Troubleshooting Your Motor: I’m Not Getting a Spark!
In order for your motor to start and run it needs a spark, which comes from both the magneto and the CDI. If one or both of these components aren’t working you won’t be able to start your engine (let alone use it) not matter how well it’s tuned.
I’m getting a weak spark, and my bike is sputtering:
1) Make sure you’re getting spark
To check if you are receiving power to the spark plug, follow these simple steps.
- Remove the spark plug from the cylinder head.
- Re-attach the spark plug to the spark plug cap.
- Lay the spark plug on the cylinder head so that the metal of the plug is touching any metal portion of the cylinder head. DO NOT HOLD THE SPARK PLUG OR BOOT BY HAND.
- With the clutch out, push the bike forward or turn the rear wheel. A bright spark should be visible.
2) Wiring Issue
If you’re getting a weak spark and the bike doesn’t seem to be firing the way it should, there’s a chance that the cables for the CDI, magneto, and kill switch aren’t connected correctly. Check to make sure that all of the electrical connections leading from the magneto are connected:
Blue leads to blue, black leads to black as the wires enter the CDI box from the magneto. Follow the white wire as it leads from the magneto up to the kill switch. On certain models, the kill switch may be at fault grounding out against the handlebar. Disconnect the kill switch at the handlebar and attempt to restart the bike.
If these components are connected but still don’t get a spark, try taking the stock cable connections off of each wire, peeling the housing back, and wiring the cables wire-to-wire (those cheap metal connections may not be making a full connection)
3) Spark plug installation and gap
Make sure that a proper connection is being made in the spark plug boot. Inspect and/or replace the spark plug. Correct spark plug gap is 0.038″.
I’m not getting a spark at all!
1) Check your wiring connections
Double check the connection of the wires, particularly the blue to blue and black to black.
Check that no particles are lodged between the side and center electrodes of the spark plug.
Try replacing the spark plug or cleaning it by running sand paper through the side and center electrodes and resetting the gap to 0.038″.
Re-test for spark with the kill switch pressed in. Try feathering the kill switch. Disconnect the white wire completely allowing the wire to hang free, then re-test the engine.
If the connections are free and clean but you’re still not getting a spark, it’s time to test your components:
1) Magneto testing
Take a voltmeter or multi-meter and adjust it to the Ohms setting at 20k. Ohms measures the resistance across a circuit. Check voltmeter across the following wires:
- Blue wire to the White wire of the magneto. The resistance should be 0.25 to 0.40. New magnetos read 0.31.
- White wire to Black wire should read 0.0.
- Blue wire to Black wire should read close to 0.31.
- If your reading is far off from this, then the magneto is to blame for weak/no spark.
If the readings check out on your magneto, test your CDI
2) CDI testing
Run the voltmeter at the same 20k setting. Check voltmeter across the following wires:
- From the inside of the spark plug boot to the Black wire of the CDI. Your reading should measure 2.0 – 2.7. A new CDI will read 2.3.
- Spark Plug Boot to the Blue wire there should be no change, or 1.0.
- Blue wire to Black wire there should be no change, or 1.0.
- If the resistance is different than specified, this simple test will tell you where your problem lies.
Check out our spark troubleshooting guide video below: