Ignition timing

 Here's a detailed yet simple summary of the "Ignition" section from the provided Two-Stroke Tuner's Handbook:

Ignition Fundamentals

Two-stroke engines face unique ignition challenges since they fire twice as often as four-stroke engines at the same crankshaft speed. This leads to increased wear on breaker points and a higher heat load on spark plugs. Additionally, spark plugs in two-stroke engines must deal with baked oil fog that forms semi-conductive layers on the insulator, making reliable sparking more difficult.

Ignition Systems

  1. Battery-and-Coil Ignition Systems:

    • Uses battery power to trigger the coil, which transforms the low voltage into high voltage to fire the spark plug.
    • Efficient for moderate speeds but struggles in racing conditions due to slow voltage rise and sensitivity to semi-fouled plugs.

  2. Magneto Ignition Systems:

    • Common in racing due to faster voltage rise compared to battery-and-coil systems.
    • They are less prone to voltage leakage on semi-fouled spark plugs, making them more reliable at high speeds.

  3. Capacitor Discharge (CD) Ignition:

    • Uses transistors and capacitors to release high voltage rapidly to the spark coil.
    • Effective but requires precise timing using a strobe light.

  4. Energy Transfer Magnetos:

    • Developed for high-altitude engines but adapted for motorcycles.
    • Delivers voltage in about 35-40 microseconds, much faster than battery-and-coil systems.

Spark Plugs

  • Correct spark plug selection is crucial. Racing plugs have short insulators to avoid overheating but may foul easily under certain conditions.
  • Platinum-tipped plugs are recommended for racing as they are more resistant to fouling and provide more reliable sparks.

Ignition Timing

  • Advancing Timing: Increases mid-range power but reduces top-end performance.
  • Retarding Timing: Provides smoother power delivery and better high-rpm performance.
  • Proper timing adjustment requires testing, often starting with a slight retardation from the manufacturer’s specifications and gradually advancing for optimal results.

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