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How to use this manual
A Few Words About Safety
How to use this manual
SERVICE INFORMATION
The service and repair information contained in this manual is intended for use by qualified, professional technicians. Attempting
service or repairs without the proper training, tools, and equipment could cause injury to you and/or others. It could also damage
this Honda product or create an unsafe condition.
This manual describes the proper methods and procedures for performing service, maintenance, and repairs. Some procedures
require the use special tools. Any person who intends to use a replacement part, service procedure or a tool that is not
recommended by Honda, must determine the risks to their personal safety and the safe operation of this product.
If you need to replace a part, use Honda Genuine parts with the correct part number or an equivalent part. We strongly recommend
that you do not use replacement parts of inferior quality.
For Your Customer's Safety
Proper service and maintenance are essential to the customer's safety and the reliability of this product. Any error or oversight
while servicing this product can result in faulty operation, damage to the product, or injury to others.
Improper service or repairs can create an un-
safe condition that can cause your customer or
others to be seriously hurt or killed.
Follow the procedures and precautions in this
manual and other service materials carefully.
For Your Safety
Because this manual is intended for the professional service technician, we do not provide warnings about many basic shop safety
practices (e.g., Hot parts-wear gloves). If you have not received shop safety training or do not feel confident about your knowledge
of safe servicing practice, we recommend that you do not attempt to perform the procedures described in this manual.
Some of the most important general service safety precautions are given below. However, we cannot warn you of every
conceivable hazard that can arise in performing service and repair procedures. Only you can decide whether or not you should
perform a given task.
Failure to properly follow instructions and pre-
cautions can cause you to be seriously hurt or
killed.
Follow the procedures and precautions in this
manual carefully.
Important Safety Precautions
Make sure you have a clear understanding of all basic shop safety practices and that you are wearing appropriate clothing and
using safety equipment. When performing any service task, be especially careful of the following:
• Read all of the instructions before you begin, and make sure you have the tools, the replacement or repair parts, and the skills
required to perform the tasks safely and completely.
• Protect your eyes by using proper safety glasses, goggles, or face shields anytime you hammer, drill, grind, or work around
pressurized air, pressurized liquids, springs or other stored-energy components. If there is any doubt, put on eye protection.
• Use other protective wear when necessary, for example gloves or safety shoes. Handling hot or sharp parts can cause severe
burns or cuts. Before you grab something that looks like it can hurt you, stop and put on gloves.
• Protect yourself and others whenever you have engine-power equipment up in the air. Anytime you lift this product with a hoist,
make sure that the hoist hook is securely attached to the product.
Make sure the engine is off before you begin any servicing procedures, unless the instruction tells you to do otherwise. This will
help eliminate several potential hazards:
• Carbon monoxide poisoning from engine exhaust. Be sure there is adequate ventilation whenever you run the engine.
• Burns from hot parts. Let the engine and exhaust system cool before working in those areas.
• Injury from moving parts. If the instruction tells you to run the engine, be sure your hands, fingers and clothing are out of the way.
Gasoline vapors and hydrogen gasses from battery are explosive. To reduce the possibility of a fire or explosion, be careful when
working around gasoline or batteries.
• Use only a nonflammable solvent, not gasoline, to clean parts.
• Never store gasoline in an open container.
• Keep all cigarettes, sparks, and flames away from the battery and all fuel-related parts.
gx240ut2_gx270ut2_gx340ut2_gx390ut2

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Summarization of Contents

Introduction
Safety Messages
Provides safety information and defines signal words like DANGER, WARNING, and CAUTION for safe servicing.
How to Use This Manual
Service Rules
Guidelines for using genuine parts, special tools, and proper procedures for maintenance and repair.
Symbols
Explains symbols used in the manual to denote specific service procedures and their meanings.
Abbreviations
Lists common abbreviations used in the manual for parts and systems.
Specifications
Serial Number Location
Identifies the location on the engine where the serial number, type code, and description code are stamped.
Type Code
Details various engine model type codes and their corresponding P.T.O. variations.
Dimensions and Weights
Provides dimensional and weight specifications for different engine models and P.T.O. variations.
Engine Specifications
Lists key engine specifications such as displacement, bore, stroke, and power output.
Performance Curves
Presents graphical data for engine torque and power output versus engine speed.
Dimensional Drawings
Illustrates the physical dimensions of engine models, with and without reduction units.
P.T.O. Dimensional Drawings
Provides detailed drawings of Power Take-Off (P.T.O.) dimensions for various types.
Service Information
Maintenance Standards
Details standard measurements and service limits for engine parts like pistons, rings, and valves.
Torque Values
Lists specified torque values for engine bolts and nuts to ensure proper assembly.
Lubrication & Seal Points
Identifies lubrication and seal points for various engine components.
Tools
Lists special and commercially available tools required for service procedures.
Harness Routing
Illustrates the routing of engine wire harnesses and connectors for different switch types.
Maintenance
Maintenance Schedule
Outlines recommended maintenance intervals based on time or operating hours.
Engine Oil Level Check
Procedure for checking the engine oil level using the oil filler cap and gauge.
Engine Oil Change
Step-by-step instructions for draining and refilling the engine oil.
Reduction Case Oil (1/2 reduction unit with clutch)
Details on checking and changing the oil in the reduction case.
Air Cleaner Check/Cleaning/Replacement
Procedures for inspecting, cleaning, and replacing air cleaner elements for different types.
Sediment Cup Cleaning
Instructions for cleaning the fuel sediment cup to ensure proper fuel flow.
Spark Plug Check/Adjustment
Guidance on inspecting and adjusting the spark plug gap for optimal performance.
Spark Plug Replacement
Steps for removing and installing a new spark plug, including torque specifications.
Spark Arrester Cleaning (if equipped)
Procedure for cleaning the spark arrester to prevent clogging and maintain performance.
Idle Speed Check/Adjustment
How to check and adjust the engine idle speed for stable operation.
Valve Clearance Check/Adjustment
Procedure for measuring and adjusting valve clearance for proper engine timing.
Combustion Chamber Cleaning
Instructions for cleaning carbon deposits from the combustion chamber.
Fuel Tank and Filter Cleaning
Steps for cleaning the fuel tank and filter to prevent fuel system issues.
Fuel Tube Check
Guidance on inspecting the fuel tube for signs of deterioration, cracks, or leakage.
Troubleshooting
Before Troubleshooting
Preliminary checks and precautions before starting troubleshooting procedures.
Troubleshooting: Hard Starting
Diagnostic steps for addressing an engine that is difficult to start.
Troubleshooting: Compression Issues
Diagnosing and resolving issues related to high or low cylinder compression.
Troubleshooting: Engine Speed Issues
Steps for diagnosing problems when engine speed does not increase or stabilize.
Troubleshooting: Engine Not Stopping
Diagnosing why the engine fails to stop when the combination/engine stop switch is turned off.
Troubleshooting: Engine Not Stopping Due to Low Oil
Diagnosing why the engine does not stop when the engine oil level is low.
Cover
Fan Cover Removal/Installation
Procedure for removing and installing the engine fan cover assembly.
Fuel System
Tools
Lists specialized tools required for fuel system service.
Fuel Tank Removal/Installation
Detailed steps for removing and installing the fuel tank and its components.
Air Cleaner Removal/Installation
Procedures for removing and installing air cleaner assemblies for various types.
Carburetor Removal/Installation
Instructions for removing and installing the carburetor assembly.
Carburetor Disassembly/Assembly
Detailed steps for disassembling and reassembling the carburetor.
Choke Diaphragm Disassembly/Assembly
Procedure for disassembling and reassembling the choke diaphragm assembly.
Carburetor Body Cleaning
Guidelines for cleaning carburetor passages and ports safely and effectively.
Carburetor Inspection
Methods for inspecting carburetor components like float level and valve.
Choke Diaphragm Inspection
How to inspect the choke diaphragm for smooth operation and proper vacuum seal.
Pilot Screw Replacement
Procedure for replacing the pilot screw, including specifications for various carburetor models.
Choke Set Replacement
Steps for replacing the choke valve plate and shaft.
Cylinder Stud Bolt Replacement
Instructions for replacing cylinder stud bolts, including specifications for different lengths.
Governor System
Governor Arm/Control Base Assy. Removal/Installation
Procedure for removing and installing the governor arm and control base assembly.
Auto Throttle (If Equipped) Removal/Installation
Steps for removing and installing the auto throttle system components.
Control Base Assy. Disassembly/Assembly
Detailed instructions for disassembling and reassembling the control base assembly.
Maximum Speed Adjustment
Procedure for adjusting the engine's maximum speed.
Solenoid (Auto Throttle) Inspection
Method for inspecting the auto throttle solenoid for proper operation.
Charging System
Tools
Lists specialized tools required for charging system service.
System Diagram
Illustrates the electrical connections for charging systems with different coil types.
Before Troubleshooting
Preliminary checks and precautions before diagnosing charging system issues.
Charging System Troubleshooting
Diagnostic flowcharts for troubleshooting common charging system problems.
Charge / Power Coil Removal/Installation
Procedure for removing and installing charging and power coils.
Charge/Power Coil Inspection
Methods for inspecting charge and power coils for resistance and continuity.
Ignition System
System Diagram
Provides a schematic of the ignition system's electrical connections.
Ignition System Troubleshooting
Diagnostic steps for identifying and resolving ignition system faults.
Ignition Coil Removal/Installation
Procedure for removing and installing the ignition coil assembly.
Ignition Coil Installation
Detailed steps for installing the ignition coil, including air gap adjustment.
Spark Test
Procedure for testing the spark plug's output to diagnose ignition issues.
Spark Plug Cap Inspection
How to check the spark plug cap for continuity.
Ignition Coil Inspection
Methods for inspecting ignition coil resistance between terminals.
Starting System
System Diagram
Illustrates the electrical schematic for the starting system.
Starting System Troubleshooting
Diagnostic steps for troubleshooting issues where the starter motor does not operate.
Recoil Starter Removal/Installation
Procedure for removing and installing the recoil starter assembly.
Recoil Starter Disassembly
Detailed steps for disassembling the recoil starter.
Recoil Starter Assembly
Instructions for assembling the recoil starter components.
Recoil Starter Inspection
Methods for inspecting recoil starter operation and components like the starter pulley.
Starter Motor Removal/Installation
Procedure for removing and installing the starter motor.
Starter Motor Disassembly/Assembly
Detailed steps for disassembling and reassembling the starter motor.
Inspection: Starter Motor Performance Test
Procedure for testing starter motor performance under load and no-load conditions.
Brush Replacement
Instructions for replacing worn starter motor brushes.
Other Electrical
Component Location
Identifies the location of key electrical components on the engine.
Control Box Removal/Installation
Procedure for removing and installing the engine's control box.
Control Box Disassembly/Assembly
Detailed steps for disassembling and reassembling the control box.
Oil Level Switch Inspection
How to inspect the oil level switch for continuity under different oil conditions.
Engine Stop Switch Inspection
Procedure for inspecting the engine stop switch continuity in various positions.
Combination Switch Inspection
How to inspect the combination switch continuity at each position.
Silicon Rectifier Inspection
Method for inspecting the silicon rectifier for continuity in one direction only.
Circuit Protector Inspection
How to inspect the circuit protector for continuity in ON and OFF positions.
Fuse Inspection
Procedure for visually inspecting and checking fuse continuity.
Regulator/Rectifier Inspection
Measures resistance between terminals to ensure compliance with specifications.
Engine Wire Harness Removal/Installation
Procedure for removing and installing the engine wire harness.
Cylinder Head/Valves
Tools
Lists specialized tools for cylinder head and valve service.
Cylinder Head Removal/Installation
Step-by-step guide for removing and installing the cylinder head.
Cylinder Head Disassembly/Assembly
Detailed instructions for disassembling and reassembling cylinder head components.
Cylinder Head/Valves Inspection
Procedures for inspecting cylinder compression, head warpage, and valve seat width.
Valve Guide I.D.
Method for measuring valve guide inside diameter after reaming.
Valve Face Inspection
How to inspect valve faces for irregularities.
Valve Stem O.D.
Procedure for measuring valve stem outside diameter for wear.
Guide-to-Stem Clearance
Calculating and checking valve guide-to-stem clearance.
Valve Spring Free Length
Method for measuring valve spring free length.
Valve Spring Perpendicularity
How to measure valve spring perpendicularity against the service limit.
Push Rod Runout
Procedure for checking push rods for wear and straightness.
Valve Guide Replacement
Instructions for replacing valve guides using heat and specialized tools.
Valve Guide Reaming
Procedure for reaming valve guides to ensure proper fit after replacement.
Valve Seat Reconditioning
Steps for cleaning, resurfacing, and lapping valve seats.
Crankcase
Tools
Lists specialized tools required for crankcase service.
Crankcase Cover Removal/Installation
Procedure for removing and installing the crankcase cover.
Crankshaft/Balancer/Piston Removal/Installation
Steps for removing and installing crankshaft, balancer weight, and piston assemblies.
Balancer Weight/Camshaft Installation
Procedure for installing the balancer weight and camshaft using timing marks.
1/2 or 1/6 Reduction Unit Disassembly/Assembly
Instructions for disassembling and assembling the reduction unit.
1/2 Reduction Unit (Chain Type) Disassembly/Assembly (GX240 Only)
Specific procedures for disassembling and assembling the chain-type reduction unit.
1/2 Reduction Unit With Clutch Disassembly/Assembly (GX270 Only)
Detailed steps for disassembling and reassembling the reduction unit with clutch.
Governor Disassembly/Assembly
Procedure for disassembling and assembling the governor system components.
Piston Disassembly/Assembly
Detailed steps for disassembling and assembling pistons, rings, and pins.
Crankcase Cover/Cylinder Barrel/Piston/Connecting Rod/Crankshaft/Camshaft Inspection
Inspection procedures for various internal engine components.
1/2 or 1/6 Reduction Unit Inspection
Inspection of components within the reduction unit, such as gears and bearings.
1/2 Reduction Unit (Chain Type) Inspection (GX240 Only)
Inspection of the chain-type reduction unit components.
1/2 Reduction Unit With Clutch Inspection (GX270 Only)
Inspection of components within the reduction unit with clutch.
GX240/GX270 Crankshaft/Balancer Weight Bearing/Oil Seal Replacement (Crankcase Cover Side)
Procedure for replacing crankshaft and balancer weight bearings and oil seals on the cover side.
GX340/GX390 Crankshaft/Balancer Weight Bearing/Oil Seal Replacement (Crankcase Cover Side)
Procedure for replacing crankshaft and balancer weight bearings and oil seals on the cover side.
GX240/GX270 Crankshaft Bearing Replacement (Flywheel Side)
Steps for replacing crankshaft bearings on the flywheel side.
GX340/GX390 Crankshaft Bearing Replacement (Flywheel Side)
Steps for replacing crankshaft bearings on the flywheel side.
GX270 Crankshaft/Balancer Weight Bearing/Oil Seal Replacement (Cylinder Barrel Side)
Procedure for replacing crankshaft and balancer weight bearings and oil seals on the cylinder barrel side.
GX340/GX390 Crankshaft/Balancer Weight Bearing/Oil Seal Replacement (Cylinder Barrel Side)
Procedure for replacing crankshaft and balancer weight bearings and oil seals on the cylinder barrel side.
Counter Shaft/P.T.O. Shaft Bearing/Oil Seal Replacement (Gear Case Cover Side)
Procedure for replacing counter shaft and P.T.O. shaft bearings/oil seals on the gear case cover side.
GX240/GX270 Counter Shaft/P.T.O. Shaft Bearing Replacement (Crankcase Cover Side)
Procedure for replacing counter shaft and P.T.O. shaft bearings on the crankcase cover side.
GX340/GX390 Counter Shaft/P.T.O. Shaft Bearing Replacement (Crankcase Cover Side)
Procedure for replacing counter shaft and P.T.O. shaft bearings on the crankcase cover side.
P.T.O. Shaft Bearing (6204)
Procedure for replacing the P.T.O. shaft bearing.
Muffler
Muffler Removal/Installation
Procedure for removing and installing the engine muffler assembly.
Muffler Cover Removal/Installation (If Equipped)
Steps for removing and installing the muffler cover.
Exhaust Pipe Stud Bolt Replacement
Procedure for replacing exhaust pipe stud bolts.
Wiring Diagrams
How to Read a Wiring Diagram & Related Information
Explains how to interpret wiring diagrams, connector drawings, and symbols.
No Charge Coil Type Wiring Diagram
Wiring diagram for engines without a charge coil.
1A/3A Charge Coil Type Wiring Diagram
Wiring diagram for engines with a 1A/3A charge coil.
10A Charge Coil Type Wiring Diagram
Wiring diagram for engines equipped with a 10A charge coil.
18A Charge Coil Type Wiring Diagram
Wiring diagram for engines equipped with an 18A charge coil.
Troubleshooting
Before Troubleshooting
Preliminary checks and precautions before starting troubleshooting procedures.
Troubleshooting: Engine Speed Issues
Diagnostic steps for problems where engine speed does not increase or stabilize.
Charging System
Charging System Diagram
Illustrates the electrical connections for charging systems.
Before Troubleshooting
Preliminary checks and precautions before diagnosing charging system issues.
Charging System Troubleshooting
Diagnostic flowcharts for common charging system problems.
Charge/Power Coil Removal/Installation
Procedure for removing and installing charge and power coils.
Charge/Power Coil Inspection
Methods for inspecting charge and power coils for resistance and continuity.
Other Electrical
Control Box Disassembly/Assembly
Detailed steps for disassembling and reassembling the control box.
Oil Level Switch Removal/Installation
Procedure for removing and installing the oil level switch.
Regulator/Rectifier Inspection
Measures resistance between terminals to ensure compliance with specifications.
Ignition System
System Diagram
Provides a schematic of the ignition system's electrical connections.
Ignition System Troubleshooting
Diagnostic steps for identifying and resolving ignition system faults.
Ignition Coil Removal/Installation
Procedure for removing and installing the ignition coil assembly.
Starting System
System Diagram
Illustrates the electrical schematic for the starting system.
Starting System Troubleshooting
Diagnostic steps for troubleshooting issues where the starter motor does not operate.
Recoil Starter Removal/Installation
Procedure for removing and installing the recoil starter assembly.
Recoil Starter Disassembly
Detailed steps for disassembling the recoil starter.
Recoil Starter Assembly
Instructions for assembling the recoil starter components.
Recoil Starter Inspection
Methods for inspecting recoil starter operation and components like the starter pulley.
Starter Motor Removal/Installation
Procedure for removing and installing the starter motor.
Starter Motor Disassembly/Assembly
Detailed steps for disassembling and reassembling the starter motor.
Inspection: Starter Motor Performance Test
Procedure for testing starter motor performance under load and no-load conditions.
Brush Replacement
Instructions for replacing worn starter motor brushes.
Other Electrical
Component Location
Identifies the location of key electrical components on the engine.
Control Box Removal/Installation
Procedure for removing and installing the engine's control box.
Control Box Disassembly/Assembly
Detailed steps for disassembling and reassembling the control box.
Oil Level Switch Removal/Installation
Procedure for removing and installing the oil level switch.
Oil Level Switch Inspection
How to inspect the oil level switch for continuity under different oil conditions.
Combination Switch Inspection
How to inspect the combination switch continuity at each position.
Indicator Inspection
Method for measuring resistance between the indicator terminal and plate.
Rectifier Inspection
Measures resistance between terminals to ensure compliance with specifications.
Cylinder Head/Valves
Cylinder Head Removal/Installation
Step-by-step guide for removing and installing the cylinder head.
Crankcase
Crankcase Cover Removal/Installation
Procedure for removing and installing the crankcase cover.
Crankshaft/Balancer/Piston Removal/Installation
Steps for removing and installing crankshaft, balancer weight, and piston assemblies.
Wiring Diagrams
Wiring Diagrams
Illustrates the electrical connections for various engine configurations.
Specifications
Serial Number Location
Identifies where serial, type, and description codes are stamped on the engine.
Type Code
Details various engine model type codes and their corresponding P.T.O. variations.
Dimensions and Weight Specifications
Provides dimensional and weight specifications for different engine models.
Engine Specifications
Lists key engine specifications such as displacement, bore, stroke, and power output.
Dimensional Drawings
Illustrates the physical dimensions of engine models.
P.T.O. Dimensional Drawings
Provides detailed drawings of Power Take-Off (P.T.O.) dimensions.
Service Information
Maintenance Standards
Details standard measurements and service limits for engine parts.
Torque Values
Lists specified torque values for engine bolts and nuts.
Lubrication & Seal Points
Identifies lubrication and seal points for various engine components.
Harness and Tube Routing
Illustrates the routing of engine wire harnesses and tubes for different types.
Troubleshooting
Before Troubleshooting
Preliminary checks and precautions before starting troubleshooting.
Troubleshooting: Engine Speed Issues
Diagnostic steps for problems where engine speed does not increase or stabilize.
Charging System
Charging System Diagram
Illustrates the electrical connections for charging systems.
Before Troubleshooting
Preliminary checks and precautions before diagnosing charging system issues.
Charging System Troubleshooting
Diagnostic flowcharts for common charging system problems.
Charge/Power Coil Removal/Installation
Procedure for removing and installing charge and power coils.
Charge/Power Coil Inspection
Methods for inspecting charge and power coils for resistance and continuity.
Other Electrical
Control Box Disassembly/Assembly
Detailed steps for disassembling and reassembling the control box.
Oil Level Switch Removal/Installation
Procedure for removing and installing the oil level switch.
Regulator/Rectifier Inspection
Measures resistance between terminals to ensure compliance with specifications.

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