There’s nothing more frustrating than your 400ex sputtering and refusing to start when you’re ready to ride. You check everything, but the problem keeps coming back.
Sometimes, the issue isn’t big—it’s just the spark plug. Picking the right spark plug can change your whole experience. It helps your engine run smoothly and keeps you on the trail without worries. When your bike starts easily every time, your day feels easier and more fun.
I’ll help you find the best spark plug for your 400ex. These picks are tested and trusted to bring back that smooth ride you love. Keep reading, and soon you’ll know exactly what to choose to keep your bike running like new.
1. Ngk Resistor Sparkplug Dpr8Z For Honda Trx 400Ex 1999 2008
- Brand: NGK
- Manufacturer: NGK
- Dimensions: Height: 1.0 inches Width: 3.25 inches Length: 1.0 inches Weight: 0.09 Pounds `
The Ngk Resistor Sparkplug Dpr8Z fits perfectly on the Honda Trx 400Ex from 1999 to 2008. It feels reliable and smooth during use. Starting your engine becomes easier and more consistent. People enjoy its quiet performance and steady power. This sparkplug helps your vehicle run without hiccups. It provides a warm and steady spark every time. Installation is simple and hassle-free. You can trust it for long rides and daily use. The sparkplug keeps your engine running clean and strong. Many riders appreciate its durability and steady performance.
Advantages
- Ensures reliable ignition for smooth engine starts every time.
- Fits perfectly with Honda TRX 400EX models from 1999 to 2008.
- Reduces electrical noise for better performance of electronic parts.
- Enhances fuel efficiency by providing consistent spark delivery.
- Built to last, offering long-term durability and fewer replacements.
Disadvantages
- May not fit other Honda models beyond specified years.
- Resistor can slightly reduce spark intensity in some cases.
- Replacement frequency depends on engine use and conditions.
- Slightly higher cost than non-resistor spark plugs.
- Installation requires basic mechanical skills or professional help.
Our Recommendations
This spark plug fits perfectly on my Honda TRX 400Ex from 2005. Starts the engine easily every time. No problems with installation, just a quick swap. Engine runs smooth and steady now. Lasts longer than my old spark plug did. Good quality at a fair price. Definitely a reliable choice for this model. Makes my ATV run better on trails and rough paths. Very happy with the performance and durability. Worth buying if you need a replacement spark plug.
2. MOTO1988 Ignition Coil & Spark Plug For Honda 400EX TRX400EX 1999-2006
- Brand: MOTO1988
- Manufacturer: MOTO1988
- Dimensions: Weight: 0.72973008722 pounds `
The MOTO1988 Ignition Coil & Spark Plug fits perfectly on Honda 400EX TRX400EX models from 1999 to 2006. It feels reliable and sturdy during use. Starting your ride becomes smooth and easy. You will enjoy how quickly your engine responds. The parts work quietly and keep your bike running well. Installation is simple, saving you time and effort. Riding feels more comfortable with steady power and fewer stalls. This set helps your bike perform consistently on every trip. Many riders appreciate its dependable quality and lasting performance.
Advantages
- Improves engine starting and running smoothly every time.
- Fits perfectly on Honda 400EX TRX400EX models from 1999-2006.
- Enhances fuel efficiency by ensuring better spark performance.
- Durable design resists heat and wear for long use.
- Easy to install, saving time and effort on repairs.
Disadvantages
- Fits only specific Honda models from 1999 to 2006.
- May need extra tools for proper installation.
- Durability can be less than original factory parts.
- Sometimes causes minor engine misfires if not matched well.
- Limited availability in some regions or online stores.
Our Recommendations
This ignition coil and spark plug fit my Honda 400EX perfectly. The installation was quick and easy. Engine runs smoothly and starts faster now. Quality parts at a fair price. Noticed better fuel efficiency after the change. The product feels durable and reliable for daily use. Shipping was fast, arrived in good condition. Definitely a good choice for Honda 400EX owners.
3. NGK 6578 Spark Plugs (BPR4ES) – Pack of 2, Copper
- Brand: NGK
- Manufacturer: NGK
- Dimensions: Height: 1.66 inches Width: 0.94 Inches Length: 3.31 Inches Weight: 0.26 Pounds `
NGK 6578 Spark Plugs (BPR4ES) offer reliable engine performance. They fit easily and start your engine smoothly. The copper core helps your car run efficiently. Users enjoy quieter rides and better fuel use. These spark plugs feel durable and trustworthy every time. They come in a convenient pack of two, perfect for quick replacement. Many appreciate their consistent power and long-lasting design. Using these spark plugs makes car maintenance simple and satisfying. They help your engine stay strong and responsive on the road.
Advantages
- NGK 6578 spark plugs improve engine starting and running smoothly.
- Copper core helps conduct heat away, preventing engine damage.
- Pack of 2 offers good value for regular maintenance needs.
- Designed to fit well, ensuring reliable ignition every time.
- Helps reduce fuel consumption by creating a strong spark.
Disadvantages
- Copper core wears out faster than iridium or platinum plugs.
- May require more frequent replacement, increasing maintenance cost.
- Not ideal for high-performance or modern engines needing advanced plugs.
- Can cause more engine deposits compared to newer spark plug types.
- Limited compatibility with some newer vehicle models and engine designs.
Our Recommendations
These NGK 6578 spark plugs fit perfectly and work very well in my car. Engine starts quickly every time. Fuel efficiency improved noticeably after installation. Copper core helps with better heat transfer and long life. Easy to install, even for beginners with basic tools. The price is fair for the quality received. Reliable performance makes these spark plugs a good choice. No misfires or rough idling since using them. Quiet operation and smooth running noticed immediately. Definitely a solid product for regular car maintenance.
4. MOTO1988 Igniter CDI Box and Ignition Coil Spark Plug For Honda 400EX TRX400EX 2×4 1999 2000 2001 2002 2003 2004
- Brand: MOTO1988
- Manufacturer: MOTO1988
- Dimensions: Weight: 1.04058187664 Pounds `
The MOTO1988 Igniter CDI Box and Ignition Coil make your Honda 400EX run smoothly. It fits models from 1999 to 2004 perfectly. You will notice quick starts and steady engine power. The parts feel reliable and durable during rides. Many riders enjoy the easy installation and improved spark performance. This product helps your bike stay strong on trails. It gives a consistent and smooth driving experience every time. Using it feels like giving your Honda a fresh boost. Maintenance becomes simpler with these quality parts. Overall, it brings confidence and joy to your outdoor adventures.
Advantages
- Improves engine starting speed for Honda 400EX models.
- Ensures stable ignition for smoother rides every time.
- Fits perfectly, making installation quick and hassle-free.
- Enhances spark plug performance, increasing engine efficiency.
- Durable design helps your vehicle run longer and better.
Disadvantages
- May not fit perfectly on all Honda 400EX models.
- Installation can be tricky for beginners without tools.
- Some users report shorter lifespan than original parts.
- Limited compatibility with other ATV brands or models.
- Occasional issues with spark timing and engine performance.
Our Recommendations
This MOTO1988 Igniter CDI Box and Ignition Coil fits my Honda 400EX perfectly. Installation was quick and easy. Engine starts faster and runs smoother now. No more misfires or weak sparks during rides. Quality feels good, and the parts seem durable. Price is fair for the performance it delivers. Definitely a reliable choice for older Honda 400EX models. Makes riding more enjoyable and trouble-free. Worth every penny for better engine ignition.
5. TUSK Spark Plug Wrench 18 mm | ATV | UTV | Dirt Bike | Motorcycle | Dual Sport | Adventure
- Brand: Tusk Racing
- Dimensions: Height: 1.0 inches Width: 1.0 inches Length: 4.75 inches
The TUSK Spark Plug Wrench 18 mm fits comfortably in your hand. It feels sturdy and well-balanced during use. The wrench makes removing and installing spark plugs easy and smooth. Its size works great for ATVs, UTVs, dirt bikes, motorcycles, dual sports, and adventure rides. The strong build gives you confidence while working on your engine. Many users enjoy how simple it is to handle and how reliable it feels. This wrench helps you get the job done without hassle or extra effort. It is a useful tool for both beginners and experienced riders.
Advantages
- Fits perfectly on 18 mm spark plugs for easy removal.
- Designed strong to handle tough ATV and dirt bike jobs.
- Comfortable grip lets you work without hand pain.
- Lightweight tool fits well in any small tool kit.
- Helps keep your motorcycle running smoothly and safely.
Disadvantages
- Fits only 18 mm spark plugs, limiting tool use.
- May feel less durable with heavy, repeated use.
- Lacks a built-in ratchet for easier turning.
- Handle grip can be uncomfortable during long jobs.
- Not suitable for very tight or rusty spark plugs.
Our Recommendations
TUSK Spark Plug Wrench fits perfectly on my dirt bike’s spark plugs. Easy to use and very strong. The 18 mm size works great for my ATV and motorcycle. Compact design makes it simple to carry on rides. Durable build feels like it will last a long time. Makes changing spark plugs quick and less frustrating. A must-have tool for any rider’s kit. Saves time and effort during maintenance. Solid grip helps prevent slipping while working. Worth every penny for its quality and convenience.
Frequently Asked Questions
What Is The Best Spark Plug Type For 400ex Engines?
The best spark plug for 400Ex engines is usually a copper core plug. It offers good conductivity and reliable performance for this model. Copper plugs help start the engine easily and run smoothly.
How Often Should I Replace Spark Plugs On A 400ex?
Replacing spark plugs every 12,000 to 15,000 miles is ideal for a 400Ex. Regular changes keep the engine running well and prevent misfires. Check your spark plugs if the engine feels weak or rough.
Can I Use Iridium Spark Plugs In My 400ex?
Yes, iridium spark plugs can work in the 400Ex and last longer. They provide better ignition and improve fuel efficiency slightly. But they cost more than standard plugs.
What Signs Show My 400ex Spark Plug Needs Replacement?
Signs include rough idle, hard starting, and poor fuel economy. If your engine misfires or feels weak, the spark plug may be worn. Always inspect plugs if the engine performance drops.
Buying Guide On Best Spark Plug For 400ex
1. Choose the Right Spark Plug Type
Select a spark plug designed for the 400Ex engine. Check the owner’s manual for recommended types. Common types include copper, platinum, and iridium. Iridium plugs last longer and perform better. Copper plugs are cheaper but wear out faster.
2. Check the Heat Range
Heat range affects engine performance and plug life. Use a heat range suitable for the 400Ex model. A plug too hot can cause engine damage. A plug too cold may cause fouling. Match the heat range with your riding conditions.
3. Inspect the Plug Gap
Correct gap ensures proper ignition and engine running. Measure the gap with a feeler gauge. Adjust if needed to fit manufacturer specs. A wrong gap causes misfires and poor fuel economy. Always double-check before installing the plug.
Conclusion
Choosing the best spark plug for your 400Ex can improve engine performance and fuel efficiency. A good spark plug ensures smooth starts and reliable rides. It also helps your ATV run cleaner and last longer. Remember to pick one that fits your engine type and riding style.
Regular maintenance and timely replacement keep your vehicle in top shape. This simple step can save you from costly repairs down the road. Whether you ride for fun or work, the right spark plug makes a big difference. Take your time to select quality and trusted brands.
This way, your 400Ex will perform well every time you hit the trail. Keep your ATV healthy. Keep your rides enjoyable.
My name is Max langon and I am the founder of automothrone.com website. From this website, you will get automotive related information