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Cdi ignition module

woozybigfoot

CB750 Enthusiast
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I had a cdi ignition module blow out on me after replacing coil packs and wires.

Would the coil packs potentially be giving too much juice to the cdi module.

does the juice go from battery to the cdi then to coil packs the spark plugs....

Or does it go battery to coil packs to spark to cdi module
 
Battery to CDI to Coil Pack to Spark Plugs.
Purpose of the CDI is to boost the battery 12V to something higher. This then inputs a higher voltage into the coil pack, to give you a hotter spark.

How much hotter? Depends on the CDI, but maybe 10 times.
 
Battery to CDI to Coil Pack to Spark Plugs.
Purpose of the CDI is to boost the battery 12V to something higher. This then inputs a higher voltage into the coil pack, to give you a hotter spark.

How much hotter? Depends on the CDI, but maybe 10 times.
Okay so the failure of the cdi could have quite literally been just it's time to go then huh
 
It's not the CDI that is failing - it's probably the coil. CDI's don't boost voltage - coils do. However sometimes the coil and CDI are integrated so you have to replace both.
 
It's not the CDI that is failing - it's probably the coil. CDI's don't boost voltage - coils do. However sometimes the coil and CDI are integrated so you have to replace both.
Hey Cyber 104, Beg to differ slightly. Please see the following extract from a very good Wikipedia article on the history of CDI development. he term "Kettering" in the extract below is the technical name for the standard points and coil based ignition system.

"The discharge capacitor within the CD ignition had the ability to provide a powerful spark in excess of 4 times the spark power of the Kettering system using the same coil" (see https://en.wikipedia.org/wiki/Capacitor_discharge_ignition)
 
Agreed - it provides the spark simply by triggering the coil discharge - the coil generates the voltage. The CDI is simply the control unit. We can agree to disagree - I certainly don't profess to know everything - but for voltage/amperage change you need an inductive coil with primary and secondary windings.

The points system was simply collapsing the magnetic field and sending it to ground - the spark plug.

The CDI added an additional capacitor with an additional control - so yes - that capacitor stored voltage - but the base voltage and it's increase was caused by the windings in the coil
 
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I had a cdi ignition module blow out on me after replacing coil packs and wires.

Would the coil packs potentially be giving too much juice to the cdi module.

does the juice go from battery to the cdi then to coil packs the spark plugs....

Or does it go battery to coil packs to spark to cdi module
I have a 1980 CB750F and a 1982 CB900F that I have been messing with. They both had carb and ingnition issues that were driving me crazy. I fixed the carb issues with a set of Keihin CR carbs, expensive yes but they are better than the crazy complicated stock carbs. I was going to try the Murray set up but just not sure about having 1-2 and 3-4 on the same manifold. Seems some like them and some hate them.

On to ignition. I pulled the triger on a Dana 2000 and coils after having issues with stock style after market junk.
I pulled the tank off of the 900 getting ready to install the Dyna on that bike and I thought I would check the wires and coils with a meter.

1-4 23 ohms, 2-3 open!!!! Those coils and wires have less than a couple hundred miles on them. Ends up it was the cap that has a resistor in it and it’s the open component. Screw it I have a known good set on the 750 and since that’s the bike I am for sure going to keep it’s gona get the Dyna ignition.

Swap the coils and wires, drop the mains on the 900 to 110 and ride it. Runs fantastic.

After I installed the Dyna on the 750 I did more reading about these older stock ignition systems and found out a few more problems associated to these waste spark systems. Seems the wiring is kind of goofy in that, power comes from the battery through a starter relay and main fuse, into the headlight bucket, through the ignition switch, through the kill switch, to the ignition modules, to the coils and a lot of 42 year old connections.


I checked the battery voltage 12.5 then the voltage at the coils 11.4. That’s over a 1 volt drop! I know these ignition systems need good, clean voltage to opperate correct because the stator quit charging on the 900 a few months ago and it started to run real ratty. Rather than do voltage drops at each component I decided to install a relay that would switch straight battery voltage directly to the coils. Yep the 750 with the Dyna and 900 with stock ignition are both running great.

I recomend you check your charge rate, coil positve voltage and make sure your restiance for coil 1-4 and 2-3 is around 25 ohms just to check that box.
And I highly recoment a set of NGK DR8EIX Iridium spark plugs for these older CB's ignition systems.

As Cyber104 says the CDI unit is a control unit and it recieves a signal from the pick up on the crank shaft then send a signal to the igniton coil telling it when to fire. It does not build voltage. It is highly unlikely the coils damaged it.

Also understand that Wikipedia is crowd sourced information that is less than reliable.
 

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