Motorcycle CDI info Technical

[Steve and Denise]

Is there any one out there can explain the advance curve on a CDI system with no mechanical advance ie crank triggered.
I have been told by makers that it is built in the box to advance but when a strobe is connected and RPM increased the timing marks stay in the same place on this particular system.

These are after market units we have been playing with fitted to a twin set at 10deg btdc and should advance in incements to around 38deg when rpm is increased max 7500 rpm.

Some of you racer boys may have some knowlage on this unfortunatley mine is a bit out of date ie points and mags.

 

[Jaws]

If the strobe is staying static then the timing is not changing ..
I have seen some CDI's that have USB socket to change the programming ..
It is not one of those is it ?

 

[hilldweller]

Is there any one out there can explain the advance curve on a CDI system with no mechanical advance ie crank triggered.

CDI - Capacitor Discharge Ignition was the next step up from points in the 1960s but was still actually triggered by points.

Do you full blown electronic ignition ? There should be a small computer in there with a stored advance curve. Something like 10,10,11,11,12,12,13,.......37,37,38 the computer can work out the revs by timing two crank pulses, it then says rev 3000 requires table[10], finds table 10 is set at 22 degrees and it uses that to calculate when the next spark is needed. Normally you would be able to load the table to suit the motor and fine tune it.

 

[Steve and Denise]

No John
The supplier said it is programable but the only thing it seems to do is advance the static as most crank trigger pickups are fixed.

The only thing I have come up with from my understanding is to create a longer duration spark but am getting near the end of my limited knowlage.

@hilldweller Yes it is full electronic I understand what you say and dose that mean it moniters rpm ie tacho then advancers at different stages with the increase of rpm.

 

[hilldweller]

@hilldweller Yes it is full electronic I understand what you say and dose that mean it moniters rpm ie tacho then advancers at different stages with the increase of rpm.

I don't know what it is supposed to do, just what I would expect it to.

It has a static pickup from which it knows crank position and from two pulses it works out rpm, from those two figures it can time suitable delays for any number of sparks. As I said I would expect it to have an advance curve table to work off. You may or may not be given a program or method to edit that advance curve.

Have you got a link to it, that might give us some more clues.

^{_{Subscribers  do not see these advertisements}}

 

[Gorse Hill]

CDI - Capacitor Discharge Ignition was the next step up from points in the 1960s but was still actually triggered by points.

Do you full blown electronic ignition ? There should be a small computer in there with a stored advance curve. Something like 10,10,11,11,12,12,13,.......37,37,38 the computer can work out the revs by timing two crank pulses, it then says rev 3000 requires table[10], finds table 10 is set at 22 degrees and it uses that to calculate when the next spark is needed. Normally you would be able to load the table to suit the motor and fine tune it.

I've told you before your to clever for this forum Brian, there you go again showing off

 

[Steve and Denise]

Thanks Brian
I Knew some one one here would understand or relate to where I was coming from a good friend of mine has had more involvement in this than me but he thought he had it wrong when all the suppliers could not supply the info requested. As I stated all the (cdi) supplied were from china etc so maybe look at a better product but it is hard to find a supplier that knows what they are selling.

Thanks for your input I will keep you up to date once I have more info

 

[Jaws]

CDI - Capacitor Discharge Ignition was the next step up from points in the 1960s but was still actually triggered by points.

Do you full blown electronic ignition ? There should be a small computer in there with a stored advance curve. Something like 10,10,11,11,12,12,13,.......37,37,38 the computer can work out the revs by timing two crank pulses, it then says rev 3000 requires table[10], finds table 10 is set at 22 degrees and it uses that to calculate when the next spark is needed. Normally you would be able to load the table to suit the motor and fine tune it.

Gotta argue the point ( get it ! )
All carb Birds have a CDI, all little scoots had CDI ( many still have CDI though many have moved on to ECU type CDI).. CDI is triggered by a pulse from the pick up, not points.. sorry !

 

[Jaws]

Forgot... It may be possible to extend a spark by a micro second by making it fatter, but the sort of time you are talking about required to get a 38° advance is just not on

 

[hilldweller]

Gotta argue the point ( get it ! )
All carb Birds have a CDI, all little scoots had CDI ( many still have CDI though many have moved on to ECU type CDI).. CDI is triggered by a pulse from the pick up, not points.. sorry !

Kids today, know nuffin.

When I were a lad in the land of points, new technology introduced Capacitor Discharge Ignition. This replaced the normal 12V coil with a HV transformer, circuit that charged up a capacitor to a high voltage ( 100/200V ) and a solid state switch ( SCR ) that was triggered by the points which now switched next to nothing and never needed cleaning and setting.

Looks like the CDI mnemonic was good for sales and it carried on into full electronic ignition.

Never mind Blackbird, the Benley was the hottest Honda in the UK in those days.

^{_{Subscribers  do not see these advertisements}}

 

[Steve and Denise]

Still is Brian some old folks just do not realise it though.

 

[Jaws]

Kids today, know nuffin.

When I were a lad in the land of points, new technology introduced Capacitor Discharge Ignition. This replaced the normal 12V coil with a HV transformer, circuit that charged up a capacitor to a high voltage ( 100/200V ) and a solid state switch ( SCR ) that was triggered by the points which now switched next to nothing and never needed cleaning and setting.

Looks like the CDI mnemonic was good for sales and it carried on into full electronic ignition.

Never mind Blackbird, the Benley was the hottest Honda in the UK in those days.

Points driven CDI units lasted about 2 years Brian !! They soon dropped the points idea and used Hall effect switching

 

[Steve and Denise]

Now waiting for a unit from a Honda Transalp when it arrives it can be fitted and look at the results.

 

[PhilG]

What are you trying to do with it ??

 

[tonyidle]

Points driven CDI units lasted about 2 years Brian !! They soon dropped the points idea and used Hall effect switching

They also dropped CDI pretty quickly too (aftermarket for cars) because the short spark didn't suit everything. I built the Practical Wireless kit - anyone else?

^{_{Subscribers  do not see these advertisements}}