Understanding Positive and Negative Pulses

 


Based on the image and your question, let's break down the pulse mechanism and how it affects ignition timing for your Yamaha 125ZR with a 59mm bore.

Understanding Positive and Negative Pulses

  • The positive pulse is generated by the leading edge of the trigger bar (as shown in the left diagram).
  • The negative pulse is generated by the trailing edge of the trigger bar (as shown in the right diagram).

These pulses define:

  1. Static Angle (Base Timing): Controlled by the positive pulse, determining your initial ignition timing (e.g., 10 degrees BTDC in your stock setup).
  2. Idle and High-Speed Timing: The negative pulse defines changes to timing for idle and higher RPM operation.

Adjusting the Timing for Performance

To retard the timing for better top-end performance:

  1. Shifting the Trigger Bar:
    • Move the trigger bar clockwise relative to the rotor to delay the pulses, which retards the ignition timing.
  2. Switching Pickup Wires (if necessary):
    • If your system triggers with an initial negative pulse followed by a positive pulse, swapping the pickup wires will reverse the pulse sequence and restore proper timing polarity.
  3. Testing Setup:
    • Retard by 2 to 3 degrees from the stock 10-degree setting and test performance at high RPMs (above 8000 RPM).
    • Use a timing light to confirm the new timing position.

Pulse Mechanism for Idle and High RPMs

  • At Idle (Low RPM): The system primarily relies on the static angle defined by the positive pulse.
  • At High RPMs: The ignition controller may adjust timing by advancing or retarding based on the speed signals from the trigger bar's pulses.

Practical Tips for Your Setup

  • Initial Retardation: Set timing to around 7-8 degrees BTDC and gradually test until you find the sweet spot for high RPM performance.
  • Use a Strobe Light: Mark the rotor for 10, 8, and 6-degree positions and use the strobe to verify your adjustments.
  • Monitor Engine Behavior: Look for smoother power delivery at high RPMs and avoid knocking.

Let me know if you'd like more help with diagrams or further clarifications.

Comments

  1. Anonymous3 February 2025 at 06:31

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