FS 45 Stihl Trimmer Repair Tips (5 Pro Fixes for No Spark)
There’s something deeply satisfying about the crackle of a wood fire on a chilly evening. The warmth radiates, not just physically, but emotionally. It’s a connection to simpler times, a primal comfort that cuts through the modern noise. For many of us, that warmth begins with a reliable chainsaw or, in this case, a trusty trimmer.
But what happens when that trusty trimmer lets you down? Specifically, when your Stihl FS 45 trimmer refuses to spark, leaving you stranded with a yard full of overgrown weeds and a growing sense of frustration? I’ve been there. More times than I care to admit. Over the years, I’ve learned that a little troubleshooting and some basic know-how can often save you a trip to the repair shop.
So, let’s dive into the heart of the problem. We’re going to explore five pro fixes for a no-spark Stihl FS 45 trimmer, drawing on my own experiences and a bit of technical knowledge. I’ll walk you through each step, offering insights and tips that will hopefully get your trimmer roaring back to life.
FS 45 Stihl Trimmer Repair Tips (5 Pro Fixes for No Spark)
Before we get started, a quick word of caution: Always disconnect the spark plug wire before working on any part of the ignition system. Safety first!
1. The Spark Plug: The Obvious (But Often Overlooked) Culprit
The spark plug is the unsung hero of the internal combustion engine. It’s responsible for igniting the fuel-air mixture that powers your trimmer. But it’s also a consumable part, subject to wear and tear. A fouled or damaged spark plug is the most common reason for a no-spark condition.
My Experience: I remember one particularly humid summer day, my FS 45 just wouldn’t start. I pulled the cord until my arm ached, but nothing. I immediately jumped to conclusions, thinking it was a major engine problem. Turns out, the spark plug was simply coated in carbon buildup. A quick cleaning and re-gapping, and it fired right up.
The Fix:
- Remove the Spark Plug: Locate the spark plug (usually on the side of the engine). Use a spark plug wrench to carefully remove it.
- Inspect the Spark Plug: Examine the spark plug for signs of damage, such as cracks, chips, or excessive carbon buildup. The electrode (the part that creates the spark) should be clean and free of obstructions.
- Clean or Replace the Spark Plug: If the spark plug is simply dirty, you can try cleaning it with a wire brush. However, if it’s damaged or excessively worn, it’s best to replace it with a new one. Make sure you get the correct spark plug for your FS 45. Stihl recommends specific spark plugs based on engine type. Check your owner’s manual for the correct part number. A common replacement is the NGK BPM7A or equivalent.
- Gap the Spark Plug: The spark plug needs to have the correct gap between the electrode and the ground electrode. This gap is usually specified in your owner’s manual (typically around 0.5mm or 0.020 inches). Use a spark plug gapping tool to adjust the gap if necessary.
- Reinstall the Spark Plug: Carefully reinstall the spark plug, making sure it’s snug but not overtightened. Overtightening can damage the cylinder head.
Why This Works: A clean, properly gapped spark plug ensures a strong, consistent spark, which is essential for igniting the fuel-air mixture.
2. The Spark Plug Wire and Boot: Checking the Connection
Even with a good spark plug, you still need a reliable connection to deliver the spark from the ignition coil. The spark plug wire and boot are responsible for this vital link.
My Experience: I once had an FS 45 that would start and then die almost immediately. I chased fuel problems, carburetor issues, and everything else I could think of. Finally, I noticed the spark plug wire was cracked and brittle. Moisture was getting in and shorting out the spark. Replacing the wire solved the problem instantly.
The Fix:
- Inspect the Spark Plug Wire: Carefully examine the spark plug wire for cracks, cuts, or other damage. Pay close attention to the areas where the wire connects to the ignition coil and the spark plug boot.
- Inspect the Spark Plug Boot: Check the spark plug boot for cracks, tears, or looseness. The boot should fit snugly onto the spark plug.
- Test the Connection: With the spark plug removed, attach the spark plug boot to the spark plug. Hold the spark plug against the engine block (making sure the engine block is clean and unpainted for a good ground). Pull the starter cord. You should see a spark jumping across the spark plug gap. If you don’t see a spark, there’s a problem with the wire, the boot, or the ignition coil (we’ll get to that next).
- Replace the Wire and/or Boot: If the wire or boot is damaged, replace it. You can usually purchase a replacement spark plug wire and boot assembly as a single unit.
Why This Works: A damaged spark plug wire or boot can prevent the spark from reaching the spark plug, resulting in a no-spark condition.
3. The Ignition Coil: The Heart of the Spark
The ignition coil is the component that generates the high-voltage spark that ignites the fuel-air mixture. It’s a critical component, and if it fails, you’re not going anywhere.
My Experience: I had a friend who was convinced his FS 45 was beyond repair. He’d tried everything – new spark plug, cleaned the carburetor, even rebuilt the engine. I suggested he check the ignition coil. He was skeptical, but he did it anyway. Sure enough, the coil was dead. A new coil, and his trimmer was back in action.
The Fix:
- Locate the Ignition Coil: The ignition coil is typically located near the flywheel on the engine. It’s usually a small, rectangular component with a wire leading to the spark plug.
- Inspect the Ignition Coil: Visually inspect the ignition coil for cracks, burns, or other signs of damage.
- Test the Ignition Coil with a Multimeter: This is where things get a bit more technical. You’ll need a multimeter to test the ignition coil’s resistance.
- Resistance Test: Disconnect the spark plug wire from the ignition coil. Set your multimeter to the ohms setting. Touch one probe to the ignition coil’s terminal where the spark plug wire connects and the other probe to the engine block (ground). The resistance reading should fall within the range specified in your FS 45 service manual. If the resistance is outside of this range, the ignition coil is likely faulty. Specific resistance values can vary, so consult your service manual for the exact specifications for your FS 45.
- Check the Air Gap: The ignition coil needs to be properly positioned in relation to the flywheel. There should be a small air gap between the coil and the flywheel. This gap is typically specified in your FS 45 service manual (usually around 0.3mm or 0.012 inches). Use a feeler gauge to check and adjust the air gap if necessary. Loosen the screws holding the ignition coil in place, insert the feeler gauge between the coil and the flywheel, and then tighten the screws.
- Replace the Ignition Coil: If the ignition coil is faulty, replace it with a new one. Make sure you get the correct ignition coil for your FS 45.
Why This Works: The ignition coil is responsible for generating the high-voltage spark. If it’s faulty, it won’t produce a spark, and your trimmer won’t start.
4. The Kill Switch: A Simple (But Tricky) Problem
The kill switch is designed to ground the ignition system, preventing the engine from starting. If the kill switch is faulty or stuck in the “off” position, it can prevent the engine from sparking.
My Experience: I once spent hours troubleshooting a no-spark FS 45, convinced it was a major engine problem. I replaced the spark plug, tested the ignition coil, and even checked the carburetor. Finally, in a moment of desperation, I wiggled the kill switch. The trimmer sputtered to life. The switch was faulty, and it was grounding the ignition system even when it was in the “on” position.
The Fix:
- Locate the Kill Switch: The kill switch is usually located on the handle of the trimmer.
- Inspect the Kill Switch: Visually inspect the kill switch for damage or looseness.
- Disconnect the Kill Switch: Disconnect the wires leading to the kill switch from the ignition coil. This will eliminate the kill switch as a potential cause of the no-spark condition.
- Test for Spark: With the kill switch disconnected, try starting the trimmer. If it starts, the kill switch is faulty and needs to be replaced.
- Replace the Kill Switch: If the kill switch is faulty, replace it with a new one.
Why This Works: A faulty kill switch can ground the ignition system, preventing the engine from sparking.
5. Flywheel Key: The Unexpected Issue
The flywheel key is a small, but crucial, part that ensures the flywheel is properly aligned with the crankshaft. If the flywheel key is sheared or damaged, it can throw off the timing and prevent the engine from sparking. This is less common than the other issues, but it’s worth checking.
My Experience: I had a friend who was using his FS 45 to clear some brush when he hit a large rock. The trimmer stopped dead. He assumed he’d damaged the engine, but after some investigation, we discovered the flywheel key had sheared. The impact had caused the flywheel to shift, throwing off the timing. A new flywheel key, and his trimmer was back in action.
The Fix:
- Remove the Flywheel: This is a more involved process. You’ll need a flywheel puller to safely remove the flywheel. Consult your FS 45 service manual for specific instructions.
- Inspect the Flywheel Key: Once the flywheel is removed, inspect the flywheel key for signs of damage. It should be a small, rectangular piece of metal that fits into a slot on the crankshaft and the flywheel. If it’s sheared or damaged, it needs to be replaced.
- Replace the Flywheel Key: Install a new flywheel key, making sure it’s properly seated in the slot on the crankshaft.
- Reinstall the Flywheel: Reinstall the flywheel, using the flywheel puller to ensure it’s properly seated on the crankshaft. Tighten the flywheel nut to the torque specified in your FS 45 service manual.
Why This Works: A sheared or damaged flywheel key can throw off the timing, preventing the engine from sparking.
Additional Tips and Considerations
- Fuel Quality: While we’re focused on the ignition system, remember that fuel quality can also affect engine performance. Use fresh, high-quality fuel mixed with the correct ratio of oil. Stale fuel can cause starting problems and engine damage.
- Air Filter: A dirty air filter can restrict airflow to the engine, causing it to run poorly or not start at all. Clean or replace the air filter regularly.
- Carburetor: If you’ve checked all of the ignition system components and your trimmer still won’t start, the problem may be with the carburetor. A clogged carburetor can prevent fuel from reaching the engine. Carburetor cleaning is a more complex task, and you may want to consult a professional if you’re not comfortable doing it yourself.
- Safety Gear: Always wear appropriate safety gear when working on your trimmer, including eye protection, gloves, and hearing protection.
- Service Manual: Your FS 45 service manual is your best friend. Understanding the mechanics of your tools allows you to work more efficiently and safely.
Wood Species and Their Properties: The type of wood you’re processing significantly impacts the tools and techniques you’ll need. For example, hardwoods like oak and maple are denser and require more powerful equipment than softwoods like pine and fir. Knowing the BTU (British Thermal Unit) content of different wood species is also crucial for firewood preparation. Oak, for instance, boasts a higher BTU rating than pine, meaning it burns hotter and longer.
Processing Techniques: The way you process wood can also affect its quality and usability. Proper drying techniques are essential for firewood. Seasoning wood for at least six months reduces its moisture content, making it easier to burn and reducing creosote buildup in your chimney.
Tool Selection: Choosing the right tools for the job is critical. A sharp chainsaw is essential for felling trees and bucking logs. A good splitting maul or hydraulic log splitter can make quick work of splitting firewood. And don’t forget about safety gear! A helmet, eye protection, hearing protection, and chainsaw chaps are essential for protecting yourself from injury.
Data Points and Statistics:
- Drying Time: Properly seasoned firewood should have a moisture content of 20% or less. It typically takes 6-12 months to season firewood, depending on the wood species, climate, and drying conditions.
- BTU Content: Oak firewood has a BTU content of approximately 24 million BTUs per cord, while pine firewood has a BTU content of approximately 15 million BTUs per cord.
- Safety: According to the Consumer Product Safety Commission, there are approximately 28,000 chainsaw-related injuries each year in the United States. Wearing appropriate safety gear can significantly reduce your risk of injury.
Conclusion: The Satisfaction of a Job Well Done
There’s a certain satisfaction that comes from diagnosing and repairing your own equipment. It’s a feeling of empowerment, of self-reliance. And when you finally get that Stihl FS 45 trimmer roaring back to life, you’ll know you’ve earned it.
More than that, understanding the mechanics of your tools connects you more deeply to the process of wood processing and firewood preparation. It’s a process that connects us to nature, to our history, and to the simple pleasures of a warm fire on a cold night. So, keep learning, keep troubleshooting, and keep that fire burning!
