CDI Coil Fly Back ?

[Scoobysruvenge]

I have an 08 Kawasaki KLR650 Sinle Cylinder engine I have purchased a Microsquirt controller for a fuel only application. I will add the timimg later.

I have most everything wired and am ready to get the tach signal to the MS... But after reading the fuel only section I found that CDI coils and MS don't mix.

I however I see a CDI coil for sale on the DIY/MS site listed as having the primary and secondary coils separated unlike most OEM CDI coils.

“Here's a race coil designed for CDI applications that's small enough and cheap enough to use one per cylinder if you're so inclined. These are vibration resistant and can be mounted at any angle - no oil to leak out. Also works with capacitive discharge ignition boxes - MSD, Mallory Hyfire, etc - if you're using a distributor. While many CDI coils have just two connections, this is one of the few CDI coils you'll find in this price range to add a secondary ground connection to isolate the primary side from the secondary. It uses standard HEI type spark plug wire boots.

A - "Positive" terminal, wire to the terminal on a CDI box used for coil positive
B - "Negative" terminal, wire to the terminal on a CDI box used for coil negative
C - Secondary ground, connect to cylinder head.”

Why would MS sell a CDI coil if they do not support CDI coils with the MS controller. I suspect swapping my OEM coil for the MS Coil will get me where I need to be can anyone help here?

Thanks for your interest.

[dontz125]

CDI coils work with MS and uS if 1) you have a CDI driver and 2) a trigger wheel of some sort, whether missing tooth, points, dizzy, etc. Also, the CDI coil doesn't generate the same flyback pulse that an inductive (TCI / points) coil; with TCI, the energy is built up in the coil then released when the field collapses. With CDI, the energy is stored in the capacitor, and very little is available as a trigger pulse, Finally, you really don't want to connect your uS to 250-400v ...

Long story short - a uS can neither drive nor be driven by a CDI coil, without additional components.

[Matt Cramer]

Why would MS sell a CDI coil if they do not support CDI coils with the MS controller.

They are for installations where you drive them with an external ignition box like an MSD 6A or an M&W. Lots of people trigger these from a MegaSquirt. As Don explained, CDI modules don't send a signal to the coil that is very usable as an RPM signal. Some of them even spark multiple times per ignition event (I have no idea if the KLR650 does this or not), which would really throw things off.

The best tach signal source would either be a tach output on the CDI module or the pickup that triggers the CDI.