NGK LFR6A Spark Plug - 6668

NGK LFR6A Spark Plug – 6668

The NGK LFR6A Spark Plug, stock number 6668, is a proven ignition replacement for select Yamaha four-stroke marine engines, including the popular 1.8L High Output powerplant used in Yamaha jet boats and WaveRunners. Designed for dependable spark delivery and efficient combustion, it helps maintain quick starting, smooth idle quality, responsive acceleration, and consistent performance throughout the RPM range.

Built with a copper-core center electrode and durable nickel firing surfaces, the LFR6A transfers heat efficiently while providing reliable ignition under demanding marine operating conditions. Its resistor construction helps reduce electrical interference with onboard electronics, making it well suited for modern Yamaha engine management systems.

Worn or fouled plugs can contribute to hard starting, hesitation, misfires, rough running, and loss of performance. Installing fresh NGK 6668 spark plugs during scheduled maintenance helps restore proper combustion and keeps your Yamaha marine engine performing as intended.

Spark Plug Specifications

• Manufacturer: NGK

• Part Number: LFR6A

• NGK Stock Number: 6668

• Type: Resistor spark plug

• Electrode Core: Copper

• Center Electrode Material: Nickel

• Ground Electrode Material: Nickel

• Heat Range: 6

• Thread Size: M14 x 1.25

• Thread Reach: 26.5 mm

• Hex Size: 16 mm / 5/8"

• Seat Type: Gasket

• Preset Gap: 0.9 mm / .036"

• Approximate Resistance: 5,000 ohms

• Sold Individually

Common Yamaha Engine Applications

The NGK LFR6A / 6668 is commonly used with Yamaha four-stroke marine engines, including:

• Yamaha 1.8L High Output

• Yamaha 1812cc HO

• Yamaha 1.8L Naturally Aspirated

• Yamaha 1812cc Four-Cylinder

• Select Yamaha 1.9L 1898cc High Output applications

Because Yamaha has used both naturally aspirated and supercharged versions of its 1.8L engine, horsepower or displacement alone should not be used to determine spark plug compatibility.

Yamaha Jet Boat Fitment

Depending on model year and installed engine package, the NGK LFR6A is commonly used in Yamaha boats such as:

Yamaha 19-Foot Models

• Yamaha AR190

• Yamaha SX190

• Yamaha 190 FSH

• Yamaha 190 FSH Sport

• Yamaha 190 FSH Deluxe

Yamaha 21 & 22-Foot Models

• Yamaha 212X

• Yamaha 212S

• Yamaha 212SS

• Yamaha 212 Limited

• Yamaha 212 Limited S

• Yamaha 212SD

• Yamaha 212SE

• Yamaha 212XE

• Yamaha 212XD

• Select Yamaha 222 Series models

Yamaha 24 & 25-Foot Models

• Yamaha AR240 High Output

• Yamaha SX240 High Output

• Yamaha 242 Limited

• Yamaha 242 Limited S

• Yamaha 242 Limited SE

• Yamaha 242X

• Yamaha 242XE

• Yamaha AR250

• Yamaha SX250

• Yamaha 252S

• Yamaha 252SE

• Yamaha 252XE

• Yamaha 252 FSH Sport

Yamaha WaveRunner Fitment

The NGK 6668 is also commonly used in compatible Yamaha WaveRunner models, including:

• Yamaha FX HO

• Yamaha FX Cruiser HO

• Yamaha FX Cruiser SHO – select applications

• Yamaha VXR

• Yamaha VXS

• Yamaha VX Cruiser HO

• Yamaha VX Limited HO

• Yamaha GP HO

• Select Yamaha GP1800 applications

Yamaha OEM Cross References

The NGK LFR6A / 6668 is commonly associated with Yamaha replacement numbers including:

• Yamaha LFR-6A000-00-00

• Yamaha 94702-00427-00

• Yamaha 94709-00427

• NGK LFR6A

• NGK 6668

Always compare the original plug or Yamaha engine specification before ordering.

Key Features

• Genuine NGK LFR6A spark plug

• NGK stock number 6668

• Popular replacement for Yamaha 1.8L HO marine engines

• Copper-core electrode provides efficient heat transfer

• Resistor construction helps suppress electronic interference

• Supports smooth starting and consistent acceleration

• Helps maintain efficient combustion under varying engine loads

• Suitable for Yamaha jet boats and WaveRunners

• Ideal for seasonal service and routine tune-ups

Dependable Ignition for Yamaha Marine Engines

Yamaha's high-output marine engines spend much of their operating life under significant load, making proper ignition maintenance especially important. Electrode wear and combustion deposits can eventually reduce spark quality, resulting in harder starts, hesitation, or diminished performance. Replacing the plugs at the appropriate service interval helps maintain the smooth power delivery Yamaha engines are known for.

Whether you're servicing an AR190, SX190, 190 FSH, 212X, AR240, SX240, 242 Limited, AR250, FX HO, VXR, or another compatible Yamaha marine application, the NGK LFR6A Spark Plug – 6668 provides proven NGK quality and reliable ignition performance.

Fitment Note: Yamaha has used different spark plugs in naturally aspirated, HO, SHO, SVHO, and other engine configurations, even when displacement is similar. Do not determine compatibility by boat or WaveRunner model alone. Verify NGK LFR6A / stock #6668 against your Yamaha engine model, year, or original OEM spark plug number before ordering.