FAQ
TL;DR: No‑spark on a BT49QT‑12? Expect ~300 V AC from the CDI charge coil; "AC module does not need battery power." Check up to 50 V from the pickup, inspect plug/coil, then swap the CDI if readings are good. [Elektroda, SKM 1964, #17170469]
Why it matters: This FAQ helps Baotian BT49QT‑12 and similar 50cc 4T GY6 owners quickly isolate ignition faults and get spark back.
Quick Facts
- Ignition type: AC‑CDI; spark is generated without battery power during cranking. [Elektroda, SKM 1964, #17170469]
- Typical cranking voltages: CDI charge coil ≈300 V AC; pulse generator up to ≈50 V AC. [Elektroda, SKM 1964, #17170469]
- Kill/stop (quench) wire color is black/white on this model’s loom. [Elektroda, 8850, post #17172961]
- Quick isolation test: unplug the kill/‘extinguish’ wire at the CDI connector to bypass the switch/lock. [Elektroda, SKM 1964, #17172133]
- Budget for a replacement CDI module: about 30 PLN in reported cases. [Elektroda, SKM 1964, #17173861]
How do I diagnose no-spark on a Baotian BT49QT-12 50cc 4T?
Use this quick triage:
- Measure the CDI charge‑coil output while cranking; you should see around 300 V AC.
- Check the pulse generator signal up to about 50 V AC and verify wiring continuity.
- Inspect or replace the spark plug, cap, and ignition coil, then try a known‑good AC CDI.
This sequence isolates wiring, sensors, and the module efficiently. [Elektroda, SKM 1964, #17170469]
Does the BT49QT-12 use an AC CDI, and does it need the battery to spark?
Yes. It uses an AC CDI that takes power from the stator while cranking. It does not require battery power for spark. As one expert put it, "He does not need battery power." Confirm stator outputs and ignition parts before suspecting wiring. [Elektroda, SKM 1964, #17170469]
What color wire is the kill/stop (quench) line, and what does it do?
On this loom, the black/white wire is used for engine “extinguish” (kill). It is tied into the ignition stop circuit. The owner reported disconnecting this line during testing to rule out a bad switch. [Elektroda, 8850, post #17172961]
How do I bypass the ignition switch or kill circuit to test for spark?
Unplug the single kill/“extinguish” wire from the CDI connector. Try for spark again. If spark returns, the switch or stop wiring was grounding the CDI. If nothing changes, continue with stator and module checks. [Elektroda, SKM 1964, #17172133]
Can I test a CDI module with a multimeter or repair it?
No. You cannot reliably measure a CDI at its pins with an ohmmeter. The unit is resin‑potted and not serviceable. Internal semiconductors fail and cannot be accessed. Replace the module if suspected. "You can not measure the module ... with a multimeter." [Elektroda, SKM 1964, #17170762]
What voltages should I see from the stator CDI charge coil and the pulse generator?
While kicking or cranking, expect about 300 V AC from the CDI charge coil. The pulse generator produces up to roughly 50 V. Use the multimeter AC range and back‑probe at the module connector. These readings confirm the stator and pickup signals. [Elektroda, SKM 1964, #17170469]
Should I measure voltage at the spark plug cap or “test with a finger”?
No. Avoid measuring at the plug cap and never touch it during tests. A contributor warned about people putting a toe or finger in the cap and advised against it. Use a spark tester or a grounded plug to check spark. [Elektroda, SKM 1964, #17173861]
What should I check on the ignition coil, plug cap, and spark plug?
Inspect the ignition coil for cracks and secure terminals. Check the plug cap (“finger/pipe”) for damage or looseness. Replace the spark plug with a known‑good one. These parts are inexpensive and common failure points. Swap a spare coil if available to compare. [Elektroda, SKM 1964, #17170469]
Should I check the pulse generator resistance before buying a new CDI?
Yes. Confirm the pulse generator’s continuity and that it outputs a signal. Also verify the CDI receives power from the engine. Doing these checks first prevents unnecessary parts purchases. Proceed to a CDI swap only after validation. [Elektroda, rafcio_21, post #17174343]
How much does a replacement CDI module cost for these Chinese scooters?
Expect around 30 PLN for a basic AC CDI module, according to contributor experience. Prices vary by seller and brand. This low cost makes swapping the CDI a practical diagnostic step after measurements. [Elektroda, SKM 1964, #17173861]
Where can I find the AC CDI module pinout or wiring diagram?
Search for “AC ignition module pinout” and GY6 diagrams online. As noted, “Enter the AC ignition module and you have.” Many graphics show connector layout and wire colors. Match your harness carefully before testing. [Elektroda, SKM 1964, #17170762]
What finally fixed the no-spark in this thread?
After confirming the pulse generator resistance was okay, replacing the ignition module restored spark. The engine started and ran normally. This supports CDI replacement after verifying stator and pickup signals. [Elektroda, 8850, post #17190516]
But I advise against such things. 