Replacing a "Spark Unit" / "Igniter" / CDI (OKI MPS-200) on a '80 CB650

[roeme]

So since I apparently need to pose this question in different forums (a Honda-specific one was no help), I thought "surely the lot at GSResources is among the capable". So, here we go:

The bike in question is a '80 Honda CB650 (i think designated CB650Z in NA market), which – from what I could gather – sports a transistorized capacitor discharge ignition. So, it doesn't have points, just an inductive pickup, two of what Honda calls a "spark unit" and ignition coils. That's it. The spark units basically contain all the circuitry, and are marked as OKI MPS-200.

The circuits of these are potted, but apparently this potty (putty?) degrades after 40years in such a way that heat will make it runny, exposing the circuity (That is apparently a known problem, since a cursory google search reveals others having the same problem). And there's enough heat to go around; not only from the engine but also the units themselves do generate enough of it, apparently.

So I thought, "eh, CDI / transistorized ignitions must be a bog-standard thing by now", and sure enough, by searching for "6 pin DC CDI" you'll find dozens. They all seem if not the same, then just slight variations of a standard one. And judging by how they should be connected to the engine & rest of the ignition, and the MPS-200's schematic, those run-of-the-mill CDI's should be a drop-in replacement (well, needs some connector crimping) for the OKI one.

The only things I'm wondering at this point is firstly wether these units can handle the rpm's of a 4 in-line, since most of them are marketed towards the ATV/scooter crowd and often have something along the lines of "150-250 cc" in their title (It's my understanding however that an ignition doesn't care too much about your CC's). Secondly, I'm not sure how close the primary coil voltage needs to match...I suppose there's a bit of leeway, but I reckon if voltage of the new CDI is too low, I'll get a weak spark, too high, I might run the risk of frying the coils.

By any chance anyone of you already did something along these lines?

Here's a schematic of the original unit (the dashed rectangle) & ignition:

[salty_monk]

Something from these guys might work for you... https://www.ignitech.cz/en/vyrobky/tcip/tcip.htm

[Nessism]

Maybe a GM HEI module transplant?

http://gpzweb.s3-website-us-east-1.amazonaws.com/Ignition/GPZgmHEImod.html

BTW, that bike doesn't have a CDI. it's a transistorized ignition, which is different from a CDI

[roeme]

Thanks guys, you already helped me some steps along in this project. I'm reading up on the difference between TCI and CDI. So far from what I understand is that if I were to convert to CDI, I'd need to change the coils as well.

[LAB3]

Here's another possible source. The guys on the XS1100 forum have been asking "Has anyone tried this?" and I myself would like to know too. The XS's have a well documented problem of having the wires on the ignition pickup coils breaking due to stress on the wires caused by the movement of the mechanical advance mechanism. Used pickup coils have the same problem and any that are still in tact fetch a pretty penny.

https://www.elektronik-sachse.de/shopsystem-3/en/

[Grimly]

They certainly know how to charge, that's for sure.

[roeme]

Yeah, commercial digital ignitions are quite pricey (though one can find some knock-offs cheaper)...but I found the "speeduino" open source project, which let's you configure an arduino to replace basically almost any kind of ignition.

However, due to the EMI hell on a ICE you can't use a stock arduino, and that's where it gets pricey, due to the custom PCB's / Shielding / Input Protection / whathaveyou.

Currently it seems to me that I can either convert the whole ignition to CDI (so I could maybe keep the pickup), which necessitates a change of the coils as well, or buy some drop-in replacement which is very pricey.

(The GM HEI module would also require changing the coils – I have to check the prices to get this stuff on my continent, but that could be an option as well).

Will research further

[Grimly]

(The GM HEI module would also require changing the coils – I have to check the prices to get this stuff on my continent, but that could be an option as well).

Will research further

I built a GM HEI module a few years ago. It was running the standard coils perfectly well and giving nice fat sparks.
I meant to pursue it further, as some of the HEI units have an advance curve built in, but it being a pair of them meant trying to keep them in dead-nuts sync.
The older pickups with the mechanical advance takes care of that quite nicely.

[bitzz]

Most of those cheapo 6 pin CDI s for the Marelli scooters are AC and run directly off the stator, not rectified.
The problem with "car" ignitions is they either require a distributor or the firing order is wrong. There's a Dyna 6 box that has twin ignition, NOT CHEAP.

[roeme]

I owe you guys an update here. After some thinking I've decided to "re-pot" the units instead, since they worked fine the last time the bike ran. If that fails, I can get aftermarket ones from CSMNL for about 80 bucks a pop. Not exactly cheap, but neither too outlandish.

For posterity, here's what the units look like at the moment, i.e. how I found them:

[Rijko]

These guys offer a plug and play replacement for the OKI MPS-200 they claim improves several aspects.

Too bad they don't list a price.

https://www.marktronics.nl/CB650-MT1-S-Module-nl.html

Sorry, it's in Dutch, here's the Google translated version :

https://www-marktronics-nl.translate.goog/CB650-MT1-S-Module-nl.html?_x_tr_sl=nl&_x_tr_tl=en&_x_tr_hl=nl&_x_tr_ pto=wapp

[roeme]

Hey Rijko , that's actually what I was referring to with being available through CSMNL

[Rijko]

too bad ... i hoped to contribute a possible alternative ...

[Suzukian]

Looks like a melted Zener Diode in there. They are rated by watts and the "knee" voltage, as Zener diodes are put in backwards from regular diodes, and the resistance they give is what gives the voltage drop necessary to supply voltage. As long as you go bigger with wattage, it's the "knee' voltage that's important, and I would guess that's a 12 Volt system. Before giving up, I'd at least try replacing both Zener Diodes. I'd bet that the transistors are NPN, since one leg is going to ground. If you could find the value of the capacitors, you could make this "Black Box". Of course, that's always the hard part.

There's a used set on EBAY for $40 bucks.

https://www.ebay.com/itm/275880156561?hash=item403bbd1d91:g:7b4AAOSw9Y1kd8hb&amdata=enc%3AAQAIAAAA8MKF0bY04oayXCyctsQUqIWhI1E11%2Frwrkd8dzgmKQgH%2FCW2P8F5sKM4V7cQFSJAJeHNul547Ddls5JCT44RIY0nAoAOhH8vI%2Fr5hEQg0KObHTmJYSWZTtuqNlymmxllSEnSlYLaU%2BmSd0S7yKgMmPhE%2FwupS91OfwCeejwTq1LjE%2FmZOytEOfzW9ZfLECKhjKHq%2FCH%2FCHQDNLNRC9amA%2FADbQ9CW%2FD1Nd4B5up49I5bheh6n%2BnwMQDnvW6zAw2c4%2F7R4hMKBHPgNlQxT3dFVhwLmtAhIUbWSU5o%2B4m9yrl6Rl%2BMfZQOBUrBc90mHHcrtA%3D%3D%7Ctkp%3ABk9SR_yzkaGUYg

[roeme]

Suzukian; thanks - though I have to mention that the units are still working, or at least, they were before I got the bike. It's "just" the sealing putty/epoxy that has degraded after four decades. I will attempt to reseal them with new, heat resistant epoxy. If that fails, I will get aftermarket ones from CSMNL as mentioned. (The ones you've helpfully linked - thanks again - are unfortunately already sold - though I imagine the would suffer from the same issue anyway).