Stihl Trimmer Will Not Start: Fix Tips For Woodcutting Pros (3 Hacks)

Let’s dive into the frustrating but common problem of a Stihl trimmer refusing to start. As someone who’s spent years felling trees, processing timber, and prepping firewood, I know how crucial these tools are. A dead trimmer can throw a wrench into your entire workflow. The good news is, many starting issues are easily fixed with a few simple checks. I’ll share my experiences and provide a step-by-step guide, along with some “hacks” I’ve learned over the years, to get your Stihl trimmer roaring back to life. We’ll cover everything from basic troubleshooting to more in-depth diagnostics, ensuring you’re equipped to tackle this problem head-on.

Stihl Trimmer Won’t Start: Fix Tips for Woodcutting Pros (3 Hacks)

A non-starting Stihl trimmer can be incredibly frustrating, especially when you’re on a tight schedule. Whether you’re clearing brush around a logging site, maintaining trails for firewood access, or simply keeping your yard tidy, a reliable trimmer is essential. In my experience, most starting problems stem from a handful of common issues. Let’s break down the troubleshooting process and explore some proven solutions.

Understanding the Basics: Two-Stroke Engines and Trimmers

Before we dive into the fixes, let’s briefly cover some key concepts. Stihl trimmers, like most handheld power equipment, typically use two-stroke engines. These engines require a precise mixture of gasoline and oil to lubricate the internal components. Key terms to understand include:

Fuel Mixture: The ratio of gasoline to oil, usually specified by the manufacturer (often 50:1). Using the wrong mixture can lead to engine damage or starting problems.
Carburetor: The component that mixes air and fuel in the correct proportions for combustion.
Spark Plug: The device that ignites the air-fuel mixture in the cylinder.
Air Filter: Prevents dirt and debris from entering the engine.
Fuel Filter: Prevents contaminants from entering the carburetor.
Primer Bulb: A small bulb that, when pressed, draws fuel from the tank into the carburetor, making starting easier.
Choke: A valve that restricts airflow to the carburetor, creating a richer fuel mixture for cold starts.

Knowing these terms will help you understand the troubleshooting steps and the underlying causes of starting problems.

Step 1: The Obvious Checks – Fuel, Spark, and Air

The first step in troubleshooting any engine problem is to check the basics: fuel, spark, and air.

Fuel Check

Fuel Tank Level: This might seem obvious, but it’s the first thing I always check. Make sure there’s sufficient fuel in the tank. I’ve been caught out more than once, assuming there was enough fuel only to find it was bone dry.
Fuel Mixture: Verify that you’re using the correct fuel mixture (gasoline and two-stroke oil). Stihl typically recommends a 50:1 ratio. Using straight gasoline or an incorrect mixture can cause serious engine damage. I once saw a colleague ruin a brand-new trimmer by using the wrong fuel mixture – a costly mistake.
Fuel Quality: Stale fuel can cause starting problems. Gasoline degrades over time, especially when mixed with oil. If the fuel has been sitting in the tank for more than a month, it’s best to drain it and refill with fresh fuel. I always recommend using fuel stabilizer, especially if you don’t use your trimmer frequently. This helps prevent fuel degradation and keeps the carburetor clean.
Fuel Cap Vent: The fuel cap has a small vent that allows air to enter the tank as fuel is used. If this vent is clogged, it can create a vacuum in the tank, preventing fuel from flowing to the carburetor. Try loosening the fuel cap slightly. If the trimmer starts, the vent is likely clogged. Clean or replace the fuel cap.
Fuel Line Inspection: Carefully inspect the fuel lines for cracks, leaks, or kinks. A cracked fuel line can allow air to enter the fuel system, preventing the trimmer from starting. Replace any damaged fuel lines.

Spark Check

Spark Plug Condition: Remove the spark plug and inspect it. Look for signs of fouling (carbon buildup), cracking, or damage. A fouled spark plug won’t produce a strong spark. Clean the spark plug with a wire brush or replace it. I always keep a spare spark plug on hand. It’s a cheap and easy way to eliminate a potential problem.
Spark Plug Gap: The spark plug gap is the distance between the electrode and the ground electrode. A gap that’s too wide or too narrow can prevent the spark plug from firing correctly. Use a spark plug gap tool to ensure the gap is within the manufacturer’s specifications (usually around 0.020-0.025 inches or 0.5-0.6 mm).
Spark Test: Connect the spark plug to the spark plug wire and ground the spark plug against the engine block. Pull the starter cord. You should see a strong, blue spark. If there’s no spark or the spark is weak and yellow, the ignition system may be faulty. This could be a problem with the ignition coil or the spark plug wire. I have used an inline spark tester before and it makes the process much more efficient.
Spark Plug Type: Make sure you are using the correct spark plug for your Stihl trimmer model. Using the wrong spark plug can cause starting problems or even engine damage.

Air Check

Air Filter Condition: A dirty 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 or replace it. I prefer to replace the air filter regularly, especially when working in dusty environments.
Air Filter Type: There are typically two types of air filters: foam and paper. Foam filters can be cleaned and reused, while paper filters should be replaced when dirty.
Air Filter Housing: Make sure the air filter housing is properly sealed. A loose or damaged housing can allow dirt and debris to enter the engine, even with a clean air filter.

Step 2: Carburetor Issues and Solutions

If the fuel, spark, and air checks are all good, the problem likely lies with the carburetor. The carburetor is responsible for mixing air and fuel in the correct proportions for combustion. Carburetor problems are a common cause of starting issues in small engines.

Primer Bulb Check

Primer Bulb Operation: The primer bulb is a small, clear bulb that you press to draw fuel into the carburetor. When you press the primer bulb, you should see fuel flowing through the fuel lines. If the primer bulb is cracked or damaged, it won’t function properly. Replace the primer bulb if necessary.
Primer Bulb Function: Make sure the primer bulb is actually priming the engine. Press it several times and check if fuel is flowing into the carburetor. If not, there may be a blockage in the fuel lines or the carburetor.

Choke Operation

Choke Position: The choke restricts airflow to the carburetor, creating a richer fuel mixture for cold starts. Make sure the choke is in the correct position for starting (usually fully closed). Once the engine starts, gradually open the choke.
Choke Linkage: Check the choke linkage to ensure it’s moving freely and that the choke valve is opening and closing properly. A sticky or damaged choke linkage can prevent the choke from functioning correctly.

Carburetor Cleaning

External Cleaning: Start by cleaning the outside of the carburetor with carburetor cleaner. This will remove any dirt or debris that could be interfering with its operation.
Internal Cleaning: If the trimmer still won’t start, you may need to clean the carburetor internally. This involves disassembling the carburetor and cleaning the jets and passages with carburetor cleaner and compressed air. This can be a delicate process, so it’s best to consult a repair manual or watch a video tutorial before attempting it.
Carburetor Adjustment: After cleaning the carburetor, you may need to adjust the idle speed and the high-speed mixture. These adjustments are typically made using small screws on the carburetor. Refer to your owner’s manual for the correct settings. I always recommend making small adjustments and testing the engine after each adjustment.

Carburetor Replacement

When to Replace: If cleaning and adjusting the carburetor doesn’t solve the problem, it may be necessary to replace it. Carburetors can wear out over time, especially if they’re not properly maintained.
Carburetor Kits: You can often purchase carburetor rebuild kits that include all the necessary parts to overhaul your carburetor. However, if you’re not comfortable working on small engines, it’s best to replace the entire carburetor.

Step 3: Exhaust System Inspection

A clogged exhaust system can also prevent a trimmer from starting. The exhaust system allows exhaust gases to escape from the engine. If the exhaust port or muffler is clogged with carbon buildup, it can restrict airflow and prevent the engine from starting.

Exhaust Port Cleaning

Location: The exhaust port is located on the cylinder head, where the exhaust manifold attaches.
Cleaning Procedure: Remove the exhaust manifold and inspect the exhaust port. If it’s clogged with carbon buildup, use a scraper or wire brush to clean it. Be careful not to damage the cylinder head.

Muffler Cleaning

Muffler Removal: Remove the muffler from the engine.
Cleaning Procedure: Inspect the muffler for carbon buildup. You can clean the muffler by soaking it in carburetor cleaner or by using a torch to burn off the carbon. Be careful when using a torch, as the muffler can get very hot.

Hack #1: The Quick Start Trick – Starter Fluid

Sometimes, a quick shot of starting fluid can help get a stubborn engine running. This is especially useful if the engine is flooded or if the fuel system is having trouble drawing fuel.

How to Use: Remove the air filter and spray a small amount of starting fluid into the carburetor intake. Replace the air filter and try to start the engine.
Caution: Use starting fluid sparingly. Excessive use of starting fluid can damage the engine.
Underlying Issue: This is a temporary solution. If you need to use starting fluid frequently, there’s likely an underlying problem with the fuel system that needs to be addressed.

Hack #2: The Heat Gun Method – For Cold Weather Starts

In cold weather, it can be difficult to start a small engine. The fuel doesn’t vaporize as easily, and the engine components are cold. A heat gun can help warm up the engine and make it easier to start.

How to Use: Use a heat gun to gently warm up the carburetor and the cylinder head. Be careful not to overheat the engine.
Caution: Don’t use a heat gun near flammable materials.
Alternative: If you don’t have a heat gun, you can try using a hair dryer.

Hack #3: The “Burp” Technique – Clearing a Flooded Engine

If you’ve been trying to start the engine repeatedly and it’s not starting, it may be flooded with fuel. The “burp” technique can help clear a flooded engine.

How to Use: Remove the spark plug and pull the starter cord several times to clear the cylinder of excess fuel. Replace the spark plug and try to start the engine.
Alternative: You can also try turning the engine upside down to drain the excess fuel from the cylinder.
Caution: Be careful not to spill fuel on yourself or on the ground.

Case Study 1: Reviving a Neglected Stihl FS 56 RC-E

I once inherited a Stihl FS 56 RC-E trimmer that had been sitting in a shed for years. It was in rough shape, covered in dust and grime. Unsurprisingly, it wouldn’t start. Here’s how I brought it back to life:

Initial Assessment: I started by checking the fuel tank. The fuel was old and smelled terrible. I drained the tank and refilled it with fresh fuel and two-stroke oil.
Air Filter: The air filter was completely clogged with dirt and debris. I replaced it with a new one.
Spark Plug: The spark plug was fouled with carbon buildup. I cleaned it with a wire brush and checked the gap.
Carburetor: I suspected the carburetor was the main culprit. I disassembled it and cleaned the jets and passages with carburetor cleaner and compressed air. The jets were indeed clogged with dried fuel residue.
Reassembly and Testing: After reassembling the carburetor, I tried to start the trimmer. It still wouldn’t start. I used the “burp” technique to clear the engine of excess fuel.
Starting Fluid: As a last resort, I sprayed a small amount of starting fluid into the carburetor intake. The trimmer sputtered to life!
Fine Tuning: Once the trimmer was running, I adjusted the idle speed and the high-speed mixture to ensure it was running smoothly.

The key to reviving this neglected trimmer was patience and a systematic approach. By checking each component and addressing the underlying problems, I was able to get it running like new.

Case Study 2: Solving Intermittent Starting Issues on a Stihl FS 90 R

A friend of mine was having trouble with his Stihl FS 90 R trimmer. It would start sometimes, but other times it would refuse to start. The problem was intermittent, which made it difficult to diagnose.

Initial Checks: We started by checking the fuel, spark, and air. All seemed to be in good order.
Fuel Cap Vent: We suspected the fuel cap vent might be clogged. We loosened the fuel cap slightly and tried to start the trimmer. It started right away!
Fuel Cap Replacement: We replaced the fuel cap with a new one. The problem was solved.

This case study highlights the importance of checking the simple things first. A clogged fuel cap vent can be a sneaky cause of starting problems.

Wood Type Considerations for Trimmer Use

The type of wood you’re clearing around can also impact the demands on your trimmer. For example, clearing around hardwoods like oak or maple, often found in firewood lots, requires a more robust trimmer head and potentially a higher power engine. Softwoods like pine or spruce are generally easier to clear.

Hardwoods: Dense and tough, requiring more power to cut through.
Softwoods: Easier to cut, but can be resinous and sticky, potentially clogging trimmer heads.
Brush and Undergrowth: A mix of grasses, weeds, and small shrubs.

Understanding the type of vegetation you’re dealing with will help you choose the right trimmer and cutting head for the job. I often switch between a string head for general clearing and a blade attachment for tougher brush.

Safety First: Essential Gear and Practices

Before you start troubleshooting your trimmer, it’s crucial to prioritize safety.

Eye Protection: Wear safety glasses or a face shield to protect your eyes from flying debris.
Hearing Protection: Trimmers can be loud. Wear earplugs or earmuffs to protect your hearing.
Gloves: Wear gloves to protect your hands from cuts and abrasions.
Long Pants and Closed-Toe Shoes: Protect your legs and feet from flying debris.
Read the Manual: Familiarize yourself with the manufacturer’s instructions and safety precautions.
Work in a Well-Ventilated Area: When working with gasoline and carburetor cleaner, work in a well-ventilated area to avoid inhaling harmful fumes.
Disconnect the Spark Plug: Before performing any maintenance on the trimmer, disconnect the spark plug wire to prevent accidental starting.

Strategic Insights for Wood Processing and Firewood Preparation

A reliable trimmer is a key component in efficient wood processing and firewood preparation. Here are some strategic insights:

Clearing Access Paths: Use a trimmer to clear paths to timber stands and firewood piles, making it easier to transport materials.
Brush Control: Keep brush and undergrowth under control around logging sites to reduce the risk of fire and improve visibility.
Firewood Storage: Clear the area around your firewood stacks to improve air circulation and reduce the risk of pests and diseases. I’ve found that a well-maintained clearing can significantly reduce wood rot.
Trail Maintenance: Maintain trails for accessing firewood lots and timber stands. A well-maintained trail makes it easier to transport equipment and materials.
Landscaping: Use a trimmer to keep your yard tidy and free of weeds. A well-maintained yard improves the overall aesthetic of your property.

Costs and Considerations for DIY vs. Professional Repair

Deciding whether to tackle a trimmer repair yourself or take it to a professional depends on your skill level, the complexity of the problem, and the cost of parts and labor.

DIY Repair:
- Pros: Lower cost (parts only), learning experience, convenience.
- Cons: Time-consuming, potential for mistakes, may require specialized tools.
- Typical Costs: Spark plug ($5-$10), air filter ($10-$20), fuel filter ($5-$10), carburetor rebuild kit ($20-$40).
Professional Repair:
- Pros: Expertise, guaranteed work, saves time.
- Cons: Higher cost (labor and parts), inconvenience.
- Typical Costs: Labor ($50-$100 per hour), carburetor replacement ($100-$200).

If the problem is simple, such as a dirty air filter or a fouled spark plug, a DIY repair is usually the best option. However, if the problem is more complex, such as a carburetor issue or an ignition problem, it may be best to take the trimmer to a professional. In my experience, a good rule of thumb is if you’re unsure, consult a professional.

Drying Methods and Moisture Content Targets for Firewood

While not directly related to the trimmer itself, understanding firewood drying is essential for anyone involved in firewood preparation. A trimmer is often used to clear the area around firewood stacks, so it’s important to understand the process.

Green Wood: Freshly cut wood with a high moisture content (50% or more).
Seasoned Wood: Wood that has been dried to a lower moisture content (20% or less). Seasoned wood burns more efficiently and produces less smoke.
Air Drying: The most common method of drying firewood. Stack the wood in a sunny, well-ventilated area and allow it to dry for 6-12 months. I personally prefer stacking wood in long, narrow rows to maximize air exposure.
Kiln Drying: A faster method of drying firewood. Wood is placed in a kiln and heated to a high temperature, which removes the moisture. Kiln-dried firewood is typically ready to burn in a few days.
Moisture Content Targets: For optimal burning, firewood should have a moisture content of 20% or less. You can use a moisture meter to measure the moisture content of the wood.

Next Steps: Implementing Your Knowledge

Now that you’ve learned about troubleshooting and repairing Stihl trimmers, it’s time to put your knowledge into practice.

Assess Your Trimmer: If your trimmer isn’t starting, follow the troubleshooting steps outlined in this guide.
Gather Your Tools: Make sure you have the necessary tools and supplies, such as a screwdriver, a spark plug wrench, carburetor cleaner, and a new spark plug.
Start with the Basics: Check the fuel, spark, and air first. These are the most common causes of starting problems.
Don’t Be Afraid to Ask for Help: If you’re not comfortable working on small engines, don’t hesitate to take your trimmer to a professional.
Maintain Your Trimmer: Regular maintenance, such as cleaning the air filter and changing the spark plug, can help prevent starting problems in the future.
Practice Safety: Always wear safety glasses, hearing protection, and gloves when working on your trimmer.

By following these steps, you can keep your Stihl trimmer running smoothly and efficiently, ensuring that you’re always ready to tackle your wood processing and firewood preparation tasks.

Final Thoughts

A non-starting Stihl trimmer can be a major inconvenience, but with a little knowledge and patience, you can often diagnose and fix the problem yourself. Remember to start with the basics, check the fuel, spark, and air, and don’t be afraid to get your hands dirty. By following the steps outlined in this guide, you can keep your trimmer running smoothly and efficiently, ensuring that you’re always ready to tackle your wood processing and firewood preparation tasks. And remember, safety should always be your top priority.