CDI and coil interchangability?

Discussion specific to the various air-cooled KDX models sold in the USA
bob_jones
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CDI and coil interchangability?

Post by bob_jones »

I searched and didn't find if this has been done.... Has anyone here actually tried swapping CDI and / or coil from E or H series onto C series? If so, what was the result? Does anyone have any information as to why this would or wouldn't work? Risks? Pros / cons? Thanks!
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Re: CDI and coil interchangability?

Post by Jaguar »

the E and H CDIs don't rely on a pickup coil as timing reference. Make sure your C is the same.
I would guess the swap would work but i don't know anyone who's done it. I've sold my adjustable CDI to someone with a 1982 kdx 175 before. I don't know what series that is.
ignition timing
E series: 21BTDC at 6K RPM
H series: 19BTDC at 6K RPM
Performance CDI -- KDX motocross mods -- the SR KDX -- expansion chamber analysis---> http://www.dragonfly75.com/moto/
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Re: CDI and coil interchangability?

Post by BillyWillicker »

If there are 3 wires coming from the stator it will work.
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Re: CDI and coil interchangability?

Post by bob_jones »

Jaguar wrote:the E and H CDIs don't rely on a pickup coil as timing reference. Make sure your C is the same.
I would guess the swap would work but i don't know anyone who's done it. I've sold my adjustable CDI to someone with a 1982 kdx 175 before. I don't know what series that is.
ignition timing
E series: 21BTDC at 6K RPM
H series: 19BTDC at 6K RPM
My 1986 kdx 200 c1 manual says ignition timing is 19° BTDC @6k RPM. Therefore, in theory, the H series CDI should be a direct match amiright?
Last edited by bob_jones on 09:56 pm Mar 12 2017, edited 1 time in total.
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Re: CDI and coil interchangability?

Post by Hail seizure »

A pick up coil is normally a little coil mounted outside of the rotor or sometimes on top of the source coil. My 88 C3 has no pick up coil to speak of either, anyone explain how the system works? Also what stator mod did you do to fit a later rotor?
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Re: CDI and coil interchangability?

Post by bob_jones »

I rotated the stator by cutting new slots and installed an H series rotor
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Re: CDI and coil interchangability?

Post by KDXGarage »

You did this on your 1986, bob_jones?
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Re: CDI and coil interchangability?

Post by bob_jones »

I did.
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Re: CDI and coil interchangability?

Post by KDXGarage »

Did you just trial and error to find the right timing or base it on the 1986 or what??
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Re: CDI and coil interchangability?

Post by bob_jones »

Trial and error but I started with the pics from the threads on here. At first my slots were too short and my timing was WAAAAAY to far advance. Then too retarded, and so on
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Re: CDI and coil interchangability?

Post by bob_jones »

[album] [/album]
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Re: CDI and coil interchangability?

Post by KDXGarage »

Ah, protractor!
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Re: CDI and coil interchangability?

Post by bob_jones »

Yep. My new timing mark is at TDC in the pic. BTW the timing mark on the H flywheel matches up with the mark on the case at TDC.
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Re: CDI and coil interchangability?

Post by bob_jones »

Jaguar wrote:the E and H CDIs don't rely on a pickup coil as timing reference. Make sure your C is the same.
I would guess the swap would work but i don't know anyone who's done it. I've sold my adjustable CDI to someone with a 1982 kdx 175 before. I don't know what series that is.
ignition timing
E series: 21BTDC at 6K RPM
H series: 19BTDC at 6K RPM
So riddle me this... from reading on here I keep seeing that none of the C, E, or H series use a pickup coil. I read on here that the voltage output from the generator tells the CDI when to fire. Is it conceivable that turning the stator for the C-series flywheel to E/H series flywheel mod doesn't require cutting new slots at all? Is it conceivable that it doesn't matter where the stator is turned? Turning the stator effects timing but how? and to what extent? What the hell kind of sorcery is going on inside there?
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Re: CDI and coil interchangability?

Post by Hail seizure »

I have just modded my stator but couldn't slot the right hand side as much as yours.
There is a little steel bracket at approx. 5 o'clock on my stator. In the stator pictured it is
at approx. 7 o'clock. Did you move your steel bracket to allow the slot to be made?
I have a H series flywheel on the way, so will try it in std position first.

Thanks Mike.
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Re: CDI and coil interchangability?

Post by bob_jones »

Disclaimer: I recommend that everyone purchase a modded stator from Fredette Racing Products. That is the only way to guarantee that it is done properly. I am not expert on this modification and I take no responsibility for the outcome of any of this. You should use Fredette. I should use Fredette. We all should use Fredette!

That being said...
I didn't move the little thing that sticks out on the side. I did rotate the thing that holds the wire on the back. I loosened the screw and flipped the holder so that the wire was slightly closer to the new place where it will exit the case. There was excess wire pressed in behind the stator.
I'm not sure what you mean that you could not slot the right side as much. Those slots need to be at least as big as the oem slots. You can't set yours exactly the same as mine. Maybe close but not exact. Therefore you have to have some room with those slots.
Case in point, last week my stator finally went out completely. I order a c-series 85watt from Ricky Stator and modded it again the same way as the one in the pic. I made a timing mark in the same position but I don't think the bike likes it. It seems like I don't have bottom end power like before and there is a noticeable knocking when the engine lugs hard. I retarded it several degrees and it seems to have helped. I'm going to retard again and see if that helps again. Therefore there has to be some size to those slots.
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Re: CDI and coil interchangability?

Post by bob_jones »

I just looked at your posts and I see that you said your setup is non-standard or perhaps different than mine. Please understand that I know nothing of any differences I what you have or any differences in the UK version or the SR version or whatever. I see you said yours has a pickup coil which would mean it's completely different. Please don't assume that my mod will work for your bike.
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CDI and coil interchangability?

Post by Hail seizure »

Hi thanks for the info! I am reverting back to the stock stator from my current set up.
Suzuki PE flywheel and unknown stator!
I will post a pic later showing what slots I've cut into my stator.
I think I can get the 90 degree adjustment with the cuts I've made.
Just waiting on delivery of my H series flywheel, E CDI and CR250 Coil!

Thanks Mike.
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Re: CDI and coil interchangability?

Post by bob_jones »

What was the outcome?
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CDI and coil interchangability?

Post by Hail seizure »

Hi, I've fitted all the new parts but can't get it to run yet.
It keeps kicking back as if timing is out.
Just a quick question first which may help me massively.
In the picture you posted with the protractor, is that how your
stator is mounted on the bike? ie is 0 deg TDC?
Or is the 90 deg TDC?
What I'm trying to say is what orientation are your coils at?
The std set up had the source coil at the top almost horizontal
and the lighting coil 180 opposite. How is yours mounted?
Any pics? Thanks Mike.
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