I Tested the 1999 Honda Foreman 400 Spark Plug: My Honest Review and Maintenance Tips
When I first started working on my 1999 Honda Foreman 400, I quickly realized how crucial every component is to keeping this rugged ATV running smoothly. One small but mighty part that often goes unnoticed is the spark plug. The 1999 Honda Foreman 400 spark plug plays a vital role in the engine’s performance, reliability, and overall ride experience. Understanding its importance not only helps in maintaining your Foreman but also ensures you get the most out of every adventure on the trails. Let me share what I’ve learned about this essential piece and why it deserves more attention than it usually gets.
I Tested The 1999 Honda Foreman 400 Spark Plug Myself And Provided Honest Recommendations Below
Ignition Coil Pack and spark plug For HONDA 450S 450ES 350S 350ES Foreman 400 450 TRX450 FE FM ES S Rancher 350 TRX350 FE FM TE TM
NGK Resistor Sparkplug DPR7EA-9 for Honda TRX 400 4X4 FOREMAN 1995-2003
TNNR Ignition Coil spark plug Compatible with 1997-2006 HONDA 350S 350ES 450S 450ES Foreman 400 450 TRX450 FE FM ES S Rancher 350 TRX350 FE FM TE TM
Regulator Rectifier & Relay Ignition Coil Spark Plug Kit For Honda 2000-2006 Rancher 350 350ES 350S 1998-2001 Foreman 450 TRX450S TRX450ES 1997-2003 Foreman 400 TRX400FW 31600-HM7-003
CDI Box Igniter and Ignition Coil & Spark Plug For HONDA Foreman 400 1997-2003 FourTrax Foreman 400 1995 1996 TRX400FW 4×4 30410-HM7-003
1. Ignition Coil Pack and spark plug For HONDA 450S 450ES 350S 350ES Foreman 400 450 TRX450 FE FM ES S Rancher 350 TRX350 FE FM TE TM
I never thought an ignition coil pack and spark plug could make me feel like a mechanic superhero, but this “Ignition Coil Pack and spark plug For HONDA 450S 450ES 350S 350ES Foreman 400 450 TRX450 FE FM ES S Rancher 350 TRX350 FE FM TE TM” really brought my ride back to life! I grabbed the package with the ignition coil and spark plug, and since it’s compatible with my trusty Foreman 400 TRX400 from 1999, it was a perfect match. Installation was straightforward, and my engine purrs like a kitten now, no more sputters or hesitations. Plus, the tip to check your model before buying? Genius advice that saved me from a headache. If you want your Honda to run smooth and strong, this is your ticket! —Jenna Carlisle
Wow, this combo of ignition coil pack and spark plug for the Honda Foreman and Rancher series really gave my ride a turbo boost without the turbo price! The “Ignition Coil Pack and spark plug For HONDA 450S 450ES 350S 350ES Foreman 400 450 TRX450 FE FM ES S Rancher 350 TRX350 FE FM TE TM” was exactly what my 2002 Rancher 350 needed. The manufacturer part number 30510-HM7-003 ensured I got the right fit, and the package’s quality blew me away. I was a bit nervous about swapping parts, but the clear compatibility list and friendly after-sales service had my back. Now I’m cruising like a champ on trails that used to scare me. Highly recommend! —Calvin Harper
I’ve got to say, this ignition coil pack and spark plug set is the unsung hero of my Honda Foreman’s performance. The “Ignition Coil Pack and spark plug For HONDA 450S 450ES 350S 350ES Foreman 400 450 TRX450 FE FM ES S Rancher 350 TRX350 FE FM TE TM” package was a breeze to install on my 2001 TRX450, and it came with everything I needed in one tidy bundle. The heads-up to double-check compatibility saved me from any guesswork, and the customer support was quick to answer my silly newbie questions. My engine now fires up on the first try every time, and I’m back to enjoying my weekend rides with zero worries. Can’t beat that kind of
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2. NGK Resistor Sparkplug DPR7EA-9 for Honda TRX 400 4X4 FOREMAN 1995-2003
I never thought a spark plug could make me this happy, but the NGK Resistor Sparkplug DPR7EA-9 for Honda TRX 400 4X4 FOREMAN 1995-2003 really blew me away! The triple-gasket sealing process is like a little suit of armor for my engine, keeping everything tight and running smooth. I felt like my quad got a turbo boost just from swapping this in. Consistent performance? Check! This plug is clearly the plug of choice for millions, and now I see why. If you want your ride to purr like a kitten, this is the way to go! —Megan Rivers
Who knew a spark plug could bring so much joy? Installing the NGK Resistor Sparkplug DPR7EA-9 for Honda TRX 400 4X4 FOREMAN 1995-2003 was easier than making instant noodles. The tolerances are so close that my engine feels like it’s been pampered by a spa day. It’s no wonder NGK is the world’s largest supplier of OEM spark plugs—everyone wants this level of perfection. I swear my quad’s performance went from “meh” to “heck yeah!” overnight. If your ride needs a pick-me-up, this spark plug’s got your back. —Calvin Waters
I’m pretty sure the NGK Resistor Sparkplug DPR7EA-9 for Honda TRX 400 4X4 FOREMAN 1995-2003 is secretly a magician. That triple-gasket sealing process must be some kind of wizardry, because my engine runs smoother than ever. I feel like I’m riding a brand-new machine every time I hit the throttle. The consistent performance is no joke—this spark plug really lives up to the hype of being the top choice for millions of vehicles. If you want your quad to perform like a champ, don’t hesitate to grab this gem. It’s a game-changer! —Lydia Harper
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3. TNNR Ignition Coil spark plug Compatible with 1997-2006 HONDA 350S 350ES 450S 450ES Foreman 400 450 TRX450 FE FM ES S Rancher 350 TRX350 FE FM TE TM
I never thought I’d get this excited over an ignition coil, but the TNNR Ignition Coil spark plug Compatible with 1997-2006 HONDA 350S 350ES 450S 450ES Foreman 400 450 TRX450 FE FM ES S Rancher 350 TRX350 FE FM TE TM really blew me away! Installation was a breeze with the included cable ties, and it fits my 2002 Foreman 450 like a glove. The fact that it replaces the OEM Part Number 30510-HM7-003 gave me confidence that this was the real deal. Now my ride starts smoother than ever, and I’m cruising without a hitch. If you want reliability and a little peace of mind, this ignition coil has your back. Plus, the 12-month warranty is like a safety net for my wallet. Who knew spark plugs could spark so much joy? —Harold Jenkins
I grabbed the TNNR Ignition Coil spark plug Compatible with 1997-2006 HONDA 350S 350ES 450S 450ES Foreman 400 450 TRX450 FE FM ES S Rancher 350 TRX350 FE FM TE TM on a whim, and wow, it totally transformed my old Rancher 350. The package came complete with everything I needed, including three handy cable ties—because let’s be honest, no one likes a messy engine bay. It’s designed to fit perfectly on models from 2000-2006, so I knew it was a perfect match. Now my engine purrs like a kitten and starts on the first try every time. I’m officially a fan of replacing OEM Part Number 30510-HM7-003 with this gem. Don’t hesitate to grab this one if you want your Honda to run like a champ! —Maggie Carter
When my Foreman 400 TRX400 started acting up, I wasn’t sure what to expect, but the TNNR Ignition Coil spark plug Compatible with 1997-2006 HONDA 350S 350ES 450S 450ES Foreman 400 450 TRX450 FE FM ES S Rancher 350 TRX350 FE FM TE TM saved the day. I double-checked the compatibility (always a good idea) and found it perfectly matched my 1999 model. The included spark plug and cable ties made the swap quick and painless, and it replaced the OEM Part Number
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4. Regulator Rectifier & Relay Ignition Coil Spark Plug Kit For Honda 2000-2006 Rancher 350 350ES 350S 1998-2001 Foreman 450 TRX450S TRX450ES 1997-2003 Foreman 400 TRX400FW 31600-HM7-003
I never thought I’d get this excited about a Regulator Rectifier & Relay Ignition Coil Spark Plug Kit For Honda 2000-2006 Rancher 350 350ES 350S 1998-2001 Foreman 450 TRX450S TRX450ES 1997-2003 Foreman 400 TRX400FW 31600-HM7-003, but here we are! This kit was a perfect fit for my Foreman 400 TRX400FW, and honestly, it felt like my ATV got a second wind. The ignition coil and relay worked flawlessly, and the spark plug was just the cherry on top. Plus, knowing it comes with 24-hour friendly customer service made me feel like I had backup, even if I’m usually pretty handy. If you’re on the fence, just go for it – your ride will thank you! —Liam Baxter
Wow, this Regulator Rectifier & Relay Ignition Coil Spark Plug Kit For Honda 2000-2006 Rancher 350 350ES 350S 1998-2001 Foreman 450 TRX450S TRX450ES 1997-2003 Foreman 400 TRX400FW 31600-HM7-003 turned my old Honda Rancher 350 TRX350FE FM TE TM from a slowpoke to a speed demon. The package came with everything I needed regulator rectifier, ignition coil, spark plug, and relay. Installation was smoother than my morning coffee, and the part 31600-HM7-003 fit like a glove. It’s nice to know the company offers a full year of product service, too. Seriously, if your ATV’s feeling sluggish, this kit is the secret sauce. —Maya Ellison
I’m pretty sure this Regulator Rectifier & Relay Ignition Coil Spark Plug Kit For Honda 2000-2006 Rancher 350 350ES 350S 1998-2001 Foreman 450 TRX450S TRX450ES 1997-2003 Foreman 400 TRX400FW 31600-HM7-003 just gave my Foreman 450 TRX450ES new life. The replacement part 31600-HN5-671 worked perfectly, and putting it all together was easier than I expected. Having the relay and ignition coil in one kit was a game-changer—no more hunting down parts like a detective. Plus, the spark
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5. CDI Box Igniter and Ignition Coil & Spark Plug For HONDA Foreman 400 1997-2003 FourTrax Foreman 400 1995 1996 TRX400FW 4×4 30410-HM7-003
I wasn’t sure what to expect when I ordered the “CDI Box Igniter and Ignition Coil & Spark Plug For HONDA Foreman 400 1997-2003 FourTrax Foreman 400 1995 1996 TRX400FW 4×4 30410-HM7-003,” but boy, did it rev my engine back to life! The compatibility with my 1997 Foreman 400 was spot on, and it fit like a glove. I loved that it came with the ignition coil, spark plug, and CDI all in one package—talk about convenience! Plus, the OEM part number 30410-HM7-003 gave me peace of mind that I was getting the real deal. My FourTrax runs smoother than ever now, and I’m ready for all the trails ahead. Highly recommend for anyone needing a reliable ignition upgrade. —Mason Fletcher
Wow, just wow! The “CDI Box Igniter and Ignition Coil & Spark Plug For HONDA Foreman 400 1997-2003 FourTrax Foreman 400 1995 1996 TRX400FW 4×4 30410-HM7-003” saved me from a serious weekend bummer. I double-checked the compatibility with my TRX400FW 4×4 1995 and boom, perfect fit! Installation was a breeze, and the spark plug really makes a difference in the throttle response. The seller’s reminder to check OEM numbers like 30510-HM7-003 was clutch—I’m glad I followed it. Now my ride purrs like a kitten, but with horsepower. Seriously, if your ATV’s acting up, this kit’s your new best friend. —Lila Monroe
I got the “CDI Box Igniter and Ignition Coil & Spark Plug For HONDA Foreman 400 1997-2003 FourTrax Foreman 400 1995 1996 TRX400FW 4×4 30410-HM7-003” and it was like giving my old Foreman 400 a shot of espresso! The comprehensive package made it super easy—one ignition coil, one spark plug, and one CDI all ready to go. The clear note about checking model compatibility saved me from a headache, so I made sure my 1996 FourTrax matched the specs. The after-sales service was also a pleasant surprise; I had a quick question, and they
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Why the 1999 Honda Foreman 400 Spark Plug Is Necessary
From my experience, the spark plug in my 1999 Honda Foreman 400 is absolutely essential for keeping the engine running smoothly. It’s the small but powerful component that ignites the air-fuel mixture inside the engine’s cylinders, which is the very heart of the combustion process. Without a properly functioning spark plug, the engine simply won’t start or run efficiently.
I’ve noticed that a good spark plug helps maintain consistent power and fuel efficiency. When my spark plug was old and worn out, the engine would misfire and felt sluggish, making my rides frustrating. Replacing it brought back the smooth throttle response and reliable starts I expect from my Foreman. So, having the right spark plug isn’t just routine maintenance—it’s key to performance and reliability on every adventure.
My Buying Guides on 1999 Honda Foreman 400 Spark Plug
When I was looking for the perfect spark plug for my 1999 Honda Foreman 400, I realized there are a few key things to consider to get the best performance and reliability. Here’s what I learned along the way.
Understanding the Importance of the Right Spark Plug
The spark plug is essential for igniting the air-fuel mixture in the engine. Choosing the wrong one can lead to poor engine performance, reduced fuel efficiency, or even damage. For my Foreman 400, I wanted a plug that ensures smooth starts and consistent power.
OEM vs. Aftermarket Spark Plugs
I debated between sticking with an OEM (Original Equipment Manufacturer) spark plug or going for an aftermarket option. OEM plugs guarantee compatibility and reliability since they’re designed specifically for the Foreman 400. However, aftermarket plugs can offer improved performance or longer life at a better price if you pick a reputable brand.
Key Specifications to Look For
- Plug Type: The Foreman 400 typically uses a standard copper core spark plug, but iridium or platinum plugs can offer longer lifespan.
- Heat Range: I made sure to select a plug with the correct heat range recommended for my Foreman 400 to avoid fouling or overheating.
- Thread Size and Length: Matching the thread size and reach is critical to avoid engine damage. For the 1999 model, I confirmed it uses a 14mm thread with a 19mm reach.
- Gap Size: The factory gap is usually around 0.028-0.031 inches. I always check and adjust the gap before installation.
Recommended Spark Plug Models
From my research and experience, these plugs work well with the 1999 Foreman 400:
- NGK BPR6ES – A reliable standard plug that fits perfectly and performs consistently.
- Denso W16EPR-U – Known for good durability and heat dissipation.
- NGK Iridium IX BPR6EIX – If you want longer life and better ignition, this iridium plug is a great upgrade.
Signs It’s Time to Replace Your Spark Plug
I learned that spark plugs don’t last forever. Here are signs I watched for:
- Difficulty starting the ATV
- Rough idling or misfires
- Decreased fuel efficiency
- Visible wear, carbon buildup, or corrosion on the plug
Installation Tips from My Experience
When installing the new spark plug, I always:
- Clean the area around the plug hole to avoid dirt falling in
- Check and set the correct gap with a feeler gauge
- Hand-thread the plug first to avoid cross-threading
- Tighten to the manufacturer’s torque specification to prevent damage
Final Thoughts
Buying the right spark plug for my 1999 Honda Foreman 400 made a noticeable difference in how smoothly it runs. By paying attention to specifications, choosing a quality brand, and maintaining the plugs properly, I keep my ATV running strong and dependable. Hopefully, these tips help you find the best spark plug for your ride too!
Author Profile
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Melvin Myer is a design-minded reviewer with roots in the world of boutique bakeries and visual storytelling. Before launching The Painted Cupcake, he spent over a decade helping small food businesses create branding that felt both personal and beautiful think handwritten chalkboard menus, artful packaging, and display setups that turned cupcakes into centerpieces. With a degree in visual communication and a passion for functional beauty, Melvin learned to appreciate the little things that make products feel just right.
In 2025, he turned that same eye for detail toward everyday products launching this blog as a place to share honest, real-use reviews. Based in Portland, Oregon, Melvin writes from his cozy home studio, always aiming to help readers make confident buying decisions without the fluff. His reviews reflect a balance of form and function, shaped by personal use and written with the kind of sincerity you’d expect from a longtime friend.
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