swaping a cdi

5 replies to this topic
  • drewbbie

Posted August 30, 2010 - 07:16 PM


my buddy has a o3 yzf 450 hes haveing all kinds of odd ishues with it not starting and boging out when running we have figerd out iits the coil or cdi.
i have a 08 wr450 my ? is will the coil and cdi swap over? just to test it to see what exactly it is.

  • grayracer513

Posted August 30, 2010 - 07:19 PM


Nope. Way different.

  • drewbbie

Posted August 30, 2010 - 08:34 PM


coil too?

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  • grayracer513

Posted August 31, 2010 - 06:46 AM


The coil should be the same. CDI's aren't even close.

  • drewbbie

Posted August 31, 2010 - 08:46 PM


so today we tryd it and it fired right up now my ? is the spark plug cap is that the coil my buddy whos a honda mechanic sayd that its just a secondary coil and the primary coil is in with the magnito is this true?

  • grayracer513

Posted September 01, 2010 - 06:32 AM


No. The main energy source is in the magneto, but the coil cap is a typical high tension spark coil in miniature. In order for a spark coil to raise a relatively low voltage to the 20,000+ necessary for a spark plug, there have to be two coils, a primary and a secondary. A low voltage, but fairly high amperage current is supplied to the primary, which builds a magnetic field around it and around the adjacent secondary windings. When current stops flowing in the primary, the field collapses around both coils, inducing a high voltage, low amperage current in the secondary.

If the two coils are not physically close enough for the magnetic field from the primary to envelop the secondary windings, there will be no step up in voltage. If the CDI were to supply a voltage high enough for the spark, there would be no reason to have a coil outside of it. Your buddy is incorrect.

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