Which NGK spark plug heat range?

April 14, 2026 Laurens JMPB

If you ride a classic moped, you know that the right spark plug is essential for a properly running engine.
NGK has been the standard for reliable Spark plugs for many years, and the right choice can make the difference between smooth riding and poor starting.

Standard spark plug choice

For many classic mopeds (such as Tomos, Puch, Zündapp), these NGK spark plugs are commonly used:

• NGK B6HS
• NGK B7HS
• NGK B8HS

The main difference is the heat range of the spark plug.

What does the heat range mean?

Lower number (e.g. B6HS)
→ Hotter spark plug
→ Retains more heat

Higher number (e.g. B8HS)
→ Colder spark plug
→ Dissipates heat faster

Guideline based on engine capacity (cc)

50CC (standard)
→ NGK B6HS / B7HS
✔ Best choice for original engines
✔ Good starting and stable running

60CC – 65CC (lightly tuned)
→ NGK B7HS
✔ Nice middle ground
✔ Helps prevent the spark plug from getting too hot

70CC – 75CC (sport/tuned)
→ NGK B7HS / B8HS
✔ B8HS for longer rides or higher load
✔ B7HS for normal use

80CC+ (heavily tuned / race)
→ NGK B8HS (or colder)
✔ Needed to dissipate heat properly
✖ Less suitable for short rides

What happens if you use the wrong spark plug?

Too hot a spark plug:

• Risk of pinging or detonation
• Risk of seizure
• Engine runs too hot

Too cold a spark plug:

• Poor starting
• Spark plug fouls black
• Hesitation or power loss

Spark plug tuning & inspection

• Light brown / coffee brown → Perfect tune
• Black → Too rich or spark plug too cold
• White / grey → Too lean or spark plug too hot (dangerous!)

Commonly used combinations

With the right NGK spark plug matched to your engine capacity, you get the most out of your engine and prevent damage.