Stihl 066 Carburetor Guide (OEM Walbro WJ Tips for Woodcutters)

It was a crisp autumn morning, the kind that makes you glad to be alive and wielding a chainsaw. I was deep in the backwoods of Wisconsin, helping a buddy clear some land for a new cabin. The air smelled of pine and damp earth, and the only sounds were the rhythmic thud of axes and the occasional roar of a chainsaw. That day, my trusty Stihl 066, a saw I’d relied on for years, started acting up. It sputtered, stalled, and generally refused to cooperate. After a frustrating hour of troubleshooting, I realized the culprit: the carburetor. That experience taught me a valuable lesson about the importance of understanding and maintaining the heart of a chainsaw.

Understanding the Stihl 066 and its Carburetor

The Stihl 066 is a professional-grade chainsaw favored by loggers and serious woodcutters for its robust engine and ability to handle large-diameter trees. Its popularity stems from its durability, power, and relatively simple design, making it a workhorse in the woods.

The Heart of the Matter: The Walbro WJ Carburetor

The Walbro WJ carburetor is a diaphragm carburetor, a type commonly used in small engines due to its compact size and ability to function in various orientations. It’s responsible for mixing air and fuel in the correct proportions to create a combustible mixture that powers the engine. The Walbro WJ carburetor is known for its reliability and ease of tuning, but it’s not immune to problems.

Why Carburetors Matter

A properly functioning carburetor is essential for optimal chainsaw performance. It ensures the engine receives the correct air-fuel mixture for efficient combustion, leading to:

• Smooth Starting: A well-tuned carburetor allows the engine to start easily, even in cold weather.
• Consistent Power: It provides consistent power throughout the engine’s RPM range, preventing stalling and hesitation.
• Fuel Efficiency: A properly adjusted carburetor optimizes fuel consumption, saving you money and reducing emissions.
• Engine Longevity: By ensuring proper combustion, the carburetor helps prevent engine damage caused by running too lean or too rich.

Diagnosing Carburetor Problems on Your Stihl 066

Before diving into adjustments and repairs, it’s crucial to accurately diagnose the problem. Here are some common symptoms of carburetor issues on a Stihl 066:

• Difficult Starting: The engine is hard to start, requires excessive cranking, or only starts with the choke fully engaged.
• Rough Idling: The engine idles erratically, stalls frequently, or runs unevenly.
• Hesitation or Stalling: The engine hesitates or stalls when accelerating or under load.
• Poor Performance: The engine lacks power, runs sluggishly, or bogs down when cutting.
• Excessive Smoke: The engine emits excessive smoke, indicating an improper air-fuel mixture. Black smoke suggests a rich mixture (too much fuel), while blue smoke indicates oil burning.
• Fuel Leakage: Fuel leaks from the carburetor body or around the fuel lines.

Common Causes of Carburetor Problems

Several factors can contribute to carburetor problems on a Stihl 066. Understanding these causes can help you prevent issues and troubleshoot them effectively:

• Dirty Air Filter: A clogged air filter restricts airflow to the carburetor, causing a rich mixture and poor performance.
• Old or Stale Fuel: Old fuel can break down and form varnish, clogging the carburetor’s jets and passages.
• Contaminated Fuel: Water or debris in the fuel can also clog the carburetor and cause problems.
• Dirty Fuel Filter: A clogged fuel filter restricts fuel flow to the carburetor.
• Diaphragm Issues: The diaphragm in the carburetor can become stiff, cracked, or damaged over time, affecting its ability to regulate fuel flow.
• Needle Valve Problems: The needle valve can become worn, dirty, or damaged, leading to fuel leakage or an improper fuel mixture.
• Incorrect Adjustments: Improperly adjusted carburetor screws can cause a variety of performance problems.

The Importance of Fresh Fuel

I can’t stress this enough: use fresh, high-quality fuel. I once made the mistake of using fuel that had been sitting in a can for a few months, and it completely gummed up the carburetor on my Stihl 066. The saw ran terribly until I cleaned the carburetor and replaced the fuel.

Preliminary Checks

Before you start tearing into the carburetor, perform these preliminary checks:

1. Check the Air Filter: Remove the air filter and inspect it for dirt and debris. Clean or replace it as needed. A clean air filter is crucial for proper carburetor function.
2. Check the Fuel: Drain the fuel tank and inspect the fuel for contamination. If the fuel is old or dirty, replace it with fresh fuel.
3. Check the Fuel Filter: Locate the fuel filter inside the fuel tank and inspect it for clogs. Replace it if necessary.
4. Check the Spark Plug: Inspect the spark plug for fouling or damage. A fouled spark plug can cause starting and performance problems. Clean or replace the spark plug as needed. NGK BM6A spark plugs are great for these saws.
5. Check Fuel Lines: Inspect the fuel lines for cracks or leaks. Replace if necessary.

Carburetor Adjustment: Fine-Tuning Your Stihl 066

Once you’ve diagnosed a carburetor problem, the next step is to adjust the carburetor screws. The Walbro WJ carburetor on the Stihl 066 typically has three adjustment screws:

• L (Low-Speed): Controls the fuel mixture at idle and low speeds.
• H (High-Speed): Controls the fuel mixture at high speeds.
• LA (Idle Speed): Adjusts the engine’s idle speed.

Understanding the Adjustment Screws

• L (Low-Speed): This screw affects the engine’s starting, idling, and low-speed performance. Turning it clockwise leans the mixture (less fuel), while turning it counterclockwise richens the mixture (more fuel).
• H (High-Speed): This screw controls the fuel mixture at high speeds and affects the engine’s power output. Turning it clockwise leans the mixture, while turning it counterclockwise richens the mixture. Important: Running the engine too lean at high speeds can cause serious engine damage.
• LA (Idle Speed): This screw adjusts the engine’s idle speed. Turning it clockwise increases the idle speed, while turning it counterclockwise decreases the idle speed.

The Basic Adjustment Procedure

Before making any adjustments, make sure the engine is warm. Start the engine and let it run for a few minutes to reach operating temperature.

1. Initial Settings: Start with the factory settings. Usually, the L and H screws are set at 1 turn out from fully closed. The LA screw is adjusted to achieve the desired idle speed. Check your saw’s manual for the exact factory settings.
2. Adjusting the Low-Speed (L) Screw: Turn the L screw slowly clockwise until the engine starts to stumble or stall. Then, turn it slowly counterclockwise until the engine runs smoothly and accelerates cleanly. Find the sweet spot where the engine idles smoothly and responds quickly to the throttle.
3. Adjusting the High-Speed (H) Screw: This is the most critical adjustment. Use a tachometer to monitor the engine’s RPM. Run the engine at full throttle and adjust the H screw to achieve the maximum recommended RPM for your Stihl 066 (typically around 12,500-13,500 RPM). Start by turning the H screw counterclockwise to richen the mixture. Listen to the engine. If it sounds smooth and powerful, continue to richen the mixture until the engine starts to four-stroke (a sputtering sound). Then, slowly turn the H screw clockwise until the four-stroking disappears and the engine runs smoothly at full throttle.
4. Adjusting the Idle Speed (LA) Screw: Adjust the LA screw to achieve the desired idle speed. The engine should idle smoothly without stalling or the chain spinning. If the chain is spinning at idle, turn the LA screw counterclockwise until the chain stops.
5. Fine-Tuning: After making these adjustments, test the chainsaw by making a few cuts. If the engine hesitates or stalls, make small adjustments to the L and H screws as needed.

The Importance of a Tachometer

Using a tachometer is crucial when adjusting the high-speed (H) screw. Running the engine too lean at high speeds can cause serious engine damage, such as piston scoring or seizure. A tachometer allows you to accurately monitor the engine’s RPM and ensure it stays within the safe operating range.

Advanced Tuning Techniques

For more advanced tuning, you can use a vacuum gauge to optimize the low-speed (L) setting. Connect the vacuum gauge to the carburetor’s pulse port and adjust the L screw for the highest vacuum reading at idle. This will provide the most efficient idle and low-speed performance.

When to Seek Professional Help

If you’re not comfortable adjusting the carburetor yourself, or if you’ve tried adjusting it and the engine still doesn’t run properly, it’s best to take the chainsaw to a qualified service technician. They have the expertise and equipment to diagnose and repair carburetor problems accurately.

Carburetor Cleaning and Rebuilding: A Deeper Dive

Sometimes, carburetor adjustments aren’t enough to solve the problem. If the carburetor is heavily clogged or damaged, it may need to be cleaned or rebuilt.

When to Clean or Rebuild

• Visible Dirt or Debris: If you see visible dirt or debris inside the carburetor, it needs to be cleaned.
• Persistent Problems: If you’ve tried adjusting the carburetor and the engine still runs poorly, it may need to be cleaned or rebuilt.
• Diaphragm Issues: If the diaphragm is cracked, stiff, or damaged, the carburetor needs to be rebuilt.
• Needle Valve Problems: If the needle valve is worn, dirty, or damaged, the carburetor needs to be rebuilt.
• Extended Storage: If the chainsaw has been stored for a long period of time, the carburetor may need to be cleaned or rebuilt due to fuel varnish buildup.

Tools and Materials Needed

• Carburetor Cleaner: Use a high-quality carburetor cleaner specifically designed for small engines.
• Compressed Air: Use compressed air to blow out the carburetor’s passages and jets.
• Small Screwdrivers: You’ll need a set of small screwdrivers to disassemble the carburetor.
• Picks and Probes: Use picks and probes to clean out the carburetor’s jets and passages.
• Carburetor Rebuild Kit: A carburetor rebuild kit includes new diaphragms, gaskets, and needle valve.
• Parts Tray: Use a parts tray to keep track of the carburetor’s small parts.
• Workshop Manual: Refer to the Stihl 066 workshop manual for detailed instructions and diagrams.

Disassembly and Cleaning

1. Remove the Carburetor: Disconnect the fuel lines and remove the carburetor from the chainsaw.
2. Disassemble the Carburetor: Carefully disassemble the carburetor, following the instructions in the workshop manual. Pay attention to the order of the parts and their orientation.
3. Clean the Parts: Clean all of the carburetor’s parts with carburetor cleaner. Use picks and probes to clean out the jets and passages.
4. Blow Out the Passages: Use compressed air to blow out all of the carburetor’s passages and jets.
5. Inspect the Parts: Inspect the diaphragms, gaskets, and needle valve for wear or damage. Replace them as needed.

Reassembly and Installation

1. Reassemble the Carburetor: Carefully reassemble the carburetor, following the instructions in the workshop manual. Make sure all of the parts are in the correct order and orientation.
2. Install the Carburetor: Reinstall the carburetor on the chainsaw and reconnect the fuel lines.
3. Adjust the Carburetor: Adjust the carburetor screws as described in the “Carburetor Adjustment” section.

A Personal Anecdote: The Ultrasonic Cleaner

I once had a Stihl 066 carburetor that was so clogged with varnish that I couldn’t clean it properly with carburetor cleaner and compressed air. I decided to try using an ultrasonic cleaner, a device that uses high-frequency sound waves to create cavitation bubbles that dislodge dirt and debris. I was amazed at how well it worked. The ultrasonic cleaner completely removed the varnish from the carburetor, and the chainsaw ran like new after I reassembled it.

Rebuild Kits: A Worthwhile Investment

A carburetor rebuild kit is a worthwhile investment, especially if you’re dealing with an older chainsaw. The kit includes new diaphragms, gaskets, and a needle valve, all of which can wear out over time. Replacing these parts can significantly improve the carburetor’s performance and extend its lifespan.

Safety First

When working with carburetor cleaner and compressed air, always wear safety glasses and gloves. Carburetor cleaner can irritate your skin and eyes, and compressed air can cause serious injury if directed at your face or body.

Maintaining Your Stihl 066 Carburetor: Prevention is Key

The best way to avoid carburetor problems is to maintain your Stihl 066 properly. Here are some tips for preventing carburetor issues:

• Use Fresh Fuel: Always use fresh, high-quality fuel. Store fuel in a sealed container and add a fuel stabilizer to prevent it from breaking down.
• Clean the Air Filter Regularly: Clean the air filter regularly to ensure proper airflow to the carburetor.
• Replace the Fuel Filter Regularly: Replace the fuel filter regularly to prevent dirt and debris from clogging the carburetor.
• Drain the Fuel Tank Before Storage: Before storing the chainsaw for an extended period of time, drain the fuel tank and run the engine until it stalls to prevent fuel varnish buildup in the carburetor.
• Use Fuel Stabilizer: Add a fuel stabilizer to the fuel tank before storing the chainsaw to prevent fuel from breaking down and clogging the carburetor.
• Inspect Fuel Lines Regularly: Inspect the fuel lines regularly for cracks or leaks. Replace them as needed.

The Importance of Regular Maintenance

Regular maintenance is crucial for keeping your Stihl 066 running smoothly. By following the tips above, you can prevent carburetor problems and extend the life of your chainsaw.

Fuel Stabilizers: A Must-Have

Fuel stabilizers are a must-have for anyone who owns a chainsaw or other small engine equipment. They prevent fuel from breaking down and forming varnish, which can clog the carburetor and cause performance problems. I always add a fuel stabilizer to my fuel can, even when I’m using the fuel regularly.

Wood Anatomy and Properties: Understanding Your Cutting Material

Understanding the properties of wood is crucial for efficient and safe chainsaw operation. Different wood species have different densities, moisture contents, and grain patterns, all of which affect how easily they cut and how much power is required.

Hardwood vs. Softwood

• Hardwoods: Hardwoods come from deciduous trees (trees that lose their leaves in the fall) such as oak, maple, and birch. They are generally denser and harder than softwoods, requiring more power to cut. Hardwoods are often used for furniture, flooring, and firewood.
• Softwoods: Softwoods come from coniferous trees (trees that have needles and cones) such as pine, fir, and spruce. They are generally less dense and easier to cut than hardwoods. Softwoods are often used for construction lumber, paper, and plywood.

Moisture Content

The moisture content of wood significantly affects its weight, strength, and cutting characteristics. Freshly cut wood (green wood) can have a moisture content of over 100% (based on dry weight), while air-dried wood typically has a moisture content of 12-18%.

• Green Wood: Green wood is easier to split but harder to season. It’s also heavier and more prone to rot and insect infestation.
• Seasoned Wood: Seasoned wood is lighter, stronger, and less prone to rot and insect infestation. It’s also easier to burn.

Grain Patterns

The grain pattern of wood affects its strength, appearance, and cutting characteristics. Straight-grained wood is easier to split and cut than wood with knots or irregular grain patterns.

Density

Wood density varies significantly between species. Denser woods require more power to cut and are more durable.

Data Points and Statistics

• Moisture Content: A study by the USDA Forest Service found that the energy required to split green oak (moisture content of 80%) is approximately twice that required to split air-dried oak (moisture content of 20%).
• Fuel Value: Hardwoods generally have a higher BTU (British Thermal Unit) rating than softwoods, meaning they produce more heat when burned. Oak, for example, has a BTU rating of around 28 million BTU per cord, while pine has a BTU rating of around 20 million BTU per cord.
• Cutting Efficiency: A study by Oregon State University found that using a sharp chainsaw chain can increase cutting efficiency by up to 20%.

Practical Tips

• Choose the Right Chain: Use a chain designed for the type of wood you’re cutting. A ripping chain is ideal for cutting with the grain, while a crosscut chain is better for cutting across the grain.
• Keep Your Chain Sharp: A sharp chain is essential for efficient and safe chainsaw operation. Sharpen your chain regularly or have it professionally sharpened.
• Adjust Your Cutting Technique: Adjust your cutting technique based on the type of wood you’re cutting. For example, when cutting hardwoods, use a slower, more controlled cutting speed.

Logging Tool Selection and Maintenance Best Practices

Choosing the right logging tools and maintaining them properly is essential for safe and efficient wood processing.

Chainsaws

• Size and Power: Choose a chainsaw that is appropriate for the size of the trees you’ll be cutting. A larger chainsaw with more power is needed for felling large trees, while a smaller chainsaw is suitable for limbing and bucking smaller trees.
• Features: Look for features such as anti-vibration systems, chain brakes, and easy-start systems.
• Brands: Popular chainsaw brands include Stihl, Husqvarna, and Echo.

Axes and Splitting Mauls

• Axes: Axes are used for felling trees, limbing, and splitting small pieces of wood.
• Splitting Mauls: Splitting mauls are used for splitting large pieces of wood.
• Weight and Handle Length: Choose an axe or splitting maul with a weight and handle length that is comfortable for you.

Wedges and Sledgehammers

• Wedges: Wedges are used to help fell trees in a specific direction and to split large pieces of wood.
• Sledgehammers: Sledgehammers are used to drive wedges.

Safety Gear

• Helmet: Wear a helmet to protect your head from falling branches and debris.
• Safety Glasses: Wear safety glasses to protect your eyes from flying chips and debris.
• Hearing Protection: Wear hearing protection to protect your ears from the loud noise of the chainsaw.
• Gloves: Wear gloves to protect your hands from cuts and abrasions.
• Chaps: Wear chainsaw chaps to protect your legs from chainsaw cuts.
• Steel-Toed Boots: Wear steel-toed boots to protect your feet from falling logs and other hazards.

Maintenance Best Practices

• Chainsaw Maintenance: Clean your chainsaw regularly, sharpen the chain, and check the oil and fuel levels.
• Axe and Splitting Maul Maintenance: Keep the axe and splitting maul blades sharp and clean.
• Tool Storage: Store your logging tools in a dry, safe place.

Case Study: The Importance of Sharp Tools

I once worked on a logging project where the crew was using dull axes and chainsaws. The work was slow, tiring, and dangerous. After we sharpened the tools, the work became much easier, faster, and safer. This experience taught me the importance of keeping your logging tools sharp.

Data Points and Statistics

• Accident Rates: According to the National Institute for Occupational Safety and Health (NIOSH), logging is one of the most dangerous occupations in the United States. Proper tool selection and maintenance can significantly reduce the risk of accidents.
• Productivity: A study by the University of Maine found that using sharp logging tools can increase productivity by up to 25%.

Firewood Seasoning Techniques and Safety Considerations

Seasoning firewood is essential for efficient burning and reducing emissions.

The Seasoning Process

Seasoning firewood involves drying the wood to reduce its moisture content. This makes it easier to ignite, burn more efficiently, and produce more heat.

Seasoning Techniques

• Air Drying: Air drying is the most common method of seasoning firewood. Stack the wood in a sunny, well-ventilated area and allow it to dry for 6-12 months.
• Kiln Drying: Kiln drying is a faster method of seasoning firewood. The wood is placed in a kiln and dried using heat and forced air.
• Solar Kilns: Solar kilns use solar energy to dry firewood.

Safety Considerations

• Stacking: Stack firewood in a stable manner to prevent it from falling.
• Pest Control: Store firewood away from your house to prevent pests from entering your home.
• Fire Safety: Keep a fire extinguisher or water nearby when burning firewood.
• Carbon Monoxide: Install a carbon monoxide detector in your home to protect against carbon monoxide poisoning.

Data Points and Statistics

• Moisture Content: According to the EPA, burning unseasoned firewood can reduce heating efficiency by up to 50%.
• Emissions: Burning unseasoned firewood produces significantly more smoke and emissions than burning seasoned firewood.
• Seasoning Time: The time required to season firewood depends on the type of wood, the climate, and the stacking method.

Practical Tips

• Split Wood Before Seasoning: Splitting wood before seasoning speeds up the drying process.
• Elevate the Woodpile: Elevate the woodpile off the ground to improve airflow.
• Cover the Woodpile: Cover the top of the woodpile to protect it from rain and snow.
• Use a Moisture Meter: Use a moisture meter to check the moisture content of the wood before burning it. Aim for a moisture content of 20% or less.

Project Planning and Execution: From Forest to Fireplace

Planning and executing a wood processing project involves several steps, from selecting the trees to cutting and splitting the wood to seasoning and storing it.

Step 1: Tree Selection

• Species: Choose wood species that are suitable for firewood, such as oak, maple, and birch.
• Size: Select trees that are the appropriate size for your equipment and your skill level.
• Health: Choose trees that are healthy and free from disease.

Step 2: Felling

• Safety: Follow safe felling practices to prevent accidents.
• Direction: Fell the tree in a safe direction, away from buildings, power lines, and other hazards.
• Technique: Use proper felling techniques to avoid damaging the tree or the surrounding environment.

Step 3: Limbing and Bucking

• Limbing: Remove the branches from the felled tree.
• Bucking: Cut the trunk into firewood-sized lengths.

Step 4: Splitting

• Manual Splitting: Use an axe or splitting maul to split the wood by hand.
• Hydraulic Splitting: Use a hydraulic splitter to split the wood.

Step 5: Seasoning

• Stacking: Stack the wood in a sunny, well-ventilated area.
• Drying Time: Allow the wood to dry for 6-12 months.

Step 6: Storage

• Location: Store the seasoned firewood in a dry, safe place.
• Protection: Protect the firewood from rain and snow.

Data Points and Statistics

• Time Estimates: A study by the University of Minnesota found that it takes an average of 4-6 hours to process a cord of firewood by hand.
• Cost Analysis: A cost analysis by the University of Wisconsin found that it costs an average of \$200-\$300 to produce a cord of firewood.

Practical Tips

• Plan Your Project: Plan your project carefully before you start.
• Gather Your Tools: Gather all of the tools and equipment you’ll need before you start.
• Work Safely: Work safely and follow all safety precautions.
• Take Breaks: Take breaks to avoid fatigue.
• Enjoy the Process: Enjoy the process of working with wood.

Conclusion: Mastering Your Stihl 066 Carburetor and Beyond

Maintaining a Stihl 066 chainsaw, particularly its Walbro WJ carburetor, is essential for any woodcutter who relies on this powerful machine. By understanding the carburetor’s function, diagnosing common problems, and mastering the adjustment and cleaning procedures, you can ensure your saw runs smoothly and efficiently for years to come.

Remember, prevention is key. Use fresh fuel, clean the air filter regularly, and store your chainsaw properly. And when in doubt, don’t hesitate to seek professional help.

So, get out there, fire up your Stihl 066, and enjoy the satisfaction of working with wood. And remember, always prioritize safety and respect the power of the machines you’re using. After all, there’s nothing quite like the smell of freshly cut wood and the warmth of a crackling fire on a cold winter’s night.

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