CDI question.

[stevo as b4]

Any electrical wizards able to give me some advice on a CDI conundrum?

Basically the KMX CDI is fed power by an ignition source coil built into the alternator windings. I assume this is like an electronic flywheel magneto style ignition. It also means as far as I can see that the bike should run without the battery connected.

However I want to order an aftermarket CDI and most of these are fed by the battery, so the ignition source coil would not be needed or connected then.

Apart from having to change the wiring to suit, is it likely to cause any problems to go to a dc fed CDI box and just leave the ignition source coil/magneto disconnected?

I don't think the power consumption of the CDI will be that high, but will my spark be ok if the coil was designed to work with a flywheel magneto/source coil and I fit a battery powered CDI?

[WD Forte]

Without knowing the bike or specs its hard to say for sure but generally,
AC CDIs have a coil with a primary windings and turn ratio
designed for higher voltages than a DC CDI or tranny ignition system which uses a nominal 12v on the primary.
It may work but best check with the vendor to see what coils they
recommend.

Isolating the source coil shouldn't do any harm to the rest of the bike
but depending on the bike, stator and source coil power.
I might consider using a dummy load to bleed off source coil power to ground.
might not be needed though
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bikers smell of wee

[stevo as b4]

Sorry the bike is a 1986 Kawasaki KMX 125. It uses a self generating CDI ignition set up. I'm after a programmable ignition system for it.

I think I need to do a bit more research on this before parting with
my cash.

In my mind there can only be benefits to a good Battery CDI set up, and once wired up correctly to suit, it's going to be a simple enough system too.

But saying all that on a kick start only bike, there's no need to worry about the current draw on the battery when starting, and people so say that flywheel magneto style ignition systems do tend to give a powerful spark and I guess as long as the stator/source coil is in good condition there's little that can go wrong?

I was really after a CDI box that would if possible plug and play with the old one, or at least allow me to just change connector plugs and wire in any different wires the new CDI might have.

For this reason maybe I should look for an electronic self generating ignition system or CDI that would work with one.

The HT coil issue is another thing that concerns me, as I'd want to use the same coil if possible, and my mind struggles to see how a coil that works with a flywheel magneto system would also work with 12v dc?

[WD Forte]

Ignitech do various programmable ignition units
that many guys with older CDI igntion CXs fitted
as changing stators meant an engine drop and the unique ( to the CX) CDI boxes were getting scarce.
and could fail with no warning
( I have the later, better TI system in mine)
Have a look but personally I wouldn't bother on a simple to fix bike like that
You could rewind the stator and source coils yourself quite easily and 1 cyl CDI boxes are cheap and easy to get hold of as many bikes use them.

The Sparker DC-CDI and DC-CDI-P ( programmable) are for 1 cyl machines
https://www.ignitech.cz/en/vyrobky
____________________
bikers smell of wee

[Robby]

Stevo, it looks like you're getting mixed up with the amount of power a CDI receives versus the power of the spark.

The relationship between an ignition controller (little black box) and ignition coil is a bit like the relationship between the starter button and the start motor. The little black box is there to tell the coils when to fire, not control the strength of that spark.

If you want to fit programmable ignition, the only bits you need to retain from the old setup are some kind of ignition pickup and the coil. Your new black box will handle the advance/retard based on what you tell it to do.

[redeem ouzzer]

Why do you want to put an aftermarket CDI on

A) a 125

B) a 125 that isn't electronically restricted?

It's not a KR1 or RGV where you can get massive increases in power or driveability by a custom map (does the kmx even have a proper servo driven power valve?).

[stevo as b4]

All good questions, will try to answer if I can.

1, Yeah it's only a 124cc, not that I see that as an issue really

2, Your right that my bike runs a mechanically driven power valve, so all the CDI needs to do is tell the plug when to spark for the appropriate engine speed.

3, Not even RGV250's gain masses of extra bhp at peak from a fully pogramable 2D or 3D ignition. You'd be lucky to get 2-3bhp more on those bikes, but the midrange increase is significant and so is the benefit of accurate adjustable power valve control at different speeds to what the factory CDI was pre-set to.

I have a load of new parts soon to be fitted to my KMX125, stuff like a bigger carb, reedblock, modified airbox lid, and a pipe as well. The new pipe will be a one off pipe that is custom built to suit the tune of the std engine.

The pipe builder needed a full ignition timing map from 1000-10000rpm, to get the data for the best possible pipe design. I could not supply this info despite enquiry's to KHI japan, and because I'm paying a lot of money for the pipe, I didn't want the design to be compromised for the sake of an ignition system

The new CDI will allow a custom ignition map to be made on the dyno to make the pipe work at it's best and give the most performance possible.

Lastly I have a re-conditioned 200cc big bore top end sat here that's been ported and had the head modified too, if the CDI does not do much on the 125cc, it will probably be more effective on the tuned 200cc kit when that goes on eventually. Obviously my new pipe will be useless then, but I'd like to do this in stages and run the bike as a 125 with all the aftermarket bits on first to see what it's like.

Anyway I'm surprised you ask why I'd like a new CDI, as your already aware even your X5 would probably gain something worthwhile from a programmable ignition, especially if you have non std pipes or any other mods fitted?

[redeem ouzzer]

Why would i waste money putting a Zeeltronic etc on an X5 when it's

A) Bog standard

B) The worlds simplest 2t?

The advantage of Zeel or Ignitec boxes is a bigger spark and the ability to map the powervalve opening (custom revs and progressive opening rather than just open or closed, plus you can add a hard or soft rev limiter and easy wire a quickshifter. Also you can add switchable maps so in theory you can have a "rain" button. It made such a difference to my mates KR1S in terms of driveability and torque he regards the bike as unrideable with the original CDI.

Then again I stick with points on my YR5 cause it doesn't rev high enough to cause issues, has bugger all torque anyway and the weight saving over CDI is more useful. This might change if i move to a set of hand made pipes however....

[stevo as b4]

The thing is that Id actually pay extra to have a mechanically driven power valve system on a two stroke bike. If it opens and closes at roughly the right rpm, then that's all it needs to do, and it's bloody simple and hard for it to spaz up and go wrong.

I think progressive power valve systems are a step too far on two strokes anyway. All you need is the bottom end boost from a power valve, and at the rpm point where the graphs from an open and closed power valve cross over, for it to open etc.

It does depend on what type of powervalve system is used too, but I think the RD350F would have been more exiting if it was a system where it snapped open and closed at a certain rpm, instead of a progressive opening?

I know I could save a lot of time and money if I forget about ignitions and tuning, but I'm committed to having my pipe built now and I've spent a load on a bike so far that I want to be buried with, as I'll never sell it for sentimental reasons.

I could take a leaf out of Carvel's book, and if some fool was stupid enough to buy all my KMX's engines, parts and spares, id have enough for an immaculate 98/99 Fireblade instead of messing with teenagers bikes.

The trouble is I guarantee that if I had a mint 98 Blade instead, id ride it no more often than the KMX, and it would be just another Sunday polishing bike more often than not, but without the nostalgia I get from my current bike.

[redeem ouzzer]

The standard YPVS system is either open or closed, as far as i'm aware no manufacturer bothered with a progressive system as standard. That's why a standard 350 YPVS does that horrible clucking thing if you try and cruise at 5500rpm.

[stevo as b4]

I've emailed the ignition system suppliers to try and get some more information and guidance.

I'm having a mental moment in that I'm confusing my different types of electronic ignition systems up, and trying to remember how the CDI system works.

I assume that ac CDI's will use a primary voltage of around 180-250v ac to energise the coil and the Capacitor too. If I wanted to move to a dc battery fed CDI box, I still struggle to see how a coil that expects 180v ac is going to work or be happy with a 12v dc feed, and the same with the capacitor too.

I think the answer will be to keep the system ac and get a programmable ac CDI, as it should then mean I can keep the existing ignition coil and not make any significant changes to the wiring.

I know the pick up coil does not matter, and that will give the same nominal voltage when used with an ac or dc system. But I don't want to change the coil and the primary wiring, as I'm trying to keep it simple?

[stevo as b4]

Right I've found out that the RD350YPVS uses an AC CDI ignition, with an ignition source coil built into the Alternator stator like my KMX does.

I think this is the kind of CDI that I would be best to get, as I can keep everything then, the pick up coil, source coil, and HT coil. The charging circuit should not be affected by changing the CDI box, and Zeeltronic and Ignitech make suitable units by the looks of it.

I'm thinking AC is the way forward, as I don't need a DC supply to drive the powervalve system, being mechanically operated.

Is there any good reason not to go for an AC system based on the above?

I've also heard that most AC CDI box's are smaller too, which is good because they don't need a transformer to step up the supply voltage to charge the capacitor.

[Islander]