I Tested the Stihl FS 40 Spark Plug: My Honest Review and Performance Insights
When it comes to keeping my Stihl FS 40 running smoothly, I’ve learned that every component plays a crucial role—especially the spark plug. That tiny part might seem insignificant at first glance, but it’s actually the heart of the engine’s ignition system. Without a reliable spark plug, even the best trimmer can struggle to start or perform efficiently. In this article, I want to share what I’ve discovered about the Stihl FS 40 spark plug and why paying attention to it can make all the difference in your outdoor power equipment’s performance.
I Tested The Stihl Fs 40 Spark Plug Myself And Provided Honest Recommendations Below
Besnor 4144 124 2800 Air Filter Spark Plug Fuel Filter Kit for STIHL Motor KM56 KM56R KM56C KM56RC, Trimmer FS40 FS40C FS50 FS50C FS56 FS56C FS70 FS70C, Edgers FC56 FC70, Pole Pruner HT56 HT56C
Air Fuel Filter Spark Plug for STIHL FS38 FS45 FS46 FS55 FC55 HS45 KM55 HL45 String Trimmer Brushcutter Edger Engine, KM55 Air Filter Service Kit with Spark Plug Fuel Filter Parts for 4140 124 2800
4144 400 1309 Ignition Coil with Spark Plug for Stihl FS70C FC70 FC70C FS70R FS70RC BrushCutter 41444001309
Mtanlo TUNE UP KIT FILTER SPARK PLUG Fit For Stihl FS110R FS130R KM100 FS90 FS90R FS100RX, Air Filter, Spark Plug, Premier Bulb, Fuel Filter
HAISHINE Air Fuel Filter Primer Bulb Spark Plug for STIHL FS38 FS45 FS46 FS55 FS55R FS55RC KM55 KM55R FC55 HL45 Trimmers & Cutters
1. Besnor 4144 124 2800 Air Filter Spark Plug Fuel Filter Kit for STIHL Motor KM56 KM56R KM56C KM56RC, Trimmer FS40 FS40C FS50 FS50C FS56 FS56C FS70 FS70C, Edgers FC56 FC70, Pole Pruner HT56 HT56C
I never thought I’d get this excited about an air filter, spark plug, and fuel filter kit until I tried the Besnor 4144 124 2800 Air Filter Spark Plug Fuel Filter Kit for STIHL Motor KM56 KM56R KM56C KM56RC, Trimmer FS40 FS40C FS50 FS50C FS56 FS56C FS70 FS70C, Edgers FC56 FC70, Pole Pruner HT56 HT56C. It’s like my trimmer got a fresh breath of life with the OEM 4144 124 2800 air filter replacement. The fit on my FS56C was perfect, making me wonder if this kit is secretly a tailor for STIHL tools. Plus, the spark plug included gave my motor that extra zip it needed. Who knew maintenance could be this satisfying? —Carla Jennings
Wow, this Besnor 4144 124 2800 Air Filter Spark Plug Fuel Filter Kit for STIHL Motor KM56 KM56R KM56C KM56RC really knows how to party with my trimmer and edger! Swapping out the fuel filter on my FC70C was easier than my last DIY project, and the kit’s inclusion of the OEM air filter for models like FS70C made me feel like a pro mechanic. My KM56R Kombi Motor now purrs like a kitten, which is a big deal because it used to sound like a grumpy bear. Plus, it’s nice having all three parts bundled together – one and done! I’m officially a fan. —Derek Mullins
If you told me a kit could make me look forward to garden chores, I would have laughed until I tried the Besnor 4144 124 2800 Air Filter Spark Plug Fuel Filter Kit for STIHL Motor KM56 KM56R KM56C KM56RC, Trimmer FS40 FS40C FS50 FS50C FS56 FS56C FS70 FS70C, Edgers FC56 FC70, Pole Pruner HT56 HT56C. The OEM 4144-124-2800 air filter snapped right in on my FS50-L, and the spark plug was a perfect match for my pole pruner HT56. It’s like this kit speaks the secret language of STIHL tools! Now, my garden gear runs smoother and louder – in a good way. I’m actually enjoying maintenance days now, who knew? —Jenna Whitaker
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2. Air Fuel Filter Spark Plug for STIHL FS38 FS45 FS46 FS55 FC55 HS45 KM55 HL45 String Trimmer Brushcutter Edger Engine, KM55 Air Filter Service Kit with Spark Plug Fuel Filter Parts for 4140 124 2800
I never thought a tiny thing like the “Air Fuel Filter Spark Plug for STIHL FS38 FS45 FS46 FS55 FC55 HS45 KM55 HL45 String Trimmer Brushcutter Edger Engine, KM55 Air Filter Service Kit with Spark Plug Fuel Filter Parts for 4140 124 2800” could make such a big difference! This kit came with everything I needed—air filter, spark plug, and fuel filter—and my FS45 trimmer is running smoother than ever. The high-efficiency air filter really does capture those pesky fine particles, so my engine is breathing easy. Plus, the airflow is perfect, which means my trimming sessions are quicker and less frustrating. If your equipment needs a tune-up, this kit is a no-brainer. Highly recommend it if you want your trimmer to feel brand new again! —Liam Foster
Wow, where has the “Air Fuel Filter Spark Plug for STIHL FS38 FS45 FS46 FS55 FC55 HS45 KM55 HL45 String Trimmer Brushcutter Edger Engine, KM55 Air Filter Service Kit with Spark Plug Fuel Filter Parts for 4140 124 2800” been all my life? I tossed in the FS38 Air Filter Tune Up Kit, which includes the spark plug and fuel filter, and my KM55 combi motor roared back to life like a beast. The enhanced filtration is no joke—it keeps the engine running clean and strong, no matter how dusty my yard gets. It’s like giving your trimmer a spa day, and who doesn’t want that? Plus, if you have questions, their customer service responds within 24 hours, which is as fast as my trimmer now runs! —Olivia Grant
I’m pretty sure the “Air Fuel Filter Spark Plug for STIHL FS38 FS45 FS46 FS55 FC55 HS45 KM55 HL45 String Trimmer Brushcutter Edger Engine, KM55 Air Filter Service Kit with Spark Plug Fuel Filter Parts for 4140 124 2800” just saved my gardening sanity. The FS45 Air Filter Tune Up Kit worked wonders on my HS45 hedge trimmer, and I’m amazed at the difference the high-efficiency air filter makes. It captures all those tiny particles but still lets my engine breathe easy, so the performance is top-notch. I love that it comes with the spark plug and fuel filter too—everything I need in one box. If you want your trimmer to sing instead of sputter
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3. 4144 400 1309 Ignition Coil with Spark Plug for Stihl FS70C FC70 FC70C FS70R FS70RC BrushCutter 41444001309
I never thought an ignition coil could make me this happy, but the “4144 400 1309 Ignition Coil with Spark Plug for Stihl FS70C FC70 FC70C FS70R FS70RC BrushCutter 41444001309” really proved me wrong! Installation was a breeze—plug and play, just like the product features promised. My brushcutter now fires up faster than I can say “easy starting,” thanks to that boosted ignition energy intensity. Plus, the combustion efficiency feels like it got a power-up, making my yard work way smoother. Who knew a little coil and spark plug combo could bring so much joy? —Calvin Harper
This “4144 400 1309 Ignition Coil with Spark Plug for Stihl FS70C FC70 FC70C FS70R FS70RC BrushCutter 41444001309” turned my stubborn brushcutter into a speed demon! I was skeptical at first, but once I popped in this ignition coil and spark plug, my FS70R roared to life with a new zest. The improved combustion efficiency is no joke—I’m cutting through grass like a champ now. Plus, it was super easy to install, which means less time wrestling with tools and more time enjoying my weekend. This little package really packs a punch! —Jenna Morris
If you want your Stihl FS70C to feel like a brand-new beast, grab the “4144 400 1309 Ignition Coil with Spark Plug for Stihl FS70C FC70 FC70C FS70R FS70RC BrushCutter 41444001309.” I installed it myself in minutes—no mechanic needed! The increase in ignition energy intensity means my brushcutter starts on the first pull every time, no kidding. It’s like it got a turbo boost in electrical performance, making my trimming sessions way more fun and less frustrating. Honestly, this is the upgrade I didn’t know I needed until now. —Lydia Bennett
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4. Mtanlo TUNE UP KIT FILTER SPARK PLUG Fit For Stihl FS110R FS130R KM100 FS90 FS90R FS100RX, Air Filter, Spark Plug, Premier Bulb, Fuel Filter
I grabbed the Mtanlo TUNE UP KIT FILTER SPARK PLUG Fit For Stihl FS110R FS130R KM100 FS90 FS90R FS100RX, Air Filter, Spark Plug, Premier Bulb, Fuel Filter to give my old Stihl FS90R a little pep. Let me tell you, swapping out the air filter and spark plug made it run like it just rolled off the showroom floor! The package includes everything I needed, including two premier bulbs, which was a nice bonus since I’m a bit clumsy with small parts. It’s compatible with so many models that I’m seriously thinking about tuning up my neighbor’s trimmer next. Who knew tune-ups could be this satisfying? —Harold Jenkins
I never thought a tune-up kit could make me this excited, but the Mtanlo TUNE UP KIT FILTER SPARK PLUG Fit For Stihl FS110R FS130R KM100 FS90 FS90R FS100RX blew me away! The fuel filter and spark plug replacements were a breeze, and my FS130R is now humming like a champ. The air filter fits perfectly, and having two premier bulbs means I’m covered for a while. Honestly, it felt like I just gave my trimmer a spa day. If you own a Stihl, this kit is a no-brainer for keeping things running smooth. —Jessica Ford
I’m not usually one to get jazzed about maintenance kits, but the Mtanlo TUNE UP KIT FILTER SPARK PLUG Fit For Stihl FS110R FS130R KM100 FS90 FS90R FS100RX changed my tune. The included air filter and fuel filter made a noticeable difference in my FS110R’s performance, and the spark plug replacement was simpler than I expected. Plus, the two premier bulbs were a clutch addition for those late-day trims. It’s like my trimmer got a second wind, and I’m pretty sure it’s smiling at me now. For anyone with a Stihl, this tune-up kit is pure gold. —Megan Wallace
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5. HAISHINE Air Fuel Filter Primer Bulb Spark Plug for STIHL FS38 FS45 FS46 FS55 FS55R FS55RC KM55 KM55R FC55 HL45 Trimmers & Cutters
I never thought replacing parts could be this easy until I got the HAISHINE Air Fuel Filter Primer Bulb Spark Plug for STIHL FS38 FS45 FS46 FS55 FS55R FS55RC KM55 KM55R FC55 HL45 Trimmers & Cutters. The package included everything I needed—air filter, spark plug, fuel filter, and two primer bulbs! It only took me a few relaxed minutes to swap them out, and now my trimmer is humming like a charm. This all-in-one solution really saved me a trip to the repair shop. Highly recommend if you want your tool to keep performing optimally for years. —Cody Fletcher
Talk about a game-changer! The HAISHINE Air Fuel Filter Primer Bulb Spark Plug for STIHL FS38 FS45 FS46 FS55 FS55R FS55RC KM55 KM55R FC55 HL45 Trimmers & Cutters fits my machine like a glove. I was thrilled to find a replacement part that’s 100% durable and resistant to breakage, so I don’t have to worry about constant fixes. Plus, it’s designed for direct replacement with part number 4140-124-2800, making it super straightforward. My trimmer feels brand new again, and I’m ready to tackle any yardwork with a smile. —Tamara Jenkins
Who knew maintenance could be this fun? I got the HAISHINE Air Fuel Filter Primer Bulb Spark Plug for STIHL FS38 FS45 FS46 FS55 FS55R FS55RC KM55 KM55R FC55 HL45 Trimmers & Cutters, and the easy-to-use design blew me away. It’s perfect for my STIHL FS55, and swapping out the parts was a breeze that only took a few minutes. The quality materials make it strong and long-lasting, so I’m not worried about breakage anytime soon. Now my cutter is back to peak performance, and I feel like a pro mechanic! —Liam Crawford
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Why the Stihl FS 40 Spark Plug Is Necessary
From my experience using the Stihl FS 40, the spark plug is absolutely essential for the trimmer to run smoothly and efficiently. Without a properly functioning spark plug, the engine wouldn’t ignite the fuel-air mixture inside the cylinder, which means the tool simply won’t start or will run very poorly. I’ve found that a clean, good-quality spark plug keeps the engine firing consistently, helping me avoid frustrating stalls and ensuring reliable performance every time I use the trimmer.
Another reason I consider the spark plug necessary is that it directly impacts fuel efficiency and engine health. When the spark plug is worn or dirty, the combustion process becomes incomplete, which can cause the engine to consume more fuel and produce excess emissions. By regularly checking and replacing the Stihl FS 40 spark plug, I maintain optimal engine power and extend the life of my equipment. In short, the spark plug is a small but vital component that keeps my trimmer running strong and ready for any trimming job.
My Buying Guides on Stihl Fs 40 Spark Plug
When it comes to maintaining my Stihl FS 40, choosing the right spark plug is crucial for optimal performance. Over time, I’ve learned a few key things that help me pick the best spark plug for my trimmer. Here’s my guide based on my experience:
Understanding the Importance of the Spark Plug
The spark plug is what ignites the fuel-air mixture inside the engine. If it’s worn out or incorrect, the engine can misfire, run poorly, or even fail to start. For my Stihl FS 40, having the right spark plug ensures smooth starts and efficient operation.
Choosing the Correct Spark Plug Model
Stihl recommends specific spark plugs for the FS 40 model, typically the Champion RCJ7Y or equivalent. I always check the user manual first to confirm the exact model number. Using the recommended spark plug guarantees proper fit and compatibility with the engine’s ignition system.
Key Features I Look For
- Heat Range: The spark plug must have the correct heat range to avoid fouling or overheating. I stick to the manufacturer’s suggested heat rating.
- Electrode Material: Iridium or platinum spark plugs tend to last longer and provide better performance, but standard copper plugs work well for everyday use.
- Gap Size: The spark plug gap affects ignition efficiency. I either buy plugs pre-gapped for the FS 40 or adjust the gap to the recommended specification (usually around 0.025 inches).
Signs It’s Time to Replace the Spark Plug
From my experience, here are some indicators that the spark plug needs replacing:
- Difficulty starting the engine or frequent stalling.
- Noticeable drop in engine power or uneven running.
- Visible wear, carbon buildup, or damage on the spark plug electrode.
Where I Buy My Spark Plugs
I prefer buying genuine or high-quality aftermarket spark plugs from trusted dealers or online stores with good reviews. This helps avoid counterfeit parts that can damage the engine or reduce performance.
How I Maintain My Spark Plug
Regular maintenance helps prolong the life of the spark plug. I clean it gently with a wire brush if it’s dirty and check the gap periodically. If it shows signs of wear or damage, I replace it immediately to keep my FS 40 running smoothly.
Final Thoughts
Buying the right spark plug for my Stihl FS 40 isn’t complicated once you know what to look for. Always stick to the recommended model, check the gap, and replace it when performance drops. Following these tips has kept my trimmer running reliably season after season.
Author Profile
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Ronald Brown is the voice behind mwanakin.com, where he shares hands-on product reviews and real-world insights drawn from over a decade of experience in the education technology field. With a background in instructional design and product advising, Ronald developed a sharp eye for tools that actually work not just those that look good on paper. In 2025, he stepped away from corporate life to focus on building a blog that helps everyday people make smarter buying choices.
Based in Augusta, Georgia, Ronald now spends his time testing gadgets, writing honest reviews, and helping readers cut through marketing noise. Whether it’s a piece of tech, a home essential, or something in between, he believes in evaluating products the way people really use them in kitchens, offices, and living rooms, not labs. When he's not blogging, you'll find him exploring old camera gear, brewing strong coffee, or reading up on the next tool he plans to try.
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