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Spark Plug Gap for High Performance 2-Stroke Outboards

Updated: Nov 24, 2023

A spark plug gap that is too small can cause the spark to not ignite the air-fuel mixture. However, a gap that is too large can cause the spark to be blown out at high speeds.

The recommended gap for a high-performing 2-stroke outboard is between 0.030" and 0.042". However, manufacturers' recommendations for specific engines can vary.

A good starting point is 0.035". You can experiment with different gaps to see what works best for your engine.

A smaller gap ensures that the spark plug fires on each cycle. However, if the gap is too small, there is not enough room for the air-fuel mixture.

If the gap between the electrodes of a spark plug is too small, the spark may be too weak to complete the combustion process. This can cause:

  • Partial ignition

  • Low power

  • Misfires

  • Spark plug fouling

  • Increased plug wear

  • Poor gas mileage

A larger gap creates a longer spark arc, but it requires a higher voltage to fire. This can also put a strain on the ignition parts, such as the coil, stator, and wires.

A spark plug gap that is too wide can cause the spark to lose strength as it crosses the gap. This can lead to:

  • Engine hesitation

  • A rough-running engine

  • Misfires at high speeds

  • A miss at higher rpm

  • A loss of power

  • Increased plug wear

  • Poor gas mileage

If the ignition system can't provide the voltage needed, or if turbulence in the combustion chamber blows out the spark, misfires will occur that decrease overall performance, ETs, and lap times.

An engine runs best with the widest gap that the ignition can reliably fire. Spark plugs that are gapped incorrectly can cause an engine to miss or run erratically.

Note: When gapping a plug be careful not to damage the precious metals tip, like iridium, platinum, silver, or ruthenium. Or weaken the j-gap by repeatedly bending open and closed while finding your ideal gap.

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