How to Start Stihl Weed Wacker (Troubleshoot FS 55R Startup Issues)
1. Preliminary Checks: Fuel, Spark, and Air – The Three Pillars of Combustion
Before diving into more complex troubleshooting, let’s cover the basics. These are the most common culprits and often the easiest to fix.
- Fuel: Is there fuel in the tank? Seems obvious, right? But I’ve been caught out before, convinced there was gas when the tank was near empty. Old fuel is another common issue. Gasoline degrades over time, especially when mixed with oil. This stale fuel can clog the carburetor and prevent the engine from starting. I always recommend using fresh fuel, mixed according to the manufacturer’s specifications (usually 50:1 for Stihl). If the fuel has been sitting for more than a month, drain it and replace it with fresh fuel.
- Spark: Is the spark plug firing? Remove the spark plug (make sure the engine is off and cool!) and inspect it. It should be clean and dry. If it’s wet, the engine might be flooded. If it’s fouled with carbon deposits, clean it with a wire brush or replace it. To test for spark, reattach the spark plug to the spark plug wire, ground the metal part of the plug against the engine block, and pull the starter cord. You should see a strong, consistent spark. If not, replace the spark plug. A faulty spark plug is a very common cause of starting problems.
- Air: Is the air filter clean? A clogged air filter restricts airflow to the engine, making it difficult to start. Remove the air filter and inspect it. If it’s dirty, clean it with soap and water (foam filters) or replace it (paper filters). Allow the filter to dry completely before reinstalling it. I’ve seen engines completely fail to start due to a severely clogged air filter.
2. Understanding the Stihl FS 55R Starting Procedure
The Stihl FS 55R has a specific starting procedure that needs to be followed. Deviating from this procedure can lead to starting problems.
- Choke Position: The choke enriches the fuel mixture to help the engine start when it’s cold. The FS 55R typically has three choke positions: full choke, half choke (or run position), and off.
- Cold Start: For a cold engine, start with the choke in the full choke position. Pull the starter cord until the engine sputters or tries to start. Then, move the choke to the half choke (run) position and pull the starter cord again.
- Warm Start: For a warm engine, start with the choke in the half choke (run) position. You may not need to use the choke at all if the engine is already warm.
- Throttle Position: The throttle should be in the idle position when starting. Avoid holding the throttle open while starting, as this can flood the engine.
- Primer Bulb: Some Stihl FS 55R models have a primer bulb. Press the primer bulb several times to prime the carburetor before starting. This draws fuel into the carburetor and makes it easier to start the engine.
3. Diagnosing Carburetor Issues
The carburetor is the heart of the fuel system, and it’s a common source of starting problems.
- Clogged Carburetor: The carburetor can become clogged with debris, especially if you’re using old fuel. This can restrict fuel flow and prevent the engine from starting.
- Symptoms: Hard starting, rough idling, stalling, lack of power.
- Troubleshooting: Remove the carburetor and inspect it for debris. Clean the carburetor with carburetor cleaner. Pay close attention to the jets and passages. You may need to use a small wire or needle to clear any blockages.
- My Experience: I once had a Stihl FS 55R that wouldn’t start no matter what I did. I cleaned the carburetor several times, but it still wouldn’t run. Finally, I discovered a tiny piece of debris lodged in one of the jets. Once I removed it, the engine started right up. It’s often the smallest things that cause the biggest problems.
- Carburetor Adjustment: The carburetor has adjustment screws that control the fuel/air mixture. If these screws are not properly adjusted, the engine may not start.
- Symptoms: Hard starting, rough idling, stalling, lack of power.
- Troubleshooting: Refer to the Stihl FS 55R service manual for the proper carburetor adjustment procedure. The basic procedure is to turn the high (H) and low (L) speed adjustment screws in until they lightly seat, then back them out to the manufacturer’s recommended setting (typically 1 to 1.5 turns). Fine-tune the adjustments until the engine runs smoothly at both idle and high speed.
- Leaking Carburetor: A leaking carburetor can cause fuel to flood the engine, making it difficult to start.
- Symptoms: Fuel leaking from the carburetor, wet spark plug, strong fuel odor.
- Troubleshooting: Inspect the carburetor for leaks. Check the fuel lines and connections for cracks or damage. Replace any damaged parts. The carburetor gasket might also be damaged and need replacement.
4. Fuel System Inspection: Lines, Filter, and Tank Vent
The fuel system is responsible for delivering fuel from the tank to the carburetor. Problems in the fuel system can prevent the engine from starting.
- Fuel Lines: Inspect the fuel lines for cracks, leaks, or kinks. Replace any damaged fuel lines. Over time, fuel lines can become brittle and crack, leading to fuel leaks and air leaks.
- My Tip: When replacing fuel lines, use fuel-resistant tubing specifically designed for small engines.
- Fuel Filter: The fuel filter prevents debris from entering the carburetor. A clogged fuel filter can restrict fuel flow and prevent the engine from starting.
- Symptoms: Hard starting, lack of power, stalling.
- Troubleshooting: Remove the fuel filter from the fuel tank and inspect it. If it’s dirty, replace it. Fuel filters are inexpensive and should be replaced regularly.
- 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 tank, preventing fuel from flowing to the carburetor.
- Symptoms: Hard starting, stalling, engine dies after running for a short time.
- Troubleshooting: Remove the fuel cap and try starting the engine. If it starts, the fuel tank vent is likely clogged. Clean the vent with a small wire or needle.
5. Ignition System Checks: Coil and Flywheel
The ignition system generates the spark that ignites the fuel/air mixture in the engine. Problems in the ignition system can prevent the engine from starting.
- Ignition Coil: The ignition coil generates the high-voltage spark that ignites the fuel/air mixture. A faulty ignition coil can prevent the engine from starting.
- Symptoms: No spark, weak spark, intermittent spark.
- Troubleshooting: Test the ignition coil with a multimeter. Check the resistance of the primary and secondary windings. Refer to the Stihl FS 55R service manual for the proper resistance values. If the ignition coil is faulty, replace it.
- Caution: Working with the ignition system involves high voltage. Be careful to avoid electric shock.
- Flywheel: The flywheel is a rotating component that generates the electricity for the ignition system. A damaged or improperly positioned flywheel can prevent the engine from starting.
- Symptoms: No spark, weak spark, engine won’t turn over.
- Troubleshooting: Inspect the flywheel for damage. Check the air gap between the flywheel and the ignition coil. The air gap should be set according to the Stihl FS 55R service manual. If the flywheel is damaged or the air gap is incorrect, adjust or replace the flywheel.
6. Compression Testing: A Sign of Engine Health
Compression is essential for the engine to run. Low compression can indicate worn piston rings, a damaged cylinder, or a leaky valve.
- Symptoms: Hard starting, lack of power, engine won’t start.
- Troubleshooting: Use a compression tester to measure the compression in the cylinder. Refer to the Stihl FS 55R service manual for the proper compression value. If the compression is low, the engine may need to be rebuilt.
- My Advice: While compression testing can be a bit more involved, it’s crucial for diagnosing serious engine problems. It’s a good idea to have a mechanic perform this test if you’re not comfortable doing it yourself.
7. Flooding: The Over-Enthusiastic Fuel Supply
Flooding occurs when too much fuel enters the cylinder, making it difficult for the engine to ignite.
- Symptoms: Wet spark plug, strong fuel odor, engine won’t start.
- Troubleshooting: Remove the spark plug and pull the starter cord several times to clear the excess fuel from the cylinder. Allow the cylinder to air out for a few minutes. Reinstall the spark plug and try starting the engine with the choke in the off position.
- Prevention: Avoid over-priming the engine. Use the choke sparingly.
8. Exhaust System: Clearing the Path
A blocked exhaust can create back pressure, preventing the engine from starting or running properly.
- Symptoms: Hard starting, lack of power, engine stalls easily.
- Troubleshooting: Remove the muffler and inspect it for blockages. Clean the muffler with a wire brush or replace it. Also, check the exhaust port on the cylinder head for carbon buildup.
- My Observation: I once encountered a weed wacker that wouldn’t start, and after checking everything else, I discovered a wasp nest in the muffler! It’s always worth a quick look.
9. Starter Mechanism: The Link to the Engine
The starter mechanism is responsible for turning the engine over. Problems with the starter mechanism can prevent the engine from starting.
- Symptoms: Starter cord won’t pull, starter cord pulls but doesn’t engage the engine.
- Troubleshooting: Inspect the starter cord for damage. Check the starter pawls and spring for wear or breakage. Replace any damaged parts. Lubricate the starter mechanism with a light oil.
10. Case Studies and Real-World Examples
Let’s look at some specific scenarios I’ve encountered over the years.
- Case Study 1: The Stihl FS 55R That Wouldn’t Idle. A friend brought me his FS 55R complaining that it would start, but wouldn’t idle. I cleaned the carburetor, replaced the fuel filter, and checked the spark plug, but the problem persisted. Finally, I noticed that the low-speed adjustment screw on the carburetor was completely closed. I opened the screw to the manufacturer’s recommended setting, and the engine idled perfectly. Lesson learned: always check the carburetor adjustments.
- Case Study 2: The Intermittent Spark. I was working on an FS 55R that would start sometimes, but not others. I suspected a faulty ignition coil. I tested the coil with a multimeter, and it seemed to be within specifications. However, I noticed that the spark plug wire was loose. I tightened the wire, and the engine started consistently. Lesson learned: check the simple things first.
- Case Study 3: The Fuel Line Mystery. A customer brought in an FS 55R that was leaking fuel. I inspected the fuel lines and found a small crack near the fuel tank. I replaced the fuel line, and the leak was gone. However, the engine still wouldn’t start. I then realized that the fuel line had collapsed internally, restricting fuel flow. I replaced the fuel line again with a higher-quality fuel line, and the engine started right up. Lesson learned: use high-quality replacement parts.
11. Preventive Maintenance: Avoiding Future Headaches
Preventive maintenance is key to keeping your Stihl FS 55R running smoothly and avoiding starting problems.
- If you’re not comfortable working on small engines.
- If you’ve tried all the troubleshooting steps and the engine still won’t start.
- If you suspect a serious engine problem, such as low compression.
- If you don’t have the necessary tools or equipment.
A qualified small engine mechanic can diagnose and repair the problem quickly and efficiently.
13. Final Thoughts: Persistence and Patience
Troubleshooting small engine problems can be frustrating, but with persistence and patience, you can usually find the solution. Remember to follow a systematic approach, check the simple things first, and don’t be afraid to ask for help. With a little effort, you can get your Stihl FS 55R back up and running and get back to your yard work.
By following these steps, you should be able to diagnose and fix most starting problems with your Stihl FS 55R weed wacker. Good luck, and happy trimming!
