Carb for Stihl FS55R Trimmer (5 Pro Tips to Boost Performance)

Ever find yourself wrestling with a Stihl FS55R trimmer that just won’t purr like it used to? It sputters, stalls, and generally acts like it’s got a serious case of the Mondays? Chances are, the culprit is lurking within the carburetor.

As someone who’s spent countless hours felling trees, bucking logs, and splitting firewood, I’ve learned a thing or two about keeping my equipment in tip-top shape. And believe me, a well-tuned carburetor is the heart and soul of any small engine, especially on a hardworking tool like the FS55R.

Understanding the Stihl FS55R Carburetor: A Deep Dive

Before we jump into the tips, let’s lay the groundwork with a solid understanding of what a carburetor actually does and how it functions in the FS55R.

What is a Carburetor, Anyway?

At its core, a carburetor is a mechanical device that mixes air and fuel to create a combustible mixture for the engine. In the Stihl FS55R, which uses a two-stroke engine, this mixture is crucial for smooth operation and optimal power. The carburetor’s job is to deliver the right air-fuel ratio under varying conditions, from idling to full throttle.

The Anatomy of the FS55R Carburetor

While carburetors can seem complex, they’re built on relatively simple principles. Here are the key components of the FS55R carburetor:

• Fuel Inlet: This is where the fuel enters the carburetor from the fuel tank. A small filter is usually located here to prevent debris from entering the system.
• Float Chamber: This chamber maintains a consistent fuel level. A float, similar to the one in your toilet tank, rises and falls with the fuel level, controlling a needle valve that regulates fuel flow.
• Main Jet: The main jet controls the amount of fuel delivered at higher engine speeds. It’s a small, precisely sized opening that meters the fuel flow.
• Idle Jet: The idle jet controls the fuel mixture at idle and low engine speeds.
• Throttle Valve: The throttle valve, controlled by the throttle trigger, regulates the amount of air entering the carburetor. More air means more power.
• Choke: The choke restricts airflow into the carburetor, creating a richer fuel mixture for cold starting.
• Adjustment Screws (H and L): These screws allow you to fine-tune the high-speed (H) and low-speed (L) fuel mixture settings.

How the Carburetor Works in the FS55R

Here’s a simplified explanation of the process:

1. Fuel Delivery: Fuel is drawn from the fuel tank into the float chamber. The float maintains a constant fuel level.
2. Air Intake: Air enters the carburetor through the air filter and venturi (a narrow passage that increases air velocity).
3. Mixing: As air rushes through the venturi, it creates a vacuum that draws fuel from the jets (either the idle jet or main jet, depending on the throttle position). The fuel mixes with the air to form a fine mist.
4. Delivery to Engine: The air-fuel mixture is drawn into the engine’s cylinder, where it’s compressed and ignited, powering the trimmer.

Common Carburetor Problems in the FS55R

Understanding how the carburetor works helps us diagnose common issues:

• Clogged Jets: Debris in the fuel can clog the tiny jets, restricting fuel flow.
• Sticking Float: A sticking float can cause the float chamber to overfill or underfill, leading to a rich or lean fuel mixture.
• Air Leaks: Air leaks around the carburetor or intake manifold can disrupt the air-fuel ratio, causing performance problems.
• Diaphragm Issues: Some carburetors use a diaphragm instead of a float. These diaphragms can become stiff or cracked over time, affecting fuel delivery.
• Incorrect Adjustments: Improperly adjusted H and L screws can lead to poor performance, stalling, or difficulty starting.

Tip #1: Master the Art of Carburetor Cleaning

A clean carburetor is a happy carburetor. This is probably the most crucial step in boosting your FS55R’s performance. Over time, fuel residue, dirt, and other contaminants can build up inside the carburetor, clogging jets and restricting fuel flow.

Why Cleaning is Essential

Think of your carburetor like a tiny, intricate plumbing system. Just like pipes in your house, it can get clogged with gunk. A clogged carburetor can lead to:

• Hard Starting: The engine struggles to get the right fuel mixture to start.
• Poor Idle: The engine stalls or idles erratically.
• Lack of Power: The engine doesn’t have the power it should, especially at higher speeds.
• Stalling: The engine stalls frequently, especially under load.
• Increased Fuel Consumption: The engine runs inefficiently, wasting fuel.

The Step-by-Step Cleaning Process

Here’s how I tackle carburetor cleaning on my FS55R:

1. Gather Your Supplies:
   • Carburetor Cleaner: Use a specialized carburetor cleaner. Don’t use brake cleaner or other harsh chemicals, as they can damage the carburetor’s rubber components.
   • Small Screwdrivers: You’ll need a set of small screwdrivers, including a flathead and Phillips head.
   • Needle-Nose Pliers: For removing small parts.
   • Compressed Air: Essential for blowing out jets and passages.
   • Soft Brush: A small brush, like an old toothbrush, for scrubbing.
   • Safety Glasses: Protect your eyes from cleaner and debris.
   • Gloves: Protect your hands from the cleaner.
   • Clean Work Area: Work in a well-ventilated area and protect your work surface.
2. Remove the Carburetor:
   • Disconnect the Fuel Line: Carefully disconnect the fuel line from the carburetor. Use pliers to loosen the fuel line clamp if necessary. Have a rag handy to catch any spilled fuel.
   • Disconnect the Throttle Linkage: Disconnect the throttle linkage from the carburetor.
   • Remove the Carburetor Mounting Bolts: Remove the bolts that secure the carburetor to the engine.
   • Carefully Remove the Carburetor: Gently remove the carburetor from the engine.
3. Disassemble the Carburetor:
   • Note the Orientation: Before you start disassembling, take photos or make notes of how the parts fit together. This will make reassembly much easier.
   • Remove the Adjustment Screws: Carefully remove the H and L adjustment screws. Note how many turns it takes to remove each screw completely. This will give you a starting point for re-adjusting the carburetor later.
   • Remove the Float Bowl: Remove the float bowl (the small bowl at the bottom of the carburetor). Be careful not to damage the gasket.
   • Remove the Float and Needle Valve: Remove the float and needle valve. The needle valve is a small, pointed valve that controls fuel flow into the float bowl.
   • Remove the Jets: Use a small screwdriver to remove the main jet and idle jet.
   • Remove Other Components: Remove any other removable components, such as the choke plate and throttle plate.
4. Clean the Components:
   • Soak the Components: Soak all the metal components in carburetor cleaner for at least 30 minutes.
   • Scrub the Components: Use a soft brush to scrub the components, removing any dirt or residue.
   • Clean the Jets: Use a thin wire or a carburetor cleaning tool to clean the jets. Make sure the openings are clear. You can also use compressed air to blow out the jets.
   • Clean the Carburetor Body: Use carburetor cleaner and a brush to clean the carburetor body. Pay special attention to the passages and orifices.
5. Rinse and Dry:
   • Rinse the Components: Rinse all the components with clean carburetor cleaner.
   • Dry the Components: Dry the components with compressed air or a clean cloth.
6. Reassemble the Carburetor:
   • Reassemble in Reverse Order: Reassemble the carburetor in the reverse order of disassembly.
   • Install the Jets: Install the main jet and idle jet. Make sure they are tightened securely.
   • Install the Float and Needle Valve: Install the float and needle valve. Make sure the float moves freely.
   • Install the Float Bowl: Install the float bowl. Make sure the gasket is in good condition.
   • Install the Adjustment Screws: Install the H and L adjustment screws. Turn them in until they are lightly seated, then back them out the number of turns you noted during disassembly.
   • Install Other Components: Install any other components you removed, such as the choke plate and throttle plate.
7. Reinstall the Carburetor:
   • Reinstall the Carburetor: Reinstall the carburetor on the engine.
   • Connect the Fuel Line: Connect the fuel line to the carburetor.
   • Connect the Throttle Linkage: Connect the throttle linkage to the carburetor.
   • Tighten the Mounting Bolts: Tighten the bolts that secure the carburetor to the engine.

Pro Tips for Cleaning

• Use a Carburetor Cleaning Kit: These kits often come with small brushes and wires that are perfect for cleaning the tiny passages in the carburetor.
• Pay Attention to the Jets: The jets are the most likely components to get clogged. Make sure they are completely clean and free of debris.
• Replace the Fuel Filter: While you’re at it, replace the fuel filter to prevent future clogs.
• Consider an Ultrasonic Cleaner: For heavily soiled carburetors, an ultrasonic cleaner can work wonders. These devices use sound waves to agitate the cleaning solution and remove stubborn deposits.

My Personal Experience

I remember one time, my FS55R was running terribly. It would start, but it would stall as soon as I gave it any throttle. I tried everything – new spark plug, fresh fuel – but nothing seemed to work. Finally, I decided to take apart the carburetor and give it a thorough cleaning.

What I found inside was shocking. The jets were completely clogged with a thick, black gunk. After a good soaking and scrubbing, the carburetor looked like new. I reassembled it, put it back on the trimmer, and fired it up. To my amazement, it ran perfectly! It was like a brand new machine. That experience taught me the importance of regular carburetor cleaning.

Tip #2: Master Carburetor Adjustment for Peak Performance

Once your carburetor is clean, the next step is to adjust it properly. This is where things can get a bit tricky, but with a little patience and understanding, you can fine-tune your FS55R for optimal performance.

Understanding the H and L Screws

The H and L screws control the fuel mixture at high speed (H) and low speed (L). Adjusting these screws affects the engine’s performance, fuel efficiency, and overall health.

• H Screw (High Speed): This screw controls the fuel mixture when the throttle is fully open. Adjusting the H screw affects the engine’s power and top speed.
• L Screw (Low Speed): This screw controls the fuel mixture at idle and low throttle settings. Adjusting the L screw affects the engine’s idle speed and throttle response.

The Adjustment Procedure

Here’s a step-by-step guide to adjusting the carburetor:

1. Warm Up the Engine: Start the engine and let it warm up for a few minutes. This is important because the engine needs to be at operating temperature for accurate adjustments.
2. Find the Starting Point: As I mentioned earlier, when you disassembled the carburetor, you should have noted how many turns it took to remove the H and L screws completely. This is your starting point. Turn the screws in until they are lightly seated, then back them out the number of turns you noted. If you didn’t note the number of turns, a good starting point is usually 1 to 1.5 turns out from lightly seated.
3. Adjust the L Screw (Low Speed):
   • Idle Speed: Turn the L screw in or out until the engine idles smoothly without stalling. If the engine idles too fast, turn the idle speed screw (usually marked with a “T”) counterclockwise to reduce the idle speed.
   • Throttle Response: Once the idle speed is set correctly, test the throttle response. Quickly open the throttle. If the engine hesitates or bogs down, turn the L screw out slightly (richen the mixture). If the engine revs up quickly but sputters or smokes, turn the L screw in slightly (lean the mixture).
4. Adjust the H Screw (High Speed):
   • Full Throttle: Open the throttle fully. Listen to the engine. If the engine sounds strained or weak, turn the H screw out slightly (richen the mixture). If the engine sputters or smokes, turn the H screw in slightly (lean the mixture).
   • Maximum RPM: The goal is to find the point where the engine runs smoothly and produces maximum power at full throttle. You can use a tachometer to measure the engine’s RPM. Consult your FS55R’s manual for the recommended maximum RPM.
5. Fine-Tune: After adjusting both the L and H screws, fine-tune them until the engine runs smoothly at all throttle settings. You may need to go back and forth between the two screws to get it just right.
6. Test Under Load: Finally, test the trimmer under load. Use it to trim some grass or weeds. If the engine stalls or bogs down under load, you may need to make further adjustments.

Troubleshooting Adjustment Issues

• Engine Stalls at Idle: If the engine stalls at idle, the L screw is probably set too lean. Turn the L screw out slightly to richen the mixture.
• Engine Bogs Down When Accelerating: If the engine bogs down when you accelerate, the L screw is probably set too lean. Turn the L screw out slightly to richen the mixture.
• Engine Sputters at High Speed: If the engine sputters at high speed, the H screw is probably set too rich. Turn the H screw in slightly to lean the mixture.
• Engine Smokes Excessively: If the engine smokes excessively, the fuel mixture is probably too rich. Turn both the L and H screws in slightly to lean the mixture.

Important Considerations

• Altitude: Altitude affects the air-fuel ratio. At higher altitudes, the air is thinner, so you may need to lean out the mixture by turning the H and L screws in slightly.
• Temperature: Temperature also affects the air-fuel ratio. In colder weather, the air is denser, so you may need to richen the mixture by turning the H and L screws out slightly.
• Fuel Type: Using the wrong type of fuel can also affect the air-fuel ratio. Always use the fuel recommended by Stihl.
• Listen to the Engine: The best way to adjust the carburetor is to listen to the engine. Learn to recognize the sounds of a lean mixture (strained, weak) and a rich mixture (sputtering, smoking).

My Personal Experience

I’ll never forget the time I spent hours trying to adjust the carburetor on my FS55R. I was convinced I was doing everything right, but the engine just wouldn’t run properly. It would either stall at idle or bog down when I tried to accelerate.

Finally, I decided to call a friend who was a small engine mechanic. He came over and, within minutes, had the carburetor adjusted perfectly. He explained that I wasn’t listening to the engine closely enough. He showed me how to recognize the subtle differences in sound between a lean mixture and a rich mixture.

That experience taught me the importance of patience and attention to detail when adjusting a carburetor. It also taught me the value of seeking help from someone who knows what they’re doing.

Tip #3: Inspect and Maintain Fuel Lines and Filters

Your carburetor can be sparkling clean and perfectly adjusted, but if the fuel supply is compromised, you’re still going to have problems. Fuel lines and filters are often overlooked, but they play a critical role in delivering clean, consistent fuel to the carburetor.

Why Fuel Lines and Filters Matter

• Fuel Lines: Fuel lines can crack, dry rot, or become clogged over time. This can restrict fuel flow, leading to poor performance or engine failure.
• Fuel Filters: Fuel filters prevent dirt, debris, and water from entering the carburetor. A clogged fuel filter can starve the engine of fuel.

Inspection and Maintenance

Here’s how to inspect and maintain your fuel lines and filters:

1. Fuel Lines:
   • Visual Inspection: Regularly inspect the fuel lines for cracks, leaks, or signs of wear. Pay special attention to the areas where the fuel lines connect to the fuel tank, carburetor, and fuel filter.
   • Flex Test: Gently flex the fuel lines. If they feel stiff or brittle, they need to be replaced.
   • Replace as Needed: Replace fuel lines that are cracked, leaking, or showing signs of wear. Use fuel lines that are specifically designed for small engines.
2. Fuel Filters:
   • Location: The fuel filter is usually located inside the fuel tank, attached to the end of the fuel line. Some models may have an inline fuel filter.
   • Inspection: Remove the fuel filter and inspect it. If it’s dirty or clogged, it needs to be cleaned or replaced.
   • Cleaning: Some fuel filters can be cleaned with carburetor cleaner. However, it’s usually best to replace the fuel filter.
   • Replacement: Replace the fuel filter at least once a year, or more often if you use your FS55R frequently or if you use fuel that is not fresh.

Pro Tips for Fuel Line and Filter Maintenance

• Use Fresh Fuel: Always use fresh fuel. Fuel that has been sitting for more than a month can start to break down and form gum and varnish, which can clog fuel lines and filters.
• Use Fuel Stabilizer: If you’re going to store your FS55R for an extended period, add fuel stabilizer to the fuel tank. This will help prevent the fuel from breaking down.
• Check the Fuel Tank Vent: The fuel tank vent allows air to enter the fuel tank as fuel is used. If the vent is clogged, it can create a vacuum in the fuel tank, preventing fuel from flowing to the carburetor. Make sure the fuel tank vent is clear.

My Personal Experience

I once had an FS55R that would start and run for a few minutes, then stall. I checked the carburetor, the spark plug, and everything else I could think of, but I couldn’t figure out what was wrong.

Finally, I decided to check the fuel filter. When I pulled it out of the fuel tank, it was completely clogged with a black, slimy substance. I replaced the fuel filter, and the trimmer ran perfectly!

That experience taught me that even a small, inexpensive part like a fuel filter can have a big impact on the performance of your FS55R.

Tip #4: Address Air Leaks for Smooth Operation

Air leaks are insidious enemies of small engines. They disrupt the delicate balance of the air-fuel mixture, leading to a host of performance problems. Finding and fixing air leaks is crucial for maximizing the performance of your Stihl FS55R.

How Air Leaks Affect Performance

Air leaks can cause a variety of problems, including:

• Lean Mixture: Air leaks allow extra air to enter the engine, creating a lean mixture (too much air, not enough fuel).
• Hard Starting: A lean mixture can make it difficult to start the engine.
• Poor Idle: A lean mixture can cause the engine to idle erratically or stall.
• Lack of Power: A lean mixture can reduce the engine’s power, especially at high speeds.
• Overheating: A lean mixture can cause the engine to overheat, which can damage the engine.

Common Sources of Air Leaks

• Carburetor Mounting Gasket: The gasket between the carburetor and the engine can dry out and crack, allowing air to leak in.
• Intake Manifold Gasket: The gasket between the intake manifold and the engine can also dry out and crack.
• Crankshaft Seals: The crankshaft seals prevent air from leaking into the crankcase. These seals can wear out over time, especially on older engines.
• Fuel Lines: Cracks in the fuel lines can allow air to be sucked into the fuel system.
• Impulse Line: The impulse line connects the crankcase to the carburetor and provides a pressure pulse that helps pump fuel. If this line is cracked or damaged, it can leak air.

Finding Air Leaks

Finding air leaks can be challenging, but here are a few techniques:

1. Visual Inspection: Carefully inspect all the potential sources of air leaks, looking for cracks, loose connections, or signs of wear.
2. Spray Test: Start the engine and let it idle. Spray carburetor cleaner or starting fluid around the carburetor mounting gasket, intake manifold gasket, crankshaft seals, and fuel lines. If the engine speed changes when you spray a particular area, you’ve found an air leak.
3. Smoke Test: A smoke test is a more sophisticated method of finding air leaks. It involves using a smoke machine to inject smoke into the engine. Any leaks will be revealed by the smoke escaping.

Fixing Air Leaks

• Replace Gaskets: Replace any gaskets that are cracked, damaged, or worn. Use new gaskets that are specifically designed for your FS55R.
• Tighten Connections: Tighten any loose connections, such as the carburetor mounting bolts and intake manifold bolts.
• Replace Fuel Lines: Replace any fuel lines that are cracked or damaged.
• Replace Crankshaft Seals: Replacing crankshaft seals is a more involved process that may require special tools. If you’re not comfortable doing it yourself, take your FS55R to a qualified mechanic.

My Personal Experience

I had an FS55R that was running lean. It was hard to start, it idled poorly, and it lacked power. I checked the carburetor, the fuel lines, and everything else I could think of, but I couldn’t find the problem.

Finally, I decided to do a spray test. I started the engine and sprayed carburetor cleaner around the carburetor mounting gasket. When I sprayed a particular spot, the engine speed suddenly increased. I had found an air leak!

I replaced the carburetor mounting gasket, and the trimmer ran perfectly. That experience taught me the importance of checking for air leaks when troubleshooting engine problems.

Tip #5: Regular Maintenance for Long-Term Reliability

The key to keeping your Stihl FS55R running smoothly for years to come is regular maintenance. Preventative maintenance is far more cost-effective and less time-consuming than dealing with major repairs.

The Importance of Regular Maintenance

• Prolonged Lifespan: Regular maintenance can significantly extend the life of your FS55R.
• Optimal Performance: A well-maintained trimmer will run more efficiently and produce more power.
• Reduced Downtime: Regular maintenance can help prevent breakdowns and reduce downtime.
• Cost Savings: Preventative maintenance is usually less expensive than major repairs.

Key Maintenance Tasks

1. Air Filter:
   • Cleaning: Clean the air filter regularly, especially if you’re working in dusty conditions. Use compressed air to blow out the filter.
   • Replacement: Replace the air filter at least once a year, or more often if it’s heavily soiled.
2. Spark Plug:
   • Inspection: Inspect the spark plug regularly. Look for signs of wear, fouling, or damage.
   • Cleaning: Clean the spark plug with a wire brush.
   • Replacement: Replace the spark plug at least once a year, or more often if it’s fouled or damaged.
3. Fuel System:
   • Fuel Filter: Replace the fuel filter at least once a year.
   • Fuel Lines: Inspect the fuel lines regularly for cracks or leaks. Replace them as needed.
   • Fuel Tank: Clean the fuel tank periodically to remove any sediment or debris.
4. Carburetor:
   • Cleaning: Clean the carburetor at least once a year, or more often if you’re experiencing performance problems.
   • Adjustment: Adjust the carburetor as needed to maintain optimal performance.
5. Lubrication:
   • Gear Head: Lubricate the gear head (the part of the trimmer that drives the cutting head) regularly with grease.
   • Moving Parts: Lubricate any other moving parts, such as the throttle linkage, with oil.
6. Storage:
   • Fuel Stabilization: If you’re going to store your FS55R for an extended period, add fuel stabilizer to the fuel tank.
   • Empty the Fuel Tank: Alternatively, you can empty the fuel tank completely.
   • Clean the Trimmer: Clean the trimmer thoroughly before storing it.
   • Store in a Dry Place: Store the trimmer in a dry place, away from direct sunlight and extreme temperatures.

Creating a Maintenance Schedule

Create a maintenance schedule and stick to it. This will help you stay on top of your maintenance tasks and ensure that your FS55R is always in top condition.

Here’s a sample maintenance schedule:

• Every Use:
  • Check the air filter.
  • Check the fuel level.
  • Check the cutting head.
• Monthly:
  • Clean the air filter.
  • Inspect the spark plug.
  • Lubricate the gear head.
• Annually:
  • Replace the air filter.
  • Replace the spark plug.
  • Replace the fuel filter.
  • Clean the carburetor.
  • Inspect the fuel lines.

My Personal Experience

I’ve learned the hard way that neglecting maintenance can lead to big problems. I used to be pretty lax about maintaining my FS55R. I would only clean the air filter when it was visibly dirty, and I would only replace the spark plug when the engine started running poorly.

As a result, my FS55R suffered a number of breakdowns. I had to replace the carburetor, the fuel lines, and even the engine itself.

After that experience, I became a firm believer in regular maintenance. I now follow a strict maintenance schedule, and my FS55R runs like a champ. It starts easily, it idles smoothly, and it has plenty of power.

Conclusion: Unleash the Full Potential of Your FS55R

By mastering these five pro tips – carburetor cleaning, adjustment, fuel system maintenance, air leak detection, and regular upkeep – you’ll unlock the full potential of your Stihl FS55R trimmer. You’ll experience smoother starts, more power, improved fuel efficiency, and a longer lifespan for your trusty tool.

Remember, a little preventative maintenance goes a long way. Take the time to care for your FS55R, and it will reward you with years of reliable service. Now, get out there and make some sawdust!

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