Harley Davidson FLS Softail Slim (2012-2017) Spark Plug Replacement Guide
Get your Twin Cam engine firing perfectly with the right set of new aftermarket spark plugs.
- Replacing spark plugs is a simple, quick, and inexpensive maintenance item you can do yourself.
- High-quality aftermarket plugs from NGK (DCPR7E, DCPR7EIX) and Champion (RA8HC) are reliable alternatives to more expensive OEM plugs.
- Always check and set the spark plug gap to ~0.040" before installation, even if the plugs are new.
- Use a torque wrench to tighten plugs to 12-18 ft-lbs to avoid damaging the engine's cylinder heads.
Is Your Softail Slim Trying to Tell You Something?
A spark plug is a wear item, and when it starts to fail, your bike's performance will suffer. The electrodes wear down over thousands of miles, making it harder for the spark to jump the gap. Fouling from carbon or oil can also prevent a good spark. Listen to your bike; it will let you know when it's time for a change.
Symptoms of Failing Spark Plugs:
- Engine Misfires: You might feel a hesitation or stumble, especially when you open the throttle.
- Rough Idle: The bike may shake more than usual or sound uneven when stopped.
- Hard Starting: A weak spark makes it difficult for the engine to fire up, especially when cold.
- Reduced Fuel Economy: Inefficient combustion from a poor spark means you're burning more fuel than necessary.
- Loss of Power: Your bike may feel sluggish and less responsive.
Check Engine Light and Trouble Codes
A persistent misfire can trigger your check engine light. You can check for codes yourself without a special tool. Common codes for a cylinder misfire are P0301 (front cylinder) and P0302 (rear cylinder). While a bad spark plug is a common cause, these codes can also point to other ignition or fuel system issues.
Choosing the Right Aftermarket Spark Plugs
For the 2012-2017 FLS Softail Slim, you have a few solid aftermarket choices that meet or exceed the quality of the original equipment (OEM) plugs. Harley's OEM 6R12 plug is made by Champion, so any direct aftermarket replacement from a reputable brand is a safe bet.
Brand Tiers
- Tier 1: Premium Aftermarket (NGK Iridium): NGK's Iridium IX plugs (part #DCPR7EIX) are a popular upgrade. The iridium tip is extremely durable, providing a longer service life and a very stable spark. While you may not feel a huge power gain, many riders choose them for their longevity and reliability. They are the most expensive option but are often worth it for peace of mind.
- Tier 2: Standard Aftermarket (NGK & Champion): This is the sweet spot for most riders. The NGK DCPR7E and the Champion RA8HC are standard copper plugs that work great in the Twin Cam engine. They offer performance identical to the OEM plug at a lower price. Many experienced mechanics and riders trust NGK's standard plugs for their consistent quality.
OEM vs. Aftermarket Quality
Harley-Davidson does not manufacture its own spark plugs; they are rebranded from a major manufacturer, widely known to be Champion. High-quality aftermarket brands like NGK and Champion offer plugs that are equivalent, and in the case of iridium plugs, superior in material and lifespan to the stock parts. There is no loss in quality by choosing a reputable aftermarket plug for your Softail Slim.
Cost of Replacement Spark Plugs
| Part Type | Price Range (Per Plug) | Notes |
|---|---|---|
| New OEM (Harley 6R12) | $6 - $10 | A reliable stock replacement, typically made by Champion. |
| New Aftermarket (Standard Copper) | $3.91 - $8.00 | Excellent value. Includes plugs like the NGK DCPR7E and Champion RA8HC. |
| New Aftermarket (Iridium) | $9.00 - $14.32 | Longest lasting option. Includes plugs like the NGK DCPR7EIX. |
Frequently Asked Questions (FAQ)
How often should I replace the spark plugs on my Softail Slim?
Harley's official recommendation varies, but it's often cited as every 30,000 miles or every two years. However, many owners find the plugs last much longer. A good practice is to inspect them every 10,000 miles and replace them when they show signs of wear, such as a rounded electrode or heavy deposits.
Do I need to gap new spark plugs?
Yes, always check the gap before installation. Most plugs come pre-gapped, but they can be knocked out of spec during shipping. The correct gap for the Twin Cam 103 engine is 🎬 Watch: How to change and gap plugs on a 103 Twin Cam 0.038" to 0.043". Aim for 0.040". Use a feeler gauge to check and a gapping tool to adjust if needed.
Is replacing the spark plugs a DIY job?
Absolutely. This is one of the easiest maintenance tasks you can perform on your Harley. The plugs are easily accessible on the side of the engine. 🎬 Watch: A helpful walkthrough of the spark plug change process The entire job can be done in under 30 minutes with basic tools.
🎬 See this step-by-step spark plug replacement on a Softail SlimWhat tools do I need to change the spark plugs?
You will need a 5/8" spark plug socket, a ratchet with an extension, a torque wrench, and a spark plug gapping tool/feeler gauge. Applying a small amount of anti-seize compound to the new plug's threads is also highly recommended to prevent them from getting stuck in the aluminum heads.
Were there any recalls for spark plugs on the 2012-2017 FLS Softail Slim?
No, there have been no specific recalls or technical service bulletins (TSBs) issued by Harley-Davidson or the NHTSA for spark plug issues on the 2012-2017 FLS Softail Slim.
Helpful Videos
Technical Specifications
OEM Part Numbers: 32362-04A 6R12
<ul><li>Aftermarket Part Numbers: NGK DCPR7E, NGK DCPR7EIX, Champion RA8HC</li><li>Thread Size: 12mm</li><li>Socket Size: 5/8" (16mm)</li><li>Recommended Gap: 0.040" (0.038"-0.043")</li><li>Installation Torque: 12-18 ft-lbs</li></ul>
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Harley Davidson FLS Softail Slim:
- 🎬 Helpful Videos
- 🛍️ Shop This Part
- Is Your Softail Slim Trying to Tell You Something?
- Symptoms of Failing Spark Plugs:
- Check Engine Light and Trouble Codes
- Choosing the Right Aftermarket Spark Plugs
- Brand Tiers
- OEM vs. Aftermarket Quality
- Cost of Replacement Spark Plugs
- Frequently Asked Questions (FAQ)
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