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Join Date: Jan 2011
Location: Smack in the middle of Illinois
Thanked 291 Times in 286 Posts
The 400EX has AC excited ignition - it does not need a battery to run
Spark is killed by grounding the CDI - there is a black/white wire on the CDI box, connect it to ground (green wire) and the spark goes away
If disconnecting the b/w wire does not get the spark back, then the problem is in the ignition system - the ignition system consists of the spark plug, spark plug cap, coil, CDI box, stator, flywheel and the wiring connecting everything. 90% of all electrical problems are connection related and 90% of all bad connections are ground connections. After disconnecting the b/w wire, check all ignition related ground connections, then check all other connections then start checking components.