2000 YZ 426 ignition

4 replies to this topic
  • Old Thumper Driver

Posted June 07, 2014 - 11:52 AM


I am replacing the lower casings on the bike. My question is, when it's all back together, how does the CDI know when to fire the plug? I see the sensor next to the flywheel and assume that is where the signal comes from but the flywheel rotates twice for each time the plug should fire. How does it know which time to trigger the spark?

  • nuity5

Posted June 07, 2014 - 12:20 PM


I'm assuming it's like a lot of other motorcycles in the fact it does fire the plug every revolution of the crank. However one spark is on the compression stroke and the other spark is on the exhaust stroke and is "wasted" which is why this system is sometimes called wasted spark. Clay

Edited by nuity5, June 07, 2014 - 12:21 PM.

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  • Old Thumper Driver

Posted June 07, 2014 - 02:43 PM


Thanks, Nuity5. I never would have thought of that. Old school is hard to shake. My other dirt bike still has points and two rear shocks.

  • nuity5

Posted June 07, 2014 - 02:58 PM


Depending on where the points are located they can do the same thing. Only bikes that have points located on the camshaft (I had an old XL100 like this) would not have the wasted spark situation. If they're on the crank there is no difference than the magnetic pickup / cdi setup. Clay

  • Old Thumper Driver

Posted June 07, 2014 - 05:08 PM


Yep. The old one is a '76 TT500 and its point set is on the right case, with a reduction gear between it and the main drive gear. Thanks again.

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