats.
A loose spark plug can overheat and damage
the engine. Overtightening the spark plug can
damage the threads in the cylinder head.
7. Attach the spark plug cap.
28
SERVICING YOUR HONDA TRIMMER
Spark Arrester Service
The spark arrester must be serviced every 100
hours to keep it functioning as designed.
If the engine has been running, the muffler will be
very hot. Allow the muffler to cool before servicing
the spark arrester. o
1. Remove the four 5 x 18 mm bolts from the
recoil starter, and remove the recoil starter.
2. Disconnect the spark plug cap from the spark
plug. Pull the spark plug wire and the ignition
switch wire out of the retainers in the top cover.
3. Remove the two 5 x 22 mm bolts from the top
cover, and remove the top cover.
4. Remove the three 5 mm screws from the
muffler cover, and remove the muffler cover.
5. Remove the 4 mm screw from the spark
arrester, and remove the spark arrester.
6. Use a brush to remove carbon deposits from
the spark arrester screen. Be careful to avoid
damaging the screen.
The spark arrester must be free of breaks and
holes. Replace the spark arrester if it is
damaged.
7. Install the spark arrester, muffler cover, top
cover, and recoil starter in the reverse order of
disassembly.
SPARK
ARRESTER
SCREEN
SPARK
ARRESTER
4 mm SCREW
RECOIL
x 18 mm BOLTS
RETAINERS. a
N — | SPARK
> YO PLUG
RÉ E CT a, | CAP
Ñ As N SPARK
AZ
IGNITION
SWITCH
5x22 mm
BOLTS
— 5 x 16 mm SCREW
MUFFLER
COVER
5 x 10 mm SCREW
5x10 mm SCREW
29
SERVICING YOUR HONDA TRIMMER
Cooling Fin Inspection
Inspect the engine cooling fins, and clean out dirt
and debris if they are clogged.
If it is necessary to remove the top cover for
better access to the cooling fins, follow
disassembly steps 1 through 3 on page 29.
Throttle Cable Inspection
Verify that the throttle trigger operates smoothly,
and the throttle cable is undamaged. If there is
visible damage, or if the throttle trigger does not
operate smoothly, have your Honda servicing
dealer replace the throttle cable.
Check the free play at the end of the throttle
cable. Free play should be 0 — 1/16 in (0 — 2 mm).
If adjustment is needed, use the following cable
adjustment procedure.
Throttle Cable Adjustment ADJUSTER
1. Loosen the lock nuts with a 10 mm wrench,
and move the adjuster in or out as required.
2. Tighten the lock nuts and recheck cable free
play.
30
ENGINE COOLING FINS
/ CABLE END FREE PLAY:
0-1/16 in (0 — 2 mm)
f
LOCK NUTS
SERVICING YOUR HONDA TRIMMER
FUEL SYSTEM
Refueling
Fuel tank capacities a
UMK422: 0.48 US qt/15.2 fl. oz (0.45 £)
UMK431: 0.69 US qt22.0 fl. oz (0.65 £)
FUEL TANK CAP
Check the fuel level by looking through the
translucent fuel tank. | |
If the fuel level is low, refuel in a well-ventilated
area with the engine stopped. If the engine has
‚been running, allow it to cool first.
To refuel, rest the trimmer on the ground with the
fuel tank cap facing up, as shown. Remove the
fuel tank cap, and fill the tank with gasoline to the
bottom of the filler neck. Refuel carefully to avoid
spilling fuel. Do not overfill. There should be no
fuel in the filler neck. After refueling, tighten the
fuel tank cap securely. — Fuel Recommendations
Use unleaded gasoline with a pump octane
AWARNING rating of 86 or higher.
Gasoline is highly flammable and These engines are certified to operate on
explosive. unleaded gasoline. Unleaded gasoline produces
fewer engine and spark plug deposits and
You can be burned or seriously injured extends exhaust system life.
when handling fuel.
Never use stale or contaminated gasoline or an
Stop the engine and keep heat, sparks, oil/gasoline mixture. Avoid getting dirt or water in
‘and flame away. the fuel tank.
e Handle fuel only outdoors.
« Wipe up spills immediately. Occasionally you may hear a light “spark knock
or “pinging” (metallic rapping noise) while
operating under heavy loads. This is no cause for
Never refuel the engine inside a building where concern.
gasoline fumes may reach flames or sparks. Keep Co
gasoline away from appliance pilot lights, If spark knock or pinging occurs at a steady
barbecues, electric appliances, power tools, etc. engine speed, under normal load, change brands
of gasoline. If spark knock or pinging persists, see
Spilled fuel is not only a fire hazard, it causes an authorized Honda servicing dealer.
environmental damage. Wipe up spills
immediately. NOTICE |
Move at least 10 feet (3 meters) away from the Running the engine with persistent spark knock or
fueling source and site before starting the engine. ~~ PINGING can cause engine damage.
Running the engine with persistent spark knock or
pinging is misuse, and the Distributor’s Limited
Warranty does not cover parts damaged by
misuse.
31
SERVICING YOUR HONDA TRIMMER
Fuel Tube Inspection
Check the fuel supply and return tubes, and
replace any tube that is damaged, cracked, or
leaking.
Refer to the Honda shop manual for tube
replacement instructions, or take the trimmer to a
Honda trimmer servicing dealer.
Fuel Filter and Fuel Tank Cleaning
1. Remove the fuel tank cap, and empty the fuel
tank into an approved gasoline container. Use
a funnel to avoid spilling gasoline.
2. Pull the fuel filter out through the fuel filler neck
by hooking the black fuel supply tube with a
piece of wire, such as a partly straightened
paper clip.
3. Inspect the fuel filter. If the fuel filter is dirty,
wash it with nonflammable solvent. Be careful
to avoid damaging the filter.
Replace the filter if it is damaged or
excessively dirty.
4. Rinse sediment from the fuel tank with
nonflammable solvent.
5. Insert the fuel filter in the fuel tank, and install
the fuel tank cap.
FUEL SUPPLY TUBE
(black)
32
FUEL
SUPPLY
TUBE
(black)
SERVICING YOUR HONDA TRIMMER
CUTTING ATTACHMENTS
There are several cutting attachments for your
trimmer. Use the following section to inspect,
remove, service and install a standard (factory-
installed) cutting attachment.
Always turn the engine switch to the OFF
position, and disconnect the spark plug cap
before performing any inspection, adjustment or
maintenance on the trimmer.
Cutting-Line Heads
All Honda trimmers come with either a manual or
semiautomatic cutting head. Read this section to
learn how to inspect, instal! new line, and remove
and install a cutting head from the trimmer.
Inspection
Make sure the nylon line is only sticking out of the
metal eyelets on the head. If any of the line has
come off the spool, follow the “Installing
Replacement Nylon Line” instructions in this
section to disassemble the spool and replace the
line.
Examine the entire head area, including the
debris shield, and clear or clean it free from dirt,
debris, loose string, wire, or any other foreign
materials.
For the semiautomatic head, verify the spool
cover is locked in place (page 35). For the manual
feed head, make sure the three-sided knob is
correctly tightened (page 36). For both head
styles, check for any cracks in the plastic, and
replace any damaged parts.
Installing Replacement Nylon Line
First, determine which cutting-line head style is on
your trimmer. A manual-feed trimmer head has a
three-sided knob on the bottom of the head, while
the semiautomatic head has a spring-loaded
round button on the bottom of the head.
Use only the line size specified for the trimmer
head. For original, factory-installed Honda cutting-
line heads, use 0.095- or 0.105-inch-diameter
nylon line. Do not use any kind of metal, wire or
wire rope line on the trimmer. Use only genuine
Honda replacement nylon trimmer line or the
equivalent.
33
SERVICING YOUR HONDA TRIMMER
Manual-Feed Cutting-Line Head
1. Clean any mud, dirt, debris, etc. from the area
around the trimmer head; otherwise, it will
make it more difficult to service.
2. Remove the three-sided knob: it has a left-
hand thread, so turn it clockwise to remove.
Remove the tension spring.
3. Remove the trimmer head from the drive bolt.
4. Clean any debris, dirt, or loose string away
from the drive bolt and the gear case.
5. Separate the two halves (drum and spool) of
the trimmer head, then remove any remaining
nylon line from the spool.
6. Measure about 12 feet (3.7 meters) of new
line, then thread one end through the eyelet
on the spool. Pull the line until the two lengths
are equal.
7. Hold the spool in your hand by the manual-
feed grip. Wind both lines together around the
spool, turning the spool in the direction shown
by the arrow.
8. When winding, it is important not to allow the
two lines to cross over each other. Position a
finger between the lines as you turn the spool
to prevent the lines from becoming crossed.
34
THREE-SIDED KNOB
DRIVE BOLT
TENSION SPRING
SPOOL
==
SPOOL
E
NYLON LINE
EYELET
Rotate spoo
this direction
to wind line.
NYLON
LINE
SERVICING YOUR HONDA TRIMMER
10.
11.
12.
13.
When you have about 6 inches (150 mm) of
line remaining, press the lines into the two
notches on the bottom of the spool as shown.
This will hold the line on the spool for
reassembly.
Guide the ends of the lines through the metal
eyelets on the drum. Push the spool into the
drum, but be careful not to let any line get
trapped outside the edges of the spool.
Hold the drum and spool firmly, then pull each NYLON LINE
line until you hear it snap out of the notch. It is METAL EYELET
okay if one line is longer than the other. Once
each line has snapped out, press the spool all
the way into the drum.
If you're not sure the line snapped out of the
notch, carefully pull the spool away from the
drum and inspect the line.
Slide the drum/spool assembly back on to the
the drive bolt, then install the spring. Hand
tighten the three-sided knob as tight as you
can, then loosen the knob about 1-1/2 turns.
Otherwise, it will be difficult to operate the
manual feed function of the trimmer head.
METAL EYELET
35
SERVICING YOUR HONDA TRIMMER
Semiautomatic (Bump-Feed) Cutting-Line Head
1. Clean any mud, dirt, debris, etc., from the
area around the trimmer head; otherwise, it
will make it more difficult to service.
2. Locate the square-shaped “PUSH AND
TWIST” button on the side of the trimmer
head.
3. Hold the drum section of the trimmer head
firmly, then press the “PUSH AND TWIST”
button in slightly, then turn the spool cover
slightly to line up the triangle index marks.
The spool cover and the semiautomatic
button will come loose from the drum.
4. Remove the spool and spring from the drum.
Remove any remaining nylon line from the
spool.
5. Measure about 12 feet (3.7 meters) of new
line, then thread one end through the eyelet
on the spool. Pull the line until the two lengths
are equal.
6. Hold the spool in your hand with the spring
side facing away. Wind both lines together
around the spool, turning the spool in the
direction shown by the arrow.
7. When winding, it is important not to allow the
two lines to cross over each other. Position a
finger between the lines as you turn the spool
to prevent the lines from becoming crossed.
36
PUSH AND TWIST
BUTTON
SEMIAUTOMATIC
INDEX MARKS
SPOOL
Rotate spool
this direction
to wind line.
NYLON LINE
SERVICING YOUR HONDA TRIMMER
8.
10.
11.
12.
When you have about 6 inches (150 mm) of
line remaining, press the lines into the two
notches on the bottom of the spool. This will
hold the line on the spool for reassembly.
Guide the ends of the lines through the metal
eyelets on the drum. Push the spool into the
drum; be careful not to let any loose line get
trapped outside the edges of the spool. Hold
the spool inside the drum, then place the
semiautomatic button and spool cover on top
of the spool.
Hold the spool cover, semiautomatic button
and drum together firmly, then pull each line
until you hear it snap out of the notch. It is
okay if one line is longer than the other.
If you're not sure if either line snapped out of
the notch, carefully lift the spool cover away
from the upper section and inspect the line.
Locate the index triangle mark on the drum
and line it up with the other triangle mark on
the “PUSH AND TWIST” button on the spool
cover. Press the cover against the drum, then
slightly turn the cover counter-clockwise until
it clicks in place. lt is not necessary to press
the “PUSH AND TWIST” button during
reassembly.
NYLON
SPOOL LINE
NOTCHES
METAL EYELET
SPRING
METAL EYELET
37
- SERVICING YOUR HONDA TRIMMER
Removal & Installation
This section shows you how to remove (and
install) either style trimmer head from your
trimmer.
1.
Insert the tip of the 4 mm hexagon wrench
(supplied with your trimmer) fully into the hole
on the gear case.
. Turn the trimmer head until you feel the tool
drop into the hole in the internal locking ring.
Verify the trimmer head does not turn.
. All drive bolts use left-hand threads. Make sure
the tool remains in the hole, then grasp the
trimmer head and turn it clockwise (as viewed
from the bottom of the trimmer head) to
remove.
. Remove the remaining parts (spacer, cover
plate and lock ring) from the drive bolt. Note
the order and orientation of each part as you
remove them.
. Installation is the reverse of removal. Always
clean debris, dirt, loose string, etc. from the
trimmer head and drive bolt before installation.
Tighten the trimmer head securely.
38
TRIMMER
HEAD
GEAR CASE
DRIVE BOLT
4 mm HEXAGON WRENCH
SPACER
COVER PLATE
E=———3«-——— LOCK RING
TRIMMER HEAD
SERVICING YOUR HONDA TRIMMER
Blades
Blade Inspection
Always wear gloves when working around the
blade. Before each use, check the blade for wear
and damage, and check the tightness of the blade
nut. Examine the entire head area, including the
debris shield, and clear or clean it free from dirt,
debris, loose string, wire, or any other foreign
materials.
AWARNING
A worn, damaged or cracked blade can
break, and pieces of the damaged blade
can become dangerous projectiles.
A dull blade is more likely to snag and
thrust (kickback).
Inspect the blade regularly, and do not
operate the trimmer with a dull, worn, or
damaged blade.
NORMAL WORN
BENT CRACKED
A dull blade can be sharpened, but a blade that is
worn out, bent, cracked, chipped, or otherwise
damaged must be replaced.
When a blade needs sharpening or replacement,
take the trimmer to a Honda trimmer servicing
dealer. Or, if you have a torque wrench, you can
remove and install a blade yourself.
Blade Removal & Installation (UMK431UNBA
only)
For models other than the UMK431UNBA, a
special Blade Installation Kit must be installed
before a blade can be used. Refer to the
instructions provided with that kit for blades
installed on other (loop handle) models.
Always wear gloves when working around the
blade. Always install the blade cover on the
blade.
A torque wrench is required to install a blade; if
you do not have one, have a Honda trimmer
servicing dealer tighten the blade nut for you. If
the blade nut is tightened too much, the blade bolt
can break. If is not tightened enough, the blade
could come off. In either case, it would be
possible for the blade to fly off while you are
operating the trimmer.
BLADE SHARPENING: To avoid weakening the
blade, or causing imbalance or poor cutting, the
blade should be sharpened by trained staff at a
Honda trimmer servicing dealer.
BLADE REPLACEMENT: Your Honda trimmer
servicing dealer has cutting attachments that
have been designed and approved for your
trimmer and are covered by a warranty. Non-
Honda attachments are usually designed for
universal applications. Although aftermarket
attachments may fit on your trimmer, they many
not meet factory specifications and could make
your trimmer unsafe.
39
SERVICING YOUR HONDA TRIMMER
1. Install the protective plastic cover (that came
with the blade) on the blade.
2. Insert the tip of the 4 mm hexagon wrench
(supplied with your trimmer) fully into the hole
on the gear case.
3. Turn the blade until you feel the tool drop into
the hole in the internal locking ring. Verify the
blade does not turn. The drive bolt and blade
nut use left-handed threads. Make sure the
universal tool remains in the hole, then loosen
(turn clockwise) the self-locking nut. Pay
attention to the order and orientation of the
parts as they are removed.
4. Installation is the reverse of removal. Make sure
you install the blade with the cutting edges in
the direction of rotation. Torque the blade nut to
14 ft-lb (19 N-m, 14 kg-m).
Changing the Debris Shield
Refer to the applicable illustration for removing
and installing the debris shields. Note that the
cutting-line shield uses an additional spacer plate
and the longer 5 x 30 mm bolts.
Tighten the bolts securely. Torque the bolts to
2.5 ft-Ib (3.4 N:m, 0.34 kg-m).
SPACER
PLATES (2)
40
4 mm HEXAGON WRENCH
SPACER
DRIVE BOLT
COVER PLATE
LOCK RING — >= \
GLIDE CUP
SELF-LOCKING NUT
5x30 mm 5 x 20 mm
BOLTS (4) 5 BOLTS (4)
© oa 5 mm
WASHERS (4)
SPACER 5% SPACER
> PLATE
SPACER
PLATE
>
of 2
CUTTING-LINE
DEBRIS SHIELD
BRUSH/WOOD BLADE
DEBRIS SHIELD
STORAGE
STORAGE PREPARATION
Proper storage preparation is essential for
keeping your trimmer troublefree and looking
good. The following steps will help to keep rust
and corrosion from impairing your trimmer’s
function and appearance, and will make the
engine easier to start when you use the trimmer
again.
Cleaning
Wash the trimmer, including the area around the
trimmer head.
Wash the engine by hand, and be careful to
prevent water from entering the air cleaner.
Using a garden hose or pressure washing
equipment can force water into the air cleaner.
Water in the air cleaner will soak the filters and
can enter the carburetor or engine, causing
damage.
Water on a hot engine can cause damage. If the
engine has been running, allow it to cool for at
least 1/2 hour before washing.
If using a garden hose or pressure washing
equipment to clean the trimmer, be careful to
avoid getting water into controls and cable, or
anywhere near the engine air cleaner or muffler
opening.
Before washing the trimmer head area,
disconnect the spark plug cap.
After washing the trimmer, wipe dry all accessible
surfaces.
Start the engine outdoors, and let it run until it
reaches normal operating temperature to
evaporate any water remaining on the engine.
Stop the engine and allow it to cool.
After the trimmer is clean and dry, touch up any
damaged paint, and coat other areas that may
rust with a light film of oil. Lubricate the control
cable cores with a silicone spray lubricant.
Fuel
Gasoline will oxidize and deteriorate in storage.
Old gasoline will cause hard starting, and it leaves
gum deposits that clog the fuel system. If the
gasoline in your trimmer deteriorates during
storage, you may need to have the carburetor and
other fuel system components, serviced or
replaced.
The length of time that gasoline can be left in your
fuel tank and carburetor without causing
functional problems will vary with such factors as
gasoline blend, your storage temperatures, and
whether the fuel tank is partially or completely
filled. The air in a partially filled fuel tank promotes
fuel deterioration. Very warm storage
temperatures accelerate fuel deterioration. Fuel
deterioration problems may occur within a few
months, or even less if the gasoline was not fresh
when you filled the fuel tank.
The Distributors Limited Warranty does not cover
fuel system damage or engine performance
problems resuiting from neglected storage
preparation.
You can extend fuel storage life by adding a
gasoline stabilizer that is formulated for that
purpose, or you can avoid fuel deterioration
problems by draining the fuel tank and carburetor.
41
STORAGE
Adding Fuel Stabilizer to Extend Fuel Storage
Life
When adding a fuel stabilizer, fill the fuel tank with
fresh gasoline. If only partially filled, air in the tank
will promote fuel deterioration during storage. If
you keep a container of gasoline for refueling, be
sure that it contains only fresh gasoline.
Add fuel stabilizer following the manufacturer's
instructions.
After adding a fuel stabilizer, run the engine
outdoors for 10 minutes to be sure that treated
gasoline has replaced the untreated gasoline in
the carburetor.
Draining the Fuel Tank and Carburetor
Disconnect the spark plug cap. Make sure the
engine switch is in the STOP position.
Drain the fuel from the fuel tank to a suitable
container. Pull the starter grip a few times to draw
any remaining fuel out of the carburetor, then
drain this fuel from the tank.
Engine Oil
Change the engine oil (see page 26).
Carburetor & Air Cleaner
Clean the air filter (see page 27) and move the
choke lever to the CLOSED position.
Blade
If a blade is installed, put the blade cover on the
blade.
Engine Cylinder
Remove the spark plug (see page 28). Pour a 1/4
tablespoon (1 — 3 cc) of clean engine oil into the
cylinder. Pull the starter rope several times to
distribute the oil in the cylinder. Reinstall the
spark plug. Pull the starter rope slowly until
resistance is felt then return the starter grip
gently. This closes the valves so moisture cannot
enter.
42
STORAGE PRECAUTIONS
If your trimmer will be stored with gasoline in the
fuel tank and carburetor, it is important to reduce
the hazard of gasoline vapor ignition. Select a
well-ventilated storage area away from any
appliance that operates with a flame, such as a
furnace, water heater, or clothes dryer. Also avoid
any area with a spark-producing electric motor, or
where power tools are operated.
If possible, avoid storage areas with high
humidity, because that promotes rust and
corrosion.
With the engine and exhaust system cool, cover
the trimmer to keep out dust. A hot engine and
exhaust system can ignite or melt some materials.
Do not use sheet plastic as a dust cover. A non-
porous cover will trap moisture, promoting rust
and corrosion.
REMOVAL FROM STORAGE
Check your trimmer as described in the BEFORE
OPERATION chapter of this manual.
If the fuel was drained during storage preparation,
fill the tank with fresh gasoline. If you keep a
container of gasoline for refueling, be sure that it
contains only fresh gasoline. Gasoline oxidizes
and deteriorates over time, causing hard starting.
If the cylinder was coated with oil during storage
preparation, the engine will smoke briefly at
startup. This is normal.
TRANSPORTING
BEFORE LOADING
If the engine has been running, allow it to cool for
at least 15 minutes before loading the trimmer on
the transport vehicle. A hot engine and exhaust
system can burm you and can ignite some
materials.
Always turn the ignition switch to the OFF
position. Make sure the fuel cap is securely
tightened.
LOADING
The trimmer may be secured by suitable clamps,
hangers or straps. Secure the trimmer by at least
two points along the metal section of the drive
shaft tube. Avoid securing the trimmer by the
engine, cutting head/gearbox or handle area. The
trimmer should be secured in a horizontal
position, with the engine turned up.
Don’t hang the trimmer by the gearbox or cutting
head, or they may be damaged.
43
TAKING CARE OF UNEXPECTED PROBLEMS
STARTING PROBLEMS
Engine Will Not Start Possible Cause Correction
Check control positions. Ignition switch OFF. Turn ignition switch ON.
Choke not in CLOSED (cold Move choke to the CLOSED
engine). position.
Check fuel. Out of fuel. Add fuel.
Bad fuel, trimmer stored without
treating or draining gasoline,
refueled with bad gasoline.
Drain fuel tank and carburetor,
refuel with fresh gasoline.
Remove spark plug.
Spark plug faulty, fouled, or has
incorrect gap.
Clean, gap, or replace the spark
plug.
Take trimmer to an
authorized Honda
servicing dealer, or refer
to shop manual.
Fuel filter clogged, carburetor
malfunction, ignition malfunction,
valves stuck, etc.
Replace or repair faulty
components as needed.
ENGINE OPERATING PROBLEMS
Low Power or Engine
Speed Won't Increase
Possible Cause
Correction
Check air filter.
Filter dirty or clogged.
Check, clean or replace air filter.
Check fuel filter.
Filter dirty or clogged.
Replace fuel filter.
| Check throttle cable.
Out of adjustment, broken, or
bent.
Adjust cable, or replace if
necessary.
Check spark arrester.
Screen clogged.
Clean screen.
44
TAKING CARE OF UNEXPECTED PROBLEMS
CUTTING HEAD PROBLEMS
Blade or Cutting-line
head won't stop turning
when throttle is at
SLOW position
Possible Cause
Correction
Check throttle control and
cable.
Fault in throttle control or cable;
throttle cable out of adjustment or
bent.
Idle speed is too fast.
Check throttle control parts, adjust
or replace cable if necessary.
Adjust idle speed.
Check clutch. Clutch springs broken or worm, or | Replace clutch springs or replace or
clutch system faulty. repair other clutch system parts.
Blade or Cutting-Line Possible Cause Correction
Head Won't Turn
Check clutch, drive shaft,
and gearbox.
Worn or broken clutch, broken
shaft, worn or broken gearbox
parts.
Replace or repair faulty
components as needed.
Excessive Vibration
Possible Cause
Correction
Check Cutting-line head
or blade nut.
Cutting-Line head or blade nut
loose.
Tighten Cutting-line head or blade
nut securely.
Check blade.
Blade damaged.
Replace blade.
45
TECHNICAL & CONSUMER INFORMATION
TECHNICAL INFORMATION
This section contains important information about
serial number locations, operation at high
altitudes, oxygenated fuels and emissions control
systems.
Serial Number Locations
There are two serial numbers, one for the trimmer
and another for the engine. Record these number
in the space provided. You'll need to have these
numbers available when ordering parts or making
technical or warranty inquires (page 51).
ENGINE SERIAL
NUMBER
FRAME SERIAL NUMBER
46
Carburetor Modifications for High Altitude
Operation
At high altitude, the standard carburetor air-fuel
mixture will be too rich. Performance will
decrease, and fuel consumption will increase. A
very rich mixture will also foul the spark plug and
cause hard starting.
High altitude performance can be improved by
specific modifications to the carburetor. If you
always operate your trimmer at altitudes above
5,000 feet (1,500 meters), have your servicing
dealer perform this carburetor modification.
Even with carburetor modification, engine
horsepower will decrease about 3.5% for each
1,000-foot (300-meter) increase in altitude. The
effect of altitude on horsepower will be greater
than this if no carburetor modification is made.
When the carburetor has been modified for high
altitude operation, the air-fuel mixture will be too
lean for low altitude use.
Operation at altitudes below 5,000 feet (1,500
meters) with a modified carburetor may cause the
engine to overheat and result in serious engine
damage. For use at low altitudes, have your
servicing dealer return the carburetor to original
factory specifications.
TECHNICAL & CONSUMER INFORMATION
Oxygenated Fuels
Some conventional gasolines are being blended with alcohol or an ether compound. These gasolines
are collectively referred to as oxygenated fuels. To meet clean air standards, some areas of the USA
and Canada use oxygenated fuels to help reduce emissions. If you use an oxygenated fuel, be sure it is
unleaded and meets the minimum octane rating requirement. Before using an oxygenated fuel, try to
confirm the fuel's contents. Some states/provinces require this information to be posted on the pump.
The following are the EPA approved percentages of oxygenates:
ETHANOL —— (ethyl or grain alcohol) 10% by volume
You may use gasoline containing up to 10% ethanol by volume. Gasoline containing
ethanol may be marketed under the name “Gasohol”.
MTBE ———— (Methyl Tertiary Butyl Ether) 15% by volume
You may use gasoline containing up to 15% MTBE by volume
METHANOL — (methyl or wood alcohol) 5% by volume
You may use gasoline containing up to 5% methanol by volume, as long as it also
contains cosolvents and corrosion inhibitors to protect the fuel system. Gasoline
containing more than 5% methanol by volume may cause starting and/or performance
problems. It may also damage metal, rubber, and plastic parts of your fuel system.
If you notice any undesirable operating symptoms, try another service station, or switch to another
brand of gasoline. Fuel system damage or performance problems resulting from the use of an
oxygenated fuel containing more than the percentages of oxygenates mentioned above are not covered
under warranty.
47
TECHNICAL & CONSUMER INFORMATION
Emissions Control System Information
Source of Emissions
The combustion process produces carbon
monoxide, oxides of nitrogen, and hydrocarbons.
Control of hydrocarbons and oxides of nitrogen is
very important because, under certain conditions,
they react to form photochemical smog when
subjected to sunlight. Carbon monoxide does not
react in the same way, but it is toxic.
Honda utilizes lean carburetor settings and other
systems to reduce the emissions of carbon
monoxide, oxides of nitrogen, and hydrocarbons.
The U.S. and California Clean Air Acts
EPA and California regulations require all
manufacturers to furnish written instructions
describing the operation and maintenance of
emissions control systems.
The following instructions and procedures must
be followed in order to keep the emissions from
your Honda engine within the emissions
standards.
Tampering and Altering
Tampering with or altering the emissions control
system may increase emissions beyond the legal
limit. Among those acts that constitute tampering
are:
Removal or alteration of any part of the intake,
fuel, or exhaust systems.
Altering or defeating the speed-adjusting
mechanism to cause the engine to operate
outside its design parameters.
48
Problems that may Affect Emissions
If you are aware of any of the following
symptoms, have your engine inspected and
repaired by your servicing dealer.
Hard starting or stalling after starting.
Rough idle.
Misfiring or backfiring under load.
Afterburning (backfiring).
Black exhaust smoke or high fuel
consumption.
Replacement Parts
The emissions control systems on your new
Honda engine were designed, built, and certified
to conform with EPA and California emissions
regulations. We recommend the use of genuine
Honda parts whenever you have maintenance
done. These original-design replacement parts
are manufactured to the same standards as the
original parts, so you can be confident of their
performance. The use of replacement parts that
are not of the original design and quality may
impair the effectiveness of your emissions control
system.
A manufacturer of an aftermarket part assumes
the responsibility that the part will not adversely
affect emissions performance. The manufacturer
or rebuilder of the part must certify that use of the
part will not result in a failure of the engine to
comply with emissions regulations.
Maintenance
Follow the maintenance schedule on page 25.
Remember this schedules is based on the
assumption that your machine will be used for its
designed purpose. Sustained high-load or high-
temperature operation, or use in unusually wet or
dusty conditions, will require more frequent
service.
TECHNICAL & CONSUMER INFORMATION
Specifications
FEATURES
UMK422LNA | UMK422LTA | UMK431LNA | UMK431LTA | UMK431UNBA
GX22 1 hp e e
GX33 1.5 hp ©
Loop handle e e
U-type handle e
van a feed e optional e optional e
Semiautomatic optional e optional e optional
Saw blade optional; requires o
Blade installation Kit
DIMENSIONS
Handle UMK422 UMK431
installed
Length loop Manual feed head: 6.15 feet (1.875 m)
Semiautomatic feed head: 6.20 feet (1.89 m)
U-type' 6.27 feet (1.91 m)
Width loop 13.6 in (345 mm)
U-type — 23.8 in (605 mm)
Height loop 10.4 in (265 mm)
U-type' —— 16.3 in (415 mm)
Dry weight loop 13.9 Ib. (6.3 kg) 14.8 Ib. (6.7 kg)
U-type' — 16.1 Ib. (7.3 kg)
' with saw blade installed
49
TECHNICAL & CONSUMER INFORMATION
ENGINE
UMK422 UMK431
Model GX22 GX31
Engine type 4-stroke, overhead valve, single cylinder
Displacement 1.3 cu-in (22 cm?) 1.9 cu-in (31 cm*)
Bore& stroke 1.3 x 1.0 in (33 x 26 mm) 1.5 x 1.0 in (39 x 26 mm)
Max. output 1 hp (0.74 kW) at 7,000 rpm 1.5 hp (1.1 kW) at 7,000 rpm
Max. torque 0.8 ft-Ibs (1.09 Nem) at 4,500 rpm 1.23 ft-Ibs (1.64 Nem) at 4,500 rpm
Ignition system Transistorized magneto
Spark plugs NGK: CR5HSB, DENSO: U16FSR-UB
Starting system Recoil
Fuel Unleaded gasoline (86 octane or higher)
Fuel tank capacity
0.48 US qt/15.2 fl. oz (0.45 2) 0.69 US qt/22.0 fi. 0z (0.65 2)
Fuel consumption
0.55 Ib/hph (340 g/kWh, 250 g/psh)
Oil capacity 0.11 US qt/3.38 fl. oz (0.1 2)
Carburetor type Diaphragm type (overflow return) with fuel pump
Air cleaner single element, semi-dry
Idle speed 3,100 +200 rpm
FRAME
UMK422 UMK431
Engine switch Slide type
Throttle control
Two motion trigger style
Main pipe diameter
0.94 in (24 mm) 1.02 in (26 mm)
Main pipe thickness
0.07 in (1.7 mm) 0.08 in (2.0 mm)
Drive shaft solid 0.28 in. (7 mm)
Shaft support bushings 5 7
Gearbox ratio 1.31 1.33
Gearbox type Sealed ball bearings, helical cut gears, no shims required
Clutch engagement 4,400 rpm
Clutch type 2-1/8 inch, 7 spline 3-1/16 inch, 7 spline
50
TECHNICAL & CONSUMER INFORMATION
CONSUMER INFORMATION
Honda Publications
Two other documents are available from your Honda dealer. There is a Shop Manual, which covers
complete maintenance and overhaul procedures. It is intended to be used by a skilled technician. There
is also a Parts Catalog, that provides a complete, illustrated parts lists.
Warranty Service Information
Honda Power Equipment dealership personnel are trained professionals. They should be able to answer
any question you may have. If you encounter a problem that your dealer does not solve to your
satisfaction, please discuss it with the dealership's management. The Service Manager or General
Manager can help. Aimost all problems are solved in this way.
If you are dissatisfied with the decision made by the dealership's management, contact the Honda
Power Equipment Customer Relations Office. You can write:
American Honda Motor Co., Inc.
Power Equipment Division
Customer Service Office
4900 Marconi Drive
Alpharetta, GA 30005
Or telephone: (770) 497-6400
When you write or call, please give us this information:
Model and serial numbers (see page 46)
Name of the dealer who sold the trimmer to you
Name and address of the dealer who services your trimmer
Date of purchase
Your name, address, and telephone number
A detailed description of the problem
51
QUICK REFERENCE SECTION
UMK422 UMK431
Fuel Type Unleaded gasoline with pump octane rating of 86 or higher
(page 31)
Capacity 0.48 US qt/15.2 fl. oz (0.45 £) | 0.69 US qt/22.0 fl. oz (0.65 2)
Engine oil Type SAE 10W-30, API SF or SG (page 27)
Capacity 0.11 US qt/3.38 fl.oz (0.1 2)
Spark plug Type NGK: CR5HSB
DENSO: U16FSR-UB
Electrode gap 0.024 — 0.028 in (0.60 — 0.70 mm) |
Carburetor Idle speed 3,100 +200 rpm
Maintenance Before each use Check engine oil (page 26)
Check air filter (page 27)
Check throttle cable (page 30)
Check cutting attachment (pages 33 and 39)
Check debris shield (pages 33 and 39)
Check nuts, bolts, fasteners
First 10 hours
Check shoulder harness, quick release (page 19)
Change engine oil
Subsequent
Refer to the Maintenance Schedule on page 25.
OS POM52670-CVR
31VF9600 EM) 100.2003.04
Printed on
00X31-VF9-6000 Recycled Paper PRINTED IN U.S.A.