Choosing the Right Spark Plugs for a 1968-1973 Honda CL350 Scrambler
Keep your vintage Scrambler running strong with the correct set of spark plugs for its air-cooled twin engine.
- The standard recommended spark plug is the NGK B8ES or an equivalent from Denso (W24ES-U).
- Always check and set the spark plug gap to 0.7mm-0.8mm (0.028-0.032 in) before installation.
- If using modern resistor plugs (like NGK BR8ES), you may need to switch to non-resistor plug caps to ensure a strong spark.
- Reading your old plugs can tell you a lot about your engine's health; a light tan color is ideal.
Signs of Failing Spark Plugs on a CL350
Worn or incorrect spark plugs can cause a variety of issues on your vintage Honda. Because the ignition system is relatively simple, spark plugs are often one of the first things to check 🎬 Watch: How to diagnose common ignition problems on your CL350 when you have a running problem.
- Hard Starting: Difficulty getting the engine to fire up, especially when cold.
- Engine Misfires: You may feel the engine stumble or hesitate during acceleration.
- Rough Idle: The engine may idle unevenly or stall.
- Fouled Plugs: Upon inspection, you may find the plug tips are black and sooty (carbon fouled) or wet with oil or fuel. This can point to other issues like a rich fuel mixture or worn engine components, but the plug itself will not fire correctly in this state.
- Poor Performance: A general lack of power, poor throttle response, and reduced fuel economy.
Choosing the Right Aftermarket Spark Plug
For a vintage motorcycle like the CL350, aftermarket spark plugs from reputable brands are the standard. The distinction between "OEM" and "aftermarket" is less important than choosing the correct plug with the right specifications. NGK, Denso, and Champion are all established brands available for this bike.
Brand Quality Tiers
| Tier | Brands | Assessment |
|---|---|---|
| Top Tier (Highly Recommended) | NGK, Denso | NGK is the most commonly recommended and used brand for vintage Hondas. The standard plug is the B8ES. Denso is also a high-quality Japanese brand that works well. These brands were often the original equipment for Japanese bikes of this era. |
| Standard Tier | Champion | Champion offers compatible plugs and can be a reliable choice, though they are less commonly discussed in owner forums than NGK or Denso for this specific model. |
Understanding Heat Range: B8ES vs. B7ES
The number in an NGK spark plug's name indicates its heat range. A higher number (B8ES) is a "colder" plug, while a lower number (B7ES) is a "hotter" plug. The standard recommendation for the CL350 is the colder B8ES. However, if you do a lot of short-trip, low-speed riding, your bike may be prone to carbon fouling. In these cases, some owners use the hotter B7ES plug to help burn off deposits. If your bike is tuned correctly and used for longer rides, stick with the B8ES.
A Note on Resistor Plugs (BR8ES)
The original non-resistor NGK B8ES plug has been largely discontinued and replaced by the BR8ES, which is a resistor plug. Your CL350 likely has resistor-type spark plug caps (5k ohm). Using a resistor plug (like the BR8ES) with a resistor cap can create too much total resistance, leading to a weaker spark. If you can't find non-resistor B8ES plugs, the best solution is to use the BR8ES plugs and switch to non-resistor plug caps to maintain proper ignition performance.
Cost of Aftermarket Spark Plugs for a Honda CL350 (1968-1973)
The cost for a set of two spark plugs is very reasonable. The price variation depends on the plug material (standard copper vs. iridium) and the brand.
| Part Type | Price Range (Set of 2) |
|---|---|
| New Aftermarket (Standard Copper) | $7 - $15 |
| New Aftermarket (Iridium) | $25 - $55 |
Pricing is approximate and based on a survey of online retailers. It does not include shipping or taxes.
Frequently Asked Questions (FAQ)
What is the correct spark plug gap for a CL350?
The correct spark plug gap is between 0.7mm and 0.8mm (0.028 - 0.032 inches). Always check the gap with a wire-type feeler gauge before installation.
🎬 See this pro tip for reading and gapping your plugsHow often should I replace the spark plugs?
For a standard copper plug on a vintage bike, it's good practice to inspect them every 1,500-2,000 miles and replace them annually or every 3,000-4,000 miles, whichever comes first. They are inexpensive and critical to engine health.
Are expensive iridium spark plugs worth it for my CL350?
While iridium plugs offer a longer service life, they are not necessary for the performance of a stock CL350. The bike's ignition system was designed for standard copper plugs. Given the low cost of copper plugs and the potential for fouling due to carburetor tuning, it's often more practical to stick with the standard, less expensive option and replace them more frequently.
What does the color of my old spark plug mean?
The color of the ceramic insulator is a great indicator of engine health. A light tan or chocolate brown color means everything is running well. A black, sooty plug indicates a rich fuel mixture or weak spark. 🎬 Watch: How to tune your carburetors for a better burn A white or blistered plug indicates a lean mixture or an engine that is running too hot. A wet, oily plug can be a sign of worn piston rings or valve seals.
Helpful Videos
Technical Specifications
OEM Part Numbers: NGK B8ES Denso W24ES-U
Spark Plug Gap: 0.7mm - 0.8mm (0.028 - 0.032 in)
We Have This Part in Stock
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.
- 🎬 Helpful Videos
- 🛍️ Shop This Part
- Signs of Failing Spark Plugs on a CL350
- Choosing the Right Aftermarket Spark Plug
- Brand Quality Tiers
- Understanding Heat Range: B8ES vs. B7ES
- A Note on Resistor Plugs (BR8ES)
- Cost of Aftermarket Spark Plugs for a Honda CL350 (1968-1973)
- Frequently Asked Questions (FAQ)
- 🎟️ Get 5% Off