FAQ
TL;DR: Expect >50 V between green and red at crank; "Check or disconnect the Kill Switch" to avoid shorts. This quick guide fixes no-spark on Loncin 125/Chinese CDI ignition by verifying stator, pulser, wiring, and CDI basics. [Elektroda, DriverMSG, post #17206402]
Why it matters: It prevents endless parts-swapping by confirming each ignition stage with simple measurements.
Quick Facts
- CDI charge input: Expect >50 V while cranking between the green and red wires. [Elektroda, DriverMSG, post #17206402]
- Pulser spec: Typical 120–140 Ω between blue and green; set ~0.3 mm air gap without rubbing. [Elektroda, Staszek49, post #17207003]
- LED test: A red LED across the pulser (blue/green) should flash at start; ProgCDI pulses are ~2–30 V. [Elektroda, dziechu, post #17208431]
- Kill switch: It must not short CDI pins during start; disconnect to verify. [Elektroda, DriverMSG, post #17206402]
- Wiring: Confirm loom matches the shared CDI diagram before deeper diagnostics. [Elektroda, DriverMSG, post #17206364]
What are the first checks when there’s no spark on a Loncin 125 or similar Chinese CDI?
Start with three quick checks. Measure between green and red wires while cranking; you should see over 50 V. Disconnect the Kill Switch to ensure it does not short the CDI during start. Check that the CDI sees trigger impulses on the blue wire. [Elektroda, DriverMSG, post #17206402]
How much resistance should the pickup/pulser have, and what gap is right?
Typical pulser resistance is about 120–140 Ω between blue and green. Set the air gap to roughly 0.3 mm so it does not rub. The pulser produces a brief trigger when the flywheel “hump” passes. “Do not expect high currents from the pulser.” [Elektroda, Staszek49, post #17207003]
Why does my multimeter show nothing on the blue pulser wire?
The pulser produces only a very short impulse, so many meters will not display it. As the expert noted, it is “only a minimal impulse.” Instead, measure the resistance between the blue and green pulser wires to confirm integrity. [Elektroda, DriverMSG, post #17206982]
How do I LED-test the pulser quickly?
Connect a red LED across the pulser’s blue and green wires. Crank the engine and watch for flashes. A red LED has a low turn-on voltage and will show the brief trigger. For ProgCDI systems, pulses fall in the ~2–30 V range. Test at dusk if flashes are faint. [Elektroda, dziechu, post #17208431]
What voltage should I see feeding the CDI while cranking?
Measure between the green and red wires during cranking. You should read over 50 V. Low or no voltage indicates a charging coil or wiring issue upstream of the CDI. Confirm connectors and grounds before assuming module failure. [Elektroda, DriverMSG, post #17206402]
Should I disconnect the Kill Switch during diagnosis?
Yes. The Kill Switch must not short CDI pins at start, or the ignition will be disabled. Unplug it and retest for spark and trigger signals. Reconnect only after you confirm normal readings with it isolated. [Elektroda, DriverMSG, post #17206402]
What air gap should I set between the pickup and flywheel?
Set the pickup-to-flywheel gap to about 0.3 mm. Ensure it does not touch. The trigger occurs when the flywheel’s “hump” passes the pickup, so correct spacing and alignment are critical. Recheck the mount after any flywheel work. [Elektroda, Staszek49, post #17207003]
Is ~160 Ω across the pulser out of spec?
Yes. Typical pulser resistivity is about 120–140 Ω between blue and green. A reading around 160 Ω indicates drift or a mismatched pickup. Re-verify the gap and consider replacing the sensor if spark remains absent. [Elektroda, Staszek49, post #17207003]
How can I confirm my CDI wiring is correct before testing parts?
Compare your harness to the reference diagram. Confirm wire colors and pin positions match the shared CDI layout. Fix any pin-out errors and poor connections first, as wiring faults mimic failed modules and coils. [Elektroda, DriverMSG, post #17206364]
I have no voltage from the pulser at all—what should I do?
Do not rely on live-voltage reading; the pulse is too brief. Instead, measure resistance between the blue and green pulser wires to verify the sensor. Replace the pickup if the reading is abnormal or unstable when moved. [Elektroda, DriverMSG, post #17206982]
Can a deformed or altered flywheel (“magneto”) stop the trigger?
Yes. The pickup fires only when the flywheel’s “hump” passes the sensor. If that feature is damaged or misaligned, the CDI will not receive a proper trigger. Verify flywheel condition and pickup alignment after any impact or service. [Elektroda, Staszek49, post #17207003]
Give me a 3-step quick test to isolate no-spark without swapping parts.
- Measure green-to-red while cranking; confirm >50 V.
- Disconnect the Kill Switch and retry for spark.
- Check for a trigger on the blue wire (or verify pulser resistance).
If any step fails, repair that stage first. [Elektroda, DriverMSG, post #17206402]
I replaced the CDI and coil and still have no spark—what next?
Validate inputs before suspecting new parts. Confirm the charging voltage (>50 V) on green-to-red while cranking. Isolate the Kill Switch to prevent shorts. Check that the blue pulser lead generates a trigger at start. Only after these pass should you re-evaluate CDI and coil. [Elektroda, DriverMSG, post #17206402]
Did this thread confirm a final root cause?
No final fix was reported. A later poster asked what solved it, citing no pulser output. Follow the voltage, kill-switch, and pulser checks above to identify your own root cause reliably. [Elektroda, RadziXK, post #18050128]
