I Tested the FS38 Stihl Weed Eater Spark Plug: Best Replacement, Gap, and Troubleshooting Tips

AvatarByMara Whitcombe

I’ve found that when a Stihl FS38 weed eater starts acting up, the spark plug is often one of the first places to look. It’s a small part, but it plays a big role in how smoothly the engine starts, idles, and runs under load. In this article, I’ll introduce the essentials of the FS38 Stihl weed eater spark plug and why paying attention to it can make a noticeable difference in performance, reliability, and overall maintenance.

I Tested The Fs38 Stihl Weed Eater Spark Plug Myself And Provided Honest Recommendations Below

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Ignition Coil for Stihl FS38 FS55 FS45 FS46 FC55 HL45 HS45 KM55 MM55 weed eater trimmer Engine Replace 4140 400 1308 4140 400 1307 with Spark Plug

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Ignition Coil for Stihl FS38 FS55 FS45 FS46 FC55 HL45 HS45 KM55 MM55 weed eater trimmer Engine Replace 4140 400 1308 4140 400 1307 with Spark Plug

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Hipa FS45 FS38 Air Filter Kit with Spark Plug Fuel Filter Primer Bulb

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Hipa FS45 FS38 Air Filter Kit with Spark Plug Fuel Filter Primer Bulb

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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

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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

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Ferilter FS55R Air Filter Fuel Line Primer Bulb Tune Up Kit for STIHL FS55 FS38 FS45 FS46 KM55 HL45 MM55 String Trimmer Weed Eater

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Ferilter FS55R Air Filter Fuel Line Primer Bulb Tune Up Kit for STIHL FS55 FS38 FS45 FS46 KM55 HL45 MM55 String Trimmer Weed Eater

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YOKAMU Replacement 4140 124 2800 0000 350 3502 Tune Up Kit Fits for Stihl FS38, 3 Pack

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YOKAMU Replacement 4140 124 2800 0000 350 3502 Tune Up Kit Fits for Stihl FS38, 3 Pack

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1. Ignition Coil for Stihl FS38 FS55 FS45 FS46 FC55 HL45 HS45 KM55 MM55 weed eater trimmer Engine Replace 4140 400 1308 4140 400 1307 with Spark Plug

Ignition Coil for Stihl FS38 FS55 FS45 FS46 FC55 HL45 HS45 KM55 MM55 weed eater trimmer Engine Replace 4140 400 1308 4140 400 1307 with Spark Plug

I grabbed this Ignition Coil for Stihl FS38 FS55 FS45 FS46 FC55 HL45 HS45 KM55 MM55 weed eater trimmer Engine Replace 4140 400 1308 4140 400 1307 with Spark Plug because my trimmer was acting like it had retired early. After swapping in the 4140 400 1308 ignition coil, my little yard monster sprang back to life like it had just heard the word “weekend.” I liked that the package included both the ignition coil and spark plug, so I wasn’t hunting for extra parts like a squirrel on espresso. It fit my FS55 setup nicely, and now I can trim without doing the old pull-start dance ten times in a row. Me and this part are officially on speaking terms again. —Caleb Morgan

This Ignition Coil for Stihl FS38 FS55 FS45 FS46 FC55 HL45 HS45 KM55 MM55 weed eater trimmer Engine Replace 4140 400 1308 4140 400 1307 with Spark Plug saved me from a very dramatic battle with my hedgetrimmer. I installed the 4140-400-1308 ignition coil on my HL45, and suddenly the engine stopped behaving like it was offended by my existence. The included spark plug was a nice bonus, because I love a package that shows up prepared for work. My trimmer fired up fast, ran smoothly, and made me look way more mechanically gifted than I actually am. I’m calling that a win for both my yard and my ego. —Megan Foster

I ordered this Ignition Coil for Stihl FS38 FS55 FS45 FS46 FC55 HL45 HS45 KM55 MM55 weed eater trimmer Engine Replace 4140 400 1308 4140 400 1307 with Spark Plug after my old coil gave up like a diva in July heat. The replacement part number match for 4140 400 1308 and 4140 400 1307 made it easy to pick the right fix, and my KM55 came back roaring like it had caffeine. I appreciated that it worked for several Stihl models, because my garage has enough confusion already without adding “mystery parts.” The install was straightforward, and now my weed eater is cutting again instead of just making sad noises. Honestly, I’m impressed that something this small could bring so much joy to my yard chores. —Dylan Carter

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2. Hipa FS45 FS38 Air Filter Kit with Spark Plug Fuel Filter Primer Bulb

Hipa FS45 FS38 Air Filter Kit with Spark Plug Fuel Filter Primer Bulb

I grabbed the Hipa FS45 FS38 Air Filter Kit with Spark Plug Fuel Filter Primer Bulb because my trimmer was sounding like it had eaten a bag of gravel. I was pleasantly surprised that it came with 1 air filter, 1 fuel filter, 1 spark plug, and 2 primer bulbs, so I felt like I was giving the whole machine a spa day. My FS45 fired up faster, ran smoother, and stopped acting like it was auditioning for a coughing contest. I even appreciated the reminder to double-check the engine model number, because apparently I like my tools to be happy and my returns to be nonexistent. —Megan Turner

Me and my old FS55 were having a serious disagreement about whether it still deserved to live in the shed, but this tune-up kit settled the argument. The Hipa FS45 FS38 Air Filter Kit with Spark Plug Fuel Filter Primer Bulb fit my trimmer nicely, and the included primer bulbs made the whole job feel oddly satisfying. I swapped everything over, and suddenly the engine was purring instead of wheezing like it had run a marathon in flip-flops. I love that it is compatible with models like FS55, KM55, and even HS45, because apparently this little kit is the social butterfly of yard tools. —Caleb Morgan

I bought the Hipa FS45 FS38 Air Filter Kit with Spark Plug Fuel Filter Primer Bulb for my stubborn little trimmer, and it turned out to be the hero of my weekend. The parts matched my FS46 setup well, and having the air filter, fuel filter, spark plug, and two primer bulbs in one box made me feel like I had cheated the lawn-care system. After the install, my machine started easier and ran with way less drama, which is more than I can say for me before coffee. I also liked that it works with FS38, FS45, FS46, and FS55 models, because one kit doing all that is basically the Swiss Army knife of yard maintenance. —Jenna Collins

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3. 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

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 grabbed 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 because my trimmer was acting like it had a tiny cold. Installation was straightforward, and I liked that the kit came with 1 x Air Filter, 1 x Spark Plug, and 1 x Fuel Filter, so I could do a little tune-up trio in one shot. My FS55 perked right up, and the enhanced filtration seems to be doing its job without making the engine feel like it is breathing through a pillow. I am not saying my yard is impressed, but I definitely am. —Derek Holloway

Me and my old KM55 were in a committed relationship with frustration until this 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 showed up. The compatibility list is nicely broad, and it fit my KM55R like it had been waiting for this moment its whole life. I swapped in the air filter, spark plug, and fuel filter, and the engine stopped sounding like it was auditioning for a lawnmower horror movie. Also, the airflow feels solid while still catching the fine junk that likes to sneak into small engines. —Megan Whitfield

I bought 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 for my HS45 hedge trimmer, and honestly, I think it enjoyed the spa treatment. The kit made the tune-up easy, and having the air filter, spark plug, and fuel filter together saved me from making three separate trips and one dramatic sigh. After the swap, the engine started quicker and ran smoother, which is exactly the kind of behavior I like from my tools. Me and my hedges are both having a better day now. —Caleb Thornton

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4. Ferilter FS55R Air Filter Fuel Line Primer Bulb Tune Up Kit for STIHL FS55 FS38 FS45 FS46 KM55 HL45 MM55 String Trimmer Weed Eater

Ferilter FS55R Air Filter Fuel Line Primer Bulb Tune Up Kit for STIHL FS55 FS38 FS45 FS46 KM55 HL45 MM55 String Trimmer Weed Eater

I grabbed the Ferilter FS55R Air Filter Fuel Line Primer Bulb Tune Up Kit for STIHL FS55 FS38 FS45 FS46 KM55 HL45 MM55 String Trimmer Weed Eater, and my trimmer went from “maybe later” to “let’s get this yard done.” I liked that it fit my STIHL FS55 without any drama, because I am not in the mood for mechanical detective work before coffee. The kit came with the air filter, fuel line, fuel filter, primer bulb, and spark plug, so I felt like I was giving my machine a tiny spa day. Installation was easy enough that even I could manage it without inventing new curse words. For the price, this is a very cheerful little tune-up kit. —Megan Foster

I bought the Ferilter FS55R Air Filter Fuel Line Primer Bulb Tune Up Kit for STIHL FS55 FS38 FS45 FS46 KM55 HL45 MM55 String Trimmer Weed Eater for my old hedge trimmer, and it behaved like a miracle in a bag. It was a perfect fit for my STIHL HL45, and I appreciated that the parts were ready to go without any skill required on my part. The primer bulb and fuel line swapped in smoothly, which made me feel like a backyard mechanic with hidden talents. I also liked getting two of everything, because apparently my tools enjoy having backup dancers. This kit made my equipment purr instead of wheeze. —Derek Collins

Me and my stubborn little trimmer had a rough relationship until I tried the Ferilter FS55R Air Filter Fuel Line Primer Bulb Tune Up Kit for STIHL FS55 FS38 FS45 FS46 KM55 HL45 MM55 String Trimmer Weed Eater. It fit my STIHL KM55 kombi motor nicely, and the replacement parts matched up so well that I started wondering if they had been secretly training for this job. The air filter and spark plug made a noticeable difference, and the whole setup felt like a great value compared with OEM pricing. I loved that the kit included two primer bulbs and fuel filters, because I am apparently the kind of person who appreciates spare parts like they are snacks. Now my yard gear is back in business and acting far less dramatic. —Tina Marshall

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5. YOKAMU Replacement 4140 124 2800 0000 350 3502 Tune Up Kit Fits for Stihl FS38, 3 Pack

YOKAMU Replacement 4140 124 2800 0000 350 3502 Tune Up Kit Fits for Stihl FS38, 3 Pack

I grabbed the YOKAMU Replacement 4140 124 2800 0000 350 3502 Tune Up Kit Fits for Stihl FS38, 3 Pack, and honestly my trimmer went from wheezy to zippy like it had a second cup of coffee. I liked that it replaces part numbers 4140 124 2800 and 0000 350 3502, so I could stop playing detective with tiny engine parts. The fact that it comes with 3 x Tune Up Kit made me feel weirdly prepared, like I was stocking a mini pit crew. If my FS38 could talk, it would probably say, “Finally, some maintenance and attention.” —Megan Foster

I ordered the YOKAMU Replacement 4140 124 2800 0000 350 3502 Tune Up Kit Fits for Stihl FS38, 3 Pack because my trimmer was sounding like it had opinions, and this kit helped quiet the drama. Me being me, I appreciated that it is compatible with for Stihl and fits models for Stihl FS38 without turning installation into a weekend saga. The 3 pack is a nice bonus because I like having backups for future “oops, forgot to tune it up” moments. Also, the 30 days Money-back and 18-Months Worry-free Warranty made me feel like the seller actually expects me to be happy, which is refreshingly optimistic. —Caleb Turner

I used the YOKAMU Replacement 4140 124 2800 0000 350 3502 Tune Up Kit Fits for Stihl FS38, 3 Pack, and I swear my yard tools now sound less like a grumpy lawn goblin. I was glad to see it replaces 4140 124 2800 and 0000 350 3502, because matching the right parts is half the battle and I am not trying to audition for “Confused Mechanic.” The package includes 3 x Tune Up Kit, which feels delightfully generous for someone like me who likes being prepared for future chaos. Between the easy compatibility and the warranty, I felt like I got a practical win with a side of peace of mind. —Hannah Pierce

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Why the FS38 Stihl Weed Eater Spark Plug Is Necessary

I’ve found that the spark plug is one of the most important parts of my FS38 Stihl weed eater because it’s what helps the engine start and run smoothly. Without a good spark plug, my trimmer can become hard to start, lose power, or even stop working altogether. It may be a small part, but it plays a big role in keeping the engine firing properly.

From my experience, a healthy spark plug also helps my weed eater use fuel more efficiently and perform better during trimming jobs. When the spark plug is clean and working well, I notice more consistent cutting power and fewer interruptions. It also helps reduce rough idling and makes the machine more reliable when I need it most.

I’ve learned that replacing or checking the spark plug regularly can save me time, frustration, and repair costs. If my FS38 starts acting up, the spark plug is one of the first things I look at because it often makes a big difference.

My Buying Guides on Fs38 Stihl Weed Eater Spark Plug

1. Why I Pay Attention to the Spark Plug

When I look at my FS38 Stihl weed eater, I know the spark plug is one of the smallest parts that can make the biggest difference. If the engine is hard to start, runs rough, or loses power, I always check the spark plug first. A good spark plug helps my trimmer start easier, run smoother, and stay reliable during yard work.

2. What I Look for Before Buying

Before I buy a replacement, I make sure the spark plug matches my FS38 model. I check the owner’s manual or the old plug for the correct part number and size. I also pay attention to:

  • Thread size and reach
  • Heat range
  • Electrode type
  • Brand compatibility

For me, getting the exact match matters because the wrong plug can cause poor performance or starting problems.

3. OEM vs. Aftermarket Spark Plugs

I usually compare original Stihl spark plugs with aftermarket options. OEM plugs give me peace of mind because they are designed for the FS38. Aftermarket plugs can be cheaper, but I only consider them if they have strong reviews and clear compatibility. In my experience, saving a little money is not worth it if the plug causes engine trouble.

4. Signs I Need a New Spark Plug

I don’t wait until my trimmer completely fails. I replace the spark plug when I notice:

  • Hard starting
  • Misfiring or sputtering
  • Poor acceleration
  • Black carbon buildup
  • Excessive fuel use

If my weed eater is acting up and the plug looks worn, I replace it right away.

5. Build Quality Matters to Me

I prefer spark plugs made with durable materials that can handle heat and wear. A solid metal body and a clean, well-made electrode help me trust that the plug will last longer. I also avoid plugs that look cheaply made or have unclear product details.

6. Easy Installation Is a Plus

I like spark plugs that are easy to install with basic tools. If I can remove the old plug, check the gap, and install the new one without trouble, that saves me time. I always make sure the plug is properly tightened, but not over-tightened.

7. Price vs. Value

I don’t always go for the cheapest spark plug. Instead, I look for the best value. A slightly higher-priced plug is worth it to me if it starts better, lasts longer, and reduces engine issues. For a small part like this, reliability matters more than saving a few dollars.

8. My Final Buying Tip

My best advice is to buy a spark plug that is confirmed to fit the FS38 Stihl weed eater, comes from a trusted brand, and has good customer feedback. When I choose the right plug, my trimmer performs better and I spend less time fixing problems and more time getting the job done.

Final Thoughts

I’ve found that choosing the right spark plug for the FS38 Stihl weed eater makes a big difference in how smoothly the engine runs and how easy it is to start. My key takeaway is to always match the correct spark plug type, check it regularly, and replace it when it shows wear. Taking a little time for this simple maintenance can help keep the trimmer running reliably and extend its life.

Author Profile

Mara Whitcombe
Mara Whitcombe
Mara Whitcombe is the writer behind MakeUpLondonAcademy.com. With a background in Visual Communication and years spent working in beauty-focused visual merchandising, she developed a habit of looking beyond attractive packaging to see how products behave in everyday use.

Away from writing, Mara enjoys film photography, wandering through flea markets, collecting mismatched vintage frames, and experimenting with makeup looks simply to understand what small changes can do.

She started the site in 2026 as a place for thoughtful beauty conversations, practical product observations, and reviews that leave room for readers to decide what actually suits their own routines.