Stihl BG55 Carburetor Adjustment (3 Pro Tips for Perfect Tuning)

Ah, the smell of two-stroke exhaust and freshly cut grass… It takes me back to my teenage years, helping my grandpa clear brush on his property. He had this trusty Stihl BG55 blower, and I remember him constantly fiddling with the carburetor. He’d say, “Gotta get her singing just right, boy!” Back then, I didn’t understand much about carburetors. Now, after years of tinkering with small engines, I know a thing or two. The user intent behind searching for “Stihl BG55 Carburetor Adjustment (3 Pro Tips for Perfect Tuning)” is clear: someone is having trouble with their blower’s performance and wants to optimize it through carburetor adjustments. This usually means the engine is running poorly, not starting easily, or lacking power.

So, let’s dive into the art of tuning a Stihl BG55 carburetor. It’s not rocket science, but precision and understanding are key. I’ll share my pro tips to help you get your blower running like new.

Understanding the Stihl BG55 Carburetor

Before we even touch a screwdriver, let’s understand what a carburetor does and why it’s so important.

The carburetor’s main job is to mix air and fuel in the correct ratio to create a combustible mixture for the engine. The Stihl BG55 uses a simple, yet effective, carburetor design. It relies on vacuum created by the engine’s piston movement to draw fuel from the fuel tank, atomize it, and mix it with air.

Key Components:

• Jets (High and Low): These are small, adjustable screws that control the amount of fuel entering the mixture. The “H” jet controls the high-speed fuel mixture, affecting performance at full throttle. The “L” jet controls the low-speed fuel mixture, impacting idle and acceleration.
• Idle Speed Screw: This screw adjusts the throttle plate position, controlling the engine’s idle speed.
• Throttle Linkage: This connects the throttle trigger to the carburetor, allowing you to control the engine’s speed.
• Fuel Inlet Needle Valve: Regulates fuel flow into the carburetor based on engine demand.

Why Carburetor Adjustment is Necessary:

Over time, several factors can throw off the carburetor’s delicate balance:

• Fuel Degradation: Old or contaminated fuel can clog jets and disrupt the fuel/air mixture.
• Altitude Changes: Air density changes with altitude, requiring carburetor adjustments for optimal performance.
• Engine Wear: As the engine wears, its fuel requirements may change, necessitating adjustments.
• Factory Settings: Sometimes, factory settings aren’t optimal for your specific operating conditions.

Green Wood vs. Seasoned Wood: A Quick Analogy

Think of green wood as a freshly tuned carburetor – full of potential but needing careful handling. Seasoned wood is like a perfectly adjusted carburetor – smooth, efficient, and reliable. Just as the right fuel/air mixture is crucial for engine performance, the right moisture content is essential for efficient burning in firewood. Green wood has a high moisture content (often above 50%), making it difficult to ignite and burn cleanly. Seasoned wood, on the other hand, has a moisture content below 20%, making it easier to light and producing more heat with less smoke.

Safety First!

Before you start fiddling with your BG55, remember safety.

• Wear Safety Glasses: Protect your eyes from flying debris and fuel splashes.
• Wear Gloves: Protect your hands from fuel and sharp edges.
• Work in a Well-Ventilated Area: Exhaust fumes are toxic.
• Allow the Engine to Cool: Avoid burns by working on a cool engine.
• Disconnect the Spark Plug Wire: Prevent accidental starting.

The Tools You’ll Need

Having the right tools makes the job much easier. Here’s what I recommend:

• Screwdriver Set: You’ll need a small, flat-head screwdriver to adjust the carburetor jets. A specialized carburetor adjustment tool is often required, as standard screwdrivers may not fit the jets. These tools are readily available online and at most small engine repair shops.
• Tachometer (Optional): A tachometer measures engine RPM (revolutions per minute) and helps you fine-tune the idle speed. While not essential, it’s a valuable tool for achieving optimal performance. I use a SENDEC tachometer that clips onto the spark plug wire.
• Spark Plug Wrench: To remove and inspect the spark plug.
• Carburetor Cleaner: To clean any debris from the jets.
• Compressed Air: To blow out the jets after cleaning.
• Shop Rags: For cleaning up spills.
• Fuel Stabilizer: To prevent fuel degradation. I always add STA-BIL to my fuel cans.

Pro Tip #1: The Listening Game – Diagnosing the Problem

Before you start turning screws, listen to your BG55. The engine’s sound can tell you a lot about what’s wrong. This is where my experience comes in handy. I’ve spent countless hours listening to engines, and I can often diagnose a problem just by the sound.

Common Symptoms and Their Causes:

• Engine Won’t Start: This could be due to a clogged fuel filter, a dirty spark plug, or a carburetor issue. If the engine isn’t getting fuel, the carburetor is a prime suspect.
• Engine Starts but Stalls Immediately: This often indicates a lean fuel mixture (too much air, not enough fuel). The low-speed jet (“L”) is likely the culprit.
• Engine Idles Rough or Stalls at Idle: Again, this points to a lean low-speed mixture or an improperly adjusted idle speed.
• Engine Lacks Power at Full Throttle: This suggests a lean high-speed mixture. The high-speed jet (“H”) needs adjustment.
• Engine Smokes Excessively: This could be due to a rich fuel mixture (too much fuel, not enough air). Both the “H” and “L” jets could be the cause.
• Engine Hesitates or Stumbles During Acceleration: This is often a sign of a lean transition from low-speed to high-speed. The low-speed jet needs fine-tuning.

The Spark Plug Tell-Tale:

The spark plug can provide valuable clues about the engine’s condition. Remove the spark plug and inspect it.

• Black and Sooty: Indicates a rich fuel mixture.
• White or Light Gray: Indicates a lean fuel mixture.
• Tan or Light Brown: Indicates a healthy fuel mixture.
• Wet: Indicates flooding (too much fuel).

Case Study: The Stihl That Wouldn’t Sing

I once had a Stihl chainsaw that refused to run at full throttle. It would start and idle fine, but as soon as I gave it full gas, it would bog down and die. After checking the fuel lines and spark plug, I suspected the carburetor. I listened closely to the engine and noticed a slight whistling sound at high RPMs, suggesting a lean condition. Sure enough, after carefully adjusting the high-speed jet, the chainsaw roared back to life.

Pro Tip #2: The Art of Adjustment – Step-by-Step Guide

Now that you have a better understanding of the carburetor and its symptoms, let’s get to the adjustment process.

Step 1: Locating the Adjustment Screws

The “H” (high-speed), “L” (low-speed), and idle speed screws are usually located on the side of the carburetor. They may be labeled with “H,” “L,” and “LA” (idle adjustment). Some carburetors have limiter caps on the adjustment screws to restrict the range of adjustment. These caps may need to be removed to achieve optimal tuning.

Step 2: Initial Settings

Before making any adjustments, it’s helpful to know the factory settings. These settings are usually listed in the Stihl BG55’s owner’s manual. If you don’t have the manual, a good starting point is to turn both the “H” and “L” screws all the way in (clockwise) until they gently seat, then back them out 1 to 1.5 turns. This is just a starting point; you’ll need to fine-tune from there.

Step 3: Starting the Engine

Start the engine and let it warm up for a few minutes. This is crucial, as the engine’s fuel requirements change as it warms up.

Step 4: Adjusting the Low-Speed Jet (“L”)

The low-speed jet affects the engine’s idle and acceleration. Here’s how to adjust it:

1. Idle Speed: First, adjust the idle speed screw (LA) to achieve a stable idle. The engine should idle smoothly without stalling. Aim for an idle speed around 2800-3200 RPM (check your manual for the exact specification). If you don’t have a tachometer, adjust the idle speed until the engine runs smoothly without the cutting head engaging.
2. Lean Best Idle: Now, slowly turn the low-speed jet (“L”) clockwise (leaner) until the engine starts to stumble or stall. Note the position of the screw.
3. Rich Best Idle: Next, slowly turn the low-speed jet counter-clockwise (richer) until the engine starts to stumble or smoke. Note the position of the screw.
4. The Sweet Spot: Turn the low-speed jet back to the midpoint between the lean and rich stumble points. This is your “lean best idle” – the point where the engine idles smoothly and responds quickly to throttle input.

Step 5: Adjusting the High-Speed Jet (“H”)

The high-speed jet affects the engine’s performance at full throttle. This adjustment is critical for preventing engine damage.

1. Full Throttle Test: With the engine warmed up and idling smoothly, gradually increase the throttle to full. Listen carefully to the engine’s sound.
2. Lean Condition: If the engine sounds “screaming” or “whining” at full throttle, it’s running lean. This is dangerous and can lead to engine damage. Immediately richen the mixture by turning the high-speed jet counter-clockwise.
3. Rich Condition: If the engine sounds “bogged down” or “sluggish” at full throttle, it’s running rich. Lean the mixture by turning the high-speed jet clockwise.
4. The Sweet Spot: The goal is to find the point where the engine runs smoothly and powerfully at full throttle without any signs of lean or rich running. A slight four-stroking sound (a “burbling” sound) at full throttle is often a sign of a slightly rich mixture, which is generally safer than a lean mixture.

Step 6: Fine-Tuning and Testing

After adjusting both the “H” and “L” jets, fine-tune the idle speed and test the engine’s performance. Start the engine, let it warm up, and then perform the following tests:

• Acceleration Test: Quickly open the throttle from idle to full. The engine should respond quickly and smoothly without hesitating or stumbling.
• Cutting Test: If you’re adjusting a chainsaw or brushcutter, make a few cuts in wood to test the engine’s performance under load. The engine should maintain its RPM without bogging down.

Important Note: Carburetor adjustment is an iterative process. You may need to make small adjustments to both the “H” and “L” jets to achieve optimal performance. Be patient and listen carefully to the engine.

Measurements, Tools, and Wood Types:

• Moisture Content of Firewood: Aim for a moisture content of 15-20% for optimal burning. Use a moisture meter to check. I use a Wagner MMC220.
• Chainsaw Bar Length: Choose a bar length appropriate for the size of the wood you’re cutting. A 16-inch bar is suitable for most firewood cutting.
• Axe Weight: A heavier axe (6-8 lbs) is better for splitting larger rounds, while a lighter axe (4-6 lbs) is easier to swing for smaller rounds. I prefer a Gransfors Bruks splitting axe.
• Wood Types: Hardwoods like oak, maple, and ash are ideal for firewood due to their high BTU (British Thermal Unit) content. Softwoods like pine and fir burn faster and produce less heat.
• Log Splitter Tonnage: Choose a log splitter with sufficient tonnage for the size and type of wood you’re splitting. A 20-ton splitter is adequate for most firewood needs.
• Stacking Height: Stack firewood no higher than 4 feet to prevent collapse.
• Drying Time: Allow firewood to season for at least 6-12 months before burning.

Case Study: The Bogging Brushcutter

A local landscaper brought me a Stihl brushcutter that was bogging down under load. He had already replaced the fuel filter and spark plug, but the problem persisted. After listening to the engine, I suspected a lean high-speed mixture. I carefully adjusted the high-speed jet, but the problem didn’t go away. Then, I noticed that the air filter was partially clogged. After cleaning the air filter and readjusting the high-speed jet, the brushcutter ran like a champ. This highlights the importance of checking all the basics before diving into carburetor adjustments.

Pro Tip #3: The Preventative Approach – Maintaining Carburetor Health

The best way to avoid carburetor problems is to prevent them in the first place. Here are some tips for maintaining carburetor health:

• Use Fresh Fuel: Old fuel can degrade and clog jets. Always use fresh fuel, and add a fuel stabilizer to prevent fuel degradation. I recommend using premium fuel with a high octane rating.
• Clean the Air Filter Regularly: A dirty air filter restricts airflow and can cause the engine to run rich. Clean the air filter every 25 hours of operation, or more often in dusty conditions.
• Check the Fuel Filter: A clogged fuel filter restricts fuel flow and can cause the engine to run lean. Replace the fuel filter annually, or more often if you suspect it’s clogged.
• Store the Blower Properly: When storing the blower for extended periods, drain the fuel tank and run the engine until it stalls to prevent fuel from gumming up the carburetor.
• Consider Carburetor Rebuild Kits: Over time, the carburetor’s internal components can wear out. A carburetor rebuild kit contains new gaskets, diaphragms, and other parts to restore the carburetor to like-new condition.

Strategic Advantages of Proper Carburetor Tuning:

• Improved Engine Performance: A properly tuned carburetor ensures optimal engine performance, resulting in more power and efficiency.
• Reduced Fuel Consumption: A lean-running engine consumes more fuel than a properly tuned engine.
• Extended Engine Life: A lean-running engine can overheat and suffer premature wear. Proper carburetor tuning prevents this.
• Reduced Emissions: A properly tuned engine produces fewer emissions.
• Easier Starting: A properly tuned carburetor makes the engine easier to start.

Cost Considerations:

• Carburetor Adjustment Tool: $10-$20
• Tachometer: $20-$50
• Carburetor Cleaner: $5-$10
• Fuel Stabilizer: $5-$10
• Carburetor Rebuild Kit: $20-$40

Skill Levels Required:

Carburetor adjustment requires some mechanical aptitude and patience. Beginners can learn the basics with practice, but more complex carburetor issues may require the expertise of a qualified small engine mechanic.

Timing Estimates:

Carburetor adjustment typically takes 30 minutes to an hour. Carburetor cleaning and rebuilding can take several hours.

Case Study: The Forgotten Fuel Stabilizer

A friend of mine stored his Stihl leaf blower for the winter without adding fuel stabilizer to the fuel tank. When he tried to start it in the spring, it wouldn’t start. The carburetor was completely gummed up with old fuel. He had to remove the carburetor, disassemble it, and clean all the jets with carburetor cleaner. It took him several hours to get the blower running again. This illustrates the importance of using fuel stabilizer when storing small engines.

Debarking Logs: A Related Skill

While we’re on the topic of wood processing, let’s briefly touch on debarking logs. Debarking is the process of removing the bark from logs. It’s often done to improve the drying time of firewood, prevent insect infestations, and create a cleaner burning fuel.

• Tools: Debarking can be done with a drawknife, a debarking spud, or a chainsaw.
• Technique: Use the drawknife or debarking spud to peel the bark off the log. Be careful not to damage the wood underneath. With a chainsaw, carefully score the bark and then pry it off with a pry bar.
• Benefits: Debarked logs dry faster, are less susceptible to insect infestations, and burn cleaner.

Firewood Stacking: The Art of Cordwood

Proper firewood stacking is essential for efficient drying and storage.

• Location: Choose a sunny, well-ventilated location for your firewood stack.
• Base: Elevate the firewood off the ground using pallets or scrap wood.
• Stacking Pattern: Stack the firewood in a crisscross pattern to promote airflow.
• Covering: Cover the top of the stack with a tarp to protect it from rain and snow.
• Aesthetics: Consider stacking your firewood in a decorative pattern for visual appeal. Cordwood construction is an ancient building technique using short logs stacked crosswise with mortar.

Next Steps: Putting Knowledge into Action

Now that you’ve learned the basics of Stihl BG55 carburetor adjustment, it’s time to put your knowledge into action.

1. Gather Your Tools: Assemble the necessary tools and safety gear.
2. Diagnose the Problem: Listen to your blower and identify the symptoms.
3. Adjust the Carburetor: Follow the step-by-step guide to adjust the “H” and “L” jets.
4. Test and Fine-Tune: Test the engine’s performance and fine-tune the carburetor as needed.
5. Maintain Your Blower: Use fresh fuel, clean the air filter, and check the fuel filter regularly.

Remember, carburetor adjustment is a skill that takes time and practice to master. Don’t be afraid to experiment and learn from your mistakes. If you’re unsure about any step, consult a qualified small engine mechanic.

The satisfaction of getting a small engine running smoothly is immense. It’s a testament to your skills and knowledge. And, just like my grandpa taught me, it’s about getting that engine to “sing just right.” Good luck, and happy tuning!

Learn more