Yamaha YZF R125 No spark

   

Yamaha YZF R125 Workshop Manuals on Ebay UK

R125 will not start not sparking 

R125 Ignition system wiring diagram ( Spark )

⚠️ Safety Warning: When testing for spark, do not hold the spark plug wire or cap with your bare hands while cranking the engine, as this can deliver a painful electric shock. Always ground the plug against a clean part of the engine frame.

Troubleshooting "No Spark" on the Yamaha YZF-R125

If your R125 cranks over but refuses to fire, a "no spark" condition is often to blame. Before buying expensive electronics, follow this logical path to find the break in the ignition circuit.

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1. The "Quick Wins" (Basics)

Don't overlook the simple things. Many "dead" bikes are fixed in minutes by checking these:

• Kill Switch: Ensure it’s in the "RUN" position. Toggle it back and forth to clean the internal contacts.

• Fuses: Pull every fuse out. Don't just look at them; clean the metal legs and spray the fuse box with contact cleaner.

• Battery Voltage: A weak battery might turn the engine over but not have enough power left to trigger the ECU. A healthy battery should read 12.6V–12.8V resting.

• Wiring Connectors: Unplug the main loom connectors, spray them with contact cleaner, and reconnect. This solves a surprising number of intermittent faults.

2. The Safety Interlocks

The ECU will purposefully kill the spark if it thinks the bike is unsafe to start.

• Side Stand Switch: If this is faulty or clogged with road grime, the bike won't spark. Test for continuity with a multimeter.

• Neutral Switch: Ensure the neutral light is on. If the bike doesn't "know" it's in neutral, it may block the ignition.

3. The Pick-Up Coil (Crank Sensor)

This is the most common "invisible" failure. This sensor tells the ECU when to fire the spark.

• Test: Measure the resistance between the White and Pink wires at the stator connector.

• Spec: You should see 248Ω–372Ω. If it’s "OL" or open, the sensor is dead.

4. Ignition (HT) Coil & Spark Plug Cap

• Spark Plug: Always try a brand-new NGK plug first.

• HT Coil: Check the primary side for 12V while cranking. If you have 12V but no spark, the coil or the HT lead is likely faulty. If you don't have 12V, the problem is further back (ECU or wiring).

• Cap: The spark plug cap can unscrew from the lead. Ensure it’s tight and the internal resistor hasn't failed.

5. The ECU (CDI)

The ECU is rarely the first thing to fail. Only consider replacing the ECU if you have confirmed that the battery, fuses, switches, pick-up coil, and HT coil are all functioning perfectly. If possible, test with a "known good" unit from a friend's bike before purchasing.

6. Ignition Switch

Check the back of the ignition barrel. Corroded wires here can prevent the "ON" signal from reaching the ECU, even if the dash lights up.

100% Charged 12.60 to 12.8v

75% Charged 12.4v

50% Charged 12.1v

25% Charged 11.9v

0% Charged less than 11.8v

Here is an Excellent video on NO spark fault finding watch it all !!

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 electrics buy it read it and learn !!