Testing a 2-stroke CDI unit can seem daunting, but with a systematic approach and the right tools, you can diagnose the problem effectively. This guide will walk you through testing your CDI, along with its related components: the pickup coil, stator, and magneto. Remember safety first! Always disconnect the spark plug before working on any ignition system components.
Understanding the Ignition System Components
Before diving into testing, let's briefly understand the role of each component:
- Magneto: This is the heart of the system, generating the electrical energy. It's usually a permanent magnet rotating within coils.
- Stator: (Sometimes integrated with the magneto) This stationary component contains coils that receive the electrical pulses from the magneto. These pulses are crucial for generating the AC power.
- Pickup Coil: This coil senses the position of the flywheel (or rotor) and sends a signal to the CDI unit. It essentially tells the CDI when to fire the spark.
- CDI (Capacitor Discharge Ignition): This electronic control unit receives the signal from the pickup coil, stores energy, and then releases it to the spark plug at precisely the right moment for ignition.
Testing the Magneto and Stator
Testing the magneto and stator requires a multimeter. You'll need to consult your engine's service manual for the specific specifications (voltage and resistance values) for your model. These values vary significantly between engines.
1. Magneto Output Test:
- Safety First: Ensure the engine is disconnected from the power supply.
- Prepare: Use your multimeter set to AC volts.
- Procedure: With the engine's flywheel/rotor in place, slowly rotate it by hand. You should see an AC voltage reading across the stator's output wires. If you don't get a reading, the magneto may be faulty. The specific voltage reading should be in your service manual. A low voltage reading might indicate a weak magneto.
2. Stator Resistance Test:
- Prepare: Use your multimeter set to ohms (resistance).
- Procedure: Disconnect the stator wires. Test the resistance between each stator winding (again, consult your service manual for the specific resistance values). High or low resistance readings compared to the specifications indicate a faulty stator winding. Open circuits (infinite resistance) or short circuits (zero resistance) are definite signs of failure.
Testing the Pickup Coil
The pickup coil's test is similar to the stator test, focusing on resistance measurements.
1. Pickup Coil Resistance Test:
- Prepare: Use your multimeter set to ohms.
- Procedure: Disconnect the pickup coil wires. Your service manual will detail which wires are the pickup coil's. Measure the resistance across the pickup coil's terminals. Compare your reading to the specified value in your service manual. A high resistance value or an open circuit could indicate problems, a short circuit would mean a faulty pickup coil.
Testing the CDI Unit
Testing the CDI is the most challenging part, as it's an electronic component. A simple resistance test won't always reveal a faulty CDI. While some basic tests can be performed with a multimeter, complete testing often requires a specialized CDI tester or a comparison with a known good CDI unit.
1. Visual Inspection:
- Check for Physical Damage: Look for any obvious signs of damage like cracks, burns, or loose connections on the CDI unit.
2. Resistance Test (Limited Effectiveness):
- Prepare: Use your multimeter set to ohms.
- Procedure: Consult your service manual for specified resistance values. This is a limited test; many CDI faults won't show up.
3. The "Swap Test":
- The Best Method: If possible, try swapping your CDI with a known good one from a similar engine. If the problem is solved, the old CDI was faulty. This is often the most reliable method.
4. Using a CDI Tester (If Possible):
- Specialized Tool: A CDI tester can provide more accurate and comprehensive diagnostic information.
Troubleshooting Based on Test Results
Once you've completed the tests, analyze the results against the specifications in your service manual. Based on the failures, you can pinpoint the faulty component:
- No spark: Could be a faulty magneto, stator, pickup coil, or CDI.
- Weak spark: Could indicate a weak magneto, failing coil, or a problem with the CDI.
- Intermittent spark: Possibly a loose connection, damaged wiring, or a failing CDI unit.
Remember: Always refer to your engine's service manual for specific instructions, wiring diagrams, and resistance/voltage values. These values vary significantly between different models and manufacturers. If you are uncomfortable performing these tests, consult a qualified mechanic.
