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.
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.
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.
TRIMMER SAFETY IMPORTANT SAFETY INFORMATION Honda UMK422 and UMK431 trimmerdbrush 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.
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.
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.
The shield’s cutoff knife automatically removes any excess line that is released from the cutting head. Honda UMK431 UNBA trimmers are supplied with two different debris shields. Use the debris shield with the cutoff knife when the cutting-line head is installed.
This type of debris shield does not have a cutoff knife. Honda UMK431 UNBA trimmers are supplied with a blade 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.
Brush/Wood Blade Cover Installation and Removal Place the blade cover on the blade halfway, starting with end A. To prevent the posts on end A from interfering with the debris shield, remove end A from the blade and place it beside the blade as shown.
COMPONENT & CONTROL LOCATIONS CUTTING-LINE HEAD GEAR CASE LOOP HANDLE DEBRIS SHIELD WITH CUTOFF KNIFE DRIVE SHAFT HOUSING IGNITION SWITCH UMK431 UNBA (supplied with two cutting attachments and debris shields) CUTTING-LINE HEAD FUEL TANK ARNESS HANGER THROlTLE BUlTON GEAR CASE...
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.
CONTROLS & 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...
Safety glasses or goggles that comply with standard 287.1 must be worn by the operator of any Honda trimmer/brush cutter. The safety glasses supplied with each new Honda UMK422 and UMK431 trimmedbrush comply with the ANSI standard. CONTROLS & EQUIPMENT FULL SHOULDER HARNESS...
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.
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.
BEFORE OPERATION ARE YOUR SHOULDER HARNESS AND TRIMMER CORRECTLY ADJUSTED? Adjusting Harness Shoulder Balancing Trimmer Adjust the harness so the quick-release latch is your right hip, shown. Hang FULL SHOULDER HARNESS QUICK. LATCH SINGLE-STRAP SHOULDER HARNESS Harness the trimmer on the harness hook, and see how it balances.
OPERATION SAFE OPERATING PRECAUTIONS Before operating the trimmer for the first time, please review the IMPORTANT SAFETY INFORMATlON on page 4 and the chapter titled BEFORE OPERATION. Even if you have operated other trimmers, take time to become familiar with the operation of this trimmer’s controls and handling.
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.
STOPPING THE ENGINE 1. Release the throttle lever. 2. Move the ignition switch button to the OFF (0) position. Wait for the cutting line head or blade to stop before allowing the end of the trimmer to contact anything. The blade will continue to spin briefly after the engine has stopped or the throttle trigger is released.
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.
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.
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.
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.
SERVICING YOUR HONDATRIMMER THE IMPORTANCE OF MAINTENANCE Good maintenance is essential for safe, economical, and trouble-free operation. It will also help reduce air pollution. 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.
SERVICING YOUR HONDA TRIMMER ENGINE Engine 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. 1. Remove the filler cap/dipstick and wipe it clean.
Engine Oil Recommendations Oil is a major factor affecting performance and service life. Use 4-stroke automotive detergent oil. SAE 1 OW-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.
SERVICING YOUR HONDATRIMMER Spark Plug Service Recommended Spark plugs: CRSHSB (NGK) U1 6FSR-UB (DENSO) NOTICE Incorrect spark plugs can cause engine damage. 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.
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. 1.
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 through 3 on page 29.
Refueling Fuel tank capacities UMK422: 0.48 US qt115.2 fl. oz (0.45 2) UMK431: 0.69 US qt122.0 fl. oz (0.65 2) 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.
SERVICING YOUR HONDATRIMMER 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. 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.
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.
SERVICING YOUR HONDA TRIMMER Manual-Feed Cutting-Line Head Clean any mud, dirt, debris, etc. from the area around the trimmer head; otherwise, it will make it more difficult to service. Remove the three-sided knob; it has a left- hand thread, so turn it clockwise to remove. Remove the tension spring.
9. 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. 10. Guide the ends of the lines through the metal eyelets on the drum.
SERVICING YOUR HONDA TRIMMER Semiautomatic (Bump-Feed) Cutting-Line Head Clean any mud, dirt, debris, etc., from the area around the trimmer head; otherwise, it will make it more difficult to service. Locate the square-shaped “PUSH AND TWIST” button on the side of the trimmer head.
8. 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. 9. Guide the ends of the lines through the metal eyelets on the drum.
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.
SERVICING YOUR HONDA TRIMMER Blade Removal & Installation (UMK431 UNBA only) For models other than the UMK431 UNBA, a special Barrier 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.
SERVICING YOUR HONDATRIMMER 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.
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.
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.
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 burn you and can ignite some materials. Always turn the ignition switch to the OFF position.
TAKING CARE OF UNEXPECTED PROBLEMS STARTING PROBLEMS Engine Will Not Start Check control positions. Check fuel. Remove spark plug. Take trimmer to an authorized Honda servicing dealer, or refer to shor, manual. ENGINE OPERATING PROBLEMS Low Power or Engine Speed Won’t Increase Check air filter.
CUTTING HEAD PROBLEMS Blade or Cutting-line Possible Cause head won’t stop turning when throttle is at SLOW Dosition Check throttle control and cable. throttle cable out of adjustment or bent. Idle speed is too fast. Check clutch. Clutch springs broken or worn, or clutch system faulty.
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 numbers in the space provided.
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 unleaded and meets the minimum octane rating requirement.
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.
Descriptive Term Moderate Intermediate Extended The Air index Information hang tag must remain on the trimmer/brush cutter until it is sold. Remove the hang tag before operating the trimmer/brush cutter. TECHNICAL & CONSUMER INFORMATION Applicable to Emissions Durability Period 50 hours (0-65 cc)
(1.875 m) Semiautomatic feed head: 6.18 feet (1.885 m) 13.6 in (345 mm) 10.4 in (265 mm) 13.9 Ib. (6.3 kg) UMK431 K1 6.27 feet (1.91 m) 23.8 in (605 mm) 16.3 in (41 15.0 Ib. (6.8 kg) 15.7 Ib. (7.1 kg)
0.028 in (0.60 0.70 mm) Intake: 0.1 0.02 mm Exhaust: 0.15 f 0.02 mm No other adjustments needed. UMK431 K1 1.02 in (26 mm) 0.08 in (2.0 mm) 1.33 6 inch, 7 spline MAINTENANCE Refer to page: 28 See your authorized...
TECHNICAL & CONSUMER INFORMATIQN 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.