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Discussion Starter #1
Ok, I promised LT I would post up about what I'm working on. Maybe others can add their experiences and knowledge so that we can all learn more about these little burros. :icon_thumright:

What I'm doing here is really not very original. I've read about at least one other TW owner who made a Chinese CDI run on a TW, and even saw a video of a guy who did the same. However, these were '88-up TWs and mine is an '87.

There is a rumor going around that '87s use a DC powered CDI. I would like to dispel that right now. It is AC. In fact I think the only difference in the CDI supply stator as compared to the '88-'97? '00? whatever is an added section at the "bottom" of the stator that goes to ground. My understanding is that the '88+ needs to have the brown wire grounded before it will run on this CDI. The '87 will run without grounding the brown wire, because the winding is already grounded.

Before I go any further, the CDI I am using is a 6-wire AC CDI, made in China for GY6 clone scooters. I got mine for less than $10, shipped. Here is what it looks like:

 

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Discussion Starter #3
Here is how I connected it:
GY6 CDI TW harness
Green1-------------Black (ground)
Green2------------white (trigger)
Black--------------Black/white (kill) (main switch only; not the handlebar kill switch)
Red---------------red (CDI power)
Yellow------------orange (coil primary)
Blue--------------green (trigger)

The brown, blue, blue/yellow wires from the harness are not connected.
 
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Discussion Starter #4
It runs, but is obviously retarded. I can putt around at a moderate speed, but it is lacking in power and cuts out above (I'm guessing) 3500 rpm. Since it is retarded, it will also run hot if you try to get much power out of it. But this could still work as a limp-home mode if your stock CDI fails.

I'm not stopping there, though.
 
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Discussion Starter #5 (Edited)
Ok, so I checked the two green wires from the CDI (ohm and diode check) and they are both connected directly to ground on the board. So not only the supply winding, but also the trigger are referenced to chassis ground. As mentioned, the original CDI has one end of the supply winding near ground, but isolated from it by a small winding. Also, the trigger is not referenced to ground (as far as I can tell thus far) in the original. This could and probably does affect the timing. It's not anything insurmountable, though.
 
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Discussion Starter #6
I tried a little experiment of switching the two trigger wires so that the green wire from the trigger would go to ground, instead of the white. It kicked back but did not start, so that obviously changes the timing. I don't want to take that any further without having a better idea of what the resultant timing is.

Btw, I have changed the connectors on my original CDI so I can still connect it into the circuit. I eliminated the blue and blue/yellow safety circuits on the bike, and connected the blue/yellow wire from the CDI directly to the black (ground) wire from the CDI, because the blue/yellow must be grounded for the bike to run with the original CDI. I left the solid blue disconnected.
I had already connected it that way before I changed the connectors so I could use different CDIs, and it ran exactly as before: perfectly, except when the CDI was acting up.

I have an original Honda CDI from an XR100. I don't know if it is even any good, but I plan to try it. It has 5 wires. Those wires correspond to the GY6 CDI connection points, except that the GY6 CDI has an extra ground wire. It should work, and the Honda CDI has an advance curve that is reasonably similar to the TW CDI. Those are also available as cheap Chinese CDIs, and I have one on the Chinese 125 in my XL70. Runs great in that app, so maybe it can on a TW too.
 
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:DVery good Sir and thank you. This could help a lot of folks. I wonder if Sebastian (macbig2k1) would have any info on this??
 
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Wescog..... I know I appreciate your research on this subject, as well as others. I wonder what goes wrong with these cdi units. Can they be opened up and repaired? Or is this a "wound" unit like an electric motor? I know they can be rewound, so I don't know why the cdi can't be repaired. It pisses me off that so many of the parts we use on our bikes, cars, mowers, etc. are throwaway parts, but it makes me mad that these things are so expensive, and seemingly can't be repaired. Rant over, thanks for listening.
 
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Discussion Starter #9
I am hoping there are some members out there who have info, and will chime in. :icon_thumright:
 
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Discussion Starter #10
Wescog..... I know I appreciate your research on this subject, as well as others. I wonder what goes wrong with these cdi units. Can they be opened up and repaired? Or is this a "wound" unit like an electric motor? I know they can be rewound, so I don't know why the cdi can't be repaired. It pisses me off that so many of the parts we use on our bikes, cars, mowers, etc. are throwaway parts, but it makes me mad that these things are so expensive, and seemingly can't be repaired. Rant over, thanks for listening.
They can be repaired. Usually just some bad solder joints that need to be resoldered. It's a hassle to dig them out, though.
If/when I dig mine out, I plan to make a schematic of the circuit and also eliminate both blue wires altogether.
 

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Discussion Starter #11
Btw, in case anyone is wondering I have never dug out a TW CDI, but I have dug out a few other CDIs.
A basic CDI is actually very simple. Just a rectifier to change AC from the stator to DC, a capacitor to store the charge, and an SCR (latching electronic switch) to dump the charge into the coil primary when it receives a trigger signal. That term "latching" just means that once it receives a trigger pulse to the gate, the switch stays on until it dumps the entire charge from the capacitor.

The timing circuit is a bit more complicated, but not necessarily a lot more. Some designs are very complicated, but some are quite simple.

Another thing: I've seen some comments about using a DC CDI to simplify things. That can be a decent backup system to get you out of the woods if the stator fails or just to make the bike rideable while waiting for a new or rewound stator to arrive, but I am much more partial to an AC system for a long-term solution. A CDI needs somewhere around 200 volts, and a DC CDI has a built-in inverter to supply that voltage. The inverter adds inefficiency, hence heat. It is also by far the most likely part of the inverter to fail. If a DC CDI fails, it is a near-certainty that the inverter is what failed.

If that gives you the idea that DC CDIs are much more likely to fail than AC CDIs, you've got the right idea.
 

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Nice info bro, thanks. :D

This probably should be added to the technical section as a sticky if it progresses to a total solution.
 
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Discussion Starter #13
Nice info bro, thanks. :D

This probably should be added to the technical section as a sticky if it progresses to a total solution.
Sounds good to me, LT! I'm hoping it will lead to a total solution. It might require mods that preclude going back to the original CDI, but if it only costs $50 and a couple hours' time, it would be worth it.
 
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Sounds good to me, LT! I'm hoping it will lead to a total solution. It might require mods that preclude going back to the original CDI, but if it only costs $50 and a couple hours' time, it would be worth it.
I know, and any other 87 owner knows, how hard it can be to find good information on testing or even buying the CDI's. They are so expensive if you have one fail. Bro, your efforts and experimentation on finding a solution are very much appreciated. Continue on, and good luck bro. You have some good skills too. Thank You!! :D
 

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hello wecsog

i have been running my 1990 on a 10deg btc fixed timing chinese cdi for over a year now. it does knock the power back about 20% at highway speed but it does not cut out as you mentioned with yours so that is probably something else.

the bike does not run hot because of it and the valves look/seem fine. i'm satisfied that it's not hurting the engine. these are reletively low rpm engines and manufactures (including the tw200) often use radical retardation to limit rpms. check out the timing graphhttp://tw200forum.com/forum/attachments/technical-help/10499d1412905836-cdi-baseline-info-wires-waveforms-timings-substitution-tw-timingcurve.png for the tw.

(on my 90) the blue wire provides a path to ground (via the cdi and the blu/yell to the kill switch) for the e start interlock relay. does not affect cdi operation.

the pulsar/trigger is the same across all years (elctrically). yes as you mentioned, in the stock setup both wires go to the cdi, are not referenced to ground except perhaps in the cdi. with the universal cdi's one side gets tagged to ground. yes swapping the polarity changes the timing.

the stator should be grounded via black only. the brown wire from the stator should not be grounded, that effectively shorts out the winding from ground to brown. on mine brown is just isolated and not connected. ground and red feed the cdi.

i think the 87' cdi and stator are pretty well the same electrically as later models. they changed a bit of the interlock crap i think that is the main difference.

i did the same as you, put in connectors to be able to patch in varios cdi's.

you may have already seen it, but

http://tw200forum.com/forum/technical-help/11545-cdi-baseline-info-wires-waveforms-timings-substitution-3.html

is the most extensive online info on the tw cdi i am aware of. needs to be distilled, and extended to other years but there is core info there that crosses into all the tw's. there's a useful cdi-hookup wiring diagramhttp://tw200forum.com/forum/attachments/technical-help/8278d1406068683-cdi-baseline-info-wires-waveforms-timings-substitution-tw_cdi-diagram_v1.0.jpg.

slowmod
 

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Discussion Starter #17
Thanks for chiming in, slowmod. That's some good information! :icon_thumright:

Do you know of anyone who has tried the gy6 CDIs with adjustable timing?
 
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