How to Integrate a CDI Ignition with a mo.Unit

CDI ignitions are not inherently compatible with the m.Unit bur a simple workaround will allow you to integrate the ignition system so that it functions similarly to other ignitions. 

TO ALL THE VINTAGE HONDA PEOPLE. Before you decide to skip over the wordy bit to the diagram hear me out. 70-80's Honda street bikes very rarely ever have CDI ignitions, one exception being a couple of years of CX500. However, Honda diagrams and manuals frequently refer to the Transistorized Ignition Modules as CDI's. FOLLOW OUR INSTRUCTIONS before you spend the money on the components to make this modification. 

What exactly is a CDI? 

The acronym CDI has become a catch-all term for any black ignition module but stands for Capacitive Discharge Ignition, and a true CDI ignition module is fundamentally different than any other ignition module and as such it operates at a different voltage than the rest of the electrical system and is frequently self-excited, which means it will run without any battery in the bike. These are most common on off-road bikes, and a few of the smaller Japanese bikes from the 80’s and 90’s. 

How do I determine if I have a CDI? 

I encourage you to read this and attempt to follow the instructions below. If you email us asking us if you have a CDI we are going to do exactly what we outline here. 

The easiest way to determine if you have a CDI is to look at your OEM wiring diagram and locate the kill switch. Once you've found it trace each wire leading away from it, there will likely just be two. One of them will go to the ignition module, the other wire will go to ground. The ground is the key, When the kill switch is activated it completes a circuit that grounds out the CDI killing the ignition spark. In other words, if your Kill switch completes a ground circuit you have a CDI ignition. 

In other types of ignitions, the OEM kill switch when activated will break the 12v+ power circuit to the ignition system cutting ignition spark. 

The Revival Solution

If you think about how the m-Unit outputs work it becomes clear why a CDI will not work here, the Ignition Out provides 12v+ power which the CDI does not require. But by using a common 5 pole, normally closed relay we can make this work just like any other ignition. When the m-Unit provides power to the Ignition Output the relay opens the switched circuit. When the Kill Switch is activated the m-Unit cuts power to the relay, in turn, closing the switched circuit, grounding the CDI and eliminating ignition spark. 

We offer a quality Hella Waterproof Relay perfect for this application on our site. 

Click the image to view the entire PDF.

mo.Unit CDI Diagram

1 comment


    This info was really helpful when wiring up my Rotax 600 flat tracker. Thans.

Leave a comment

Please note, comments must be approved before they are published