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How to Check CDI on a Yamaha Warrior

by Chris Gilliland

Yamaha's Warrior ATV series operates on a CDI system to ignite its spark plug during operation. A weak or absent spark is a symptom of problems occurring within the CDI unit or the ignition system. Unfortunately, there is no easy way to determine if the CDI unit itself is at fault or if the loss of spark was created elsewhere along the ignition system. Troubleshooting your Warrior's ignition system takes a fair amount of patience and familiarity with your machine's electronic system.

Step 1

Remove the seat using the seat release latch on the left side of the seat. Remove the fuel tank and its cover using a socket wrench to remove the bolts on the base and neck of the tank. Remove the headlight assembly and front fender from the ATV using a socket wrench to remove all bolts.

Step 2

Inspect the ATV's ignition system for damage, looking specifically for chafed, broken or damaged wires. Repair any damaged wires with electrical tape. Check the ignition system's connectors, plugging any loose connectors securely into place as needed.

Step 3

Test the battery with a multimeter set to 20 volts DC. Attach the meter's red lead to the battery's positive terminal and the black lead to the negative terminal. Charge or replace the battery if the voltage is lower than 12.5 volts DC.

Step 4

Unplug the spark plug cap from the spark plug and remove the spark plug from the motor with a spark plug socket. Inspect the spark plug for signs of obvious damage or excessive fouling, a thick black coating over the electrodes. Replace the spark plug if it is damaged or fouled. Using a spark plug gap tool, measure the distance between the spark plug's electrodes. Adjust the gap .06 mm with the gap tool if needed. Screw the spark plug back into the motor with a spark plug socket.

Step 5

Plug a spark plug tester into the spark plug cap and connect the opposite end to the side of the motor's cylinder. Set the tool's gap to 6 mm and start the motor. Observe the tool for spark. If a spark is present, the ignition system is operating properly. Remove the spark plug tester from the spark plug cap. Pull the cap off of the ignition coil wire and test the cap's resistance with a multimeter set at Ω x 1k. Replace the spark plug cap if the resistance is different than 10k Ω.

Step 6

Follow the ignition coil wire to the ignition coil. Disconnect the coil's range wire from the ATV's wiring harness. Set the multimeter to Ω x 1 and place the red lead on the coil's orange wire. Place the black lead on the ignition coil's body. Replace the ignition coil if resistance is beyond 0.36 to 0.48 Ω. Set the multimeter to Ω x 1k and move the red lead to the end of the ignition coil wire. Replace the ignition coil if resistance is beyond 5.44 to 7.36 Ω.

Step 7

Disconnect the magneto from the ATV's wiring harness and test it with a multimeter set to Ω x 100. Place the meter's red lead on the magneto socket's white and green wire. Place the black lead on the red wire. Replace the magneto's source coil if the resistance is beyond 220 to 330 Ω. Move the red lead to the blue wire and the black lead to the yellow wire. Replace the magneto's pickup coil if the resistance is beyond 170 to 209 Ω.

Replace the CDI unit if all off the components checked in the previous steps are within specifications.

Items you will need

  • Socket wrench and sockets
  • Electrical tape
  • Multimeter
  • Spark plug socket
  • Spark plug
  • Spark plug gap tool
  • Spark plug tester
  • Spark plug cap
  • Ignition coil
  • Magneto source coil
  • Magneto pickup coil
  • CDI unit

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