TOPIC:

Circuit Diagram attached. Hopefully that helps shed some light on the situation?

OK Zach, first thing is forget everything you may have seen in other posts about testing ignition circuits as everything is different with this set up. It's difficult to look at part numbers as it appears your bike is a Japanese "home market" only model so no info on CMNSL however it looks to use the same system as an 83 305. The ignition switch and kill switch are switching "Grounds" to the CDI module not "lives" like most of the bikes here. Also there is no ignition live to the coils, instead they have a permanent ground and the live is supplied as a high voltage discharge from the CDI when triggered by the pick ups (could be as high as 500v) this is also why the coil specs seem strange. Given that both coils will produce a spark when connected individually I suspect the pick-ups and the coils are functioning correctly, within the CDI module there is a series of "diodes" which split the capacitor output to the individual coils, I suspect the fault is inside the CDI which is sealed (if one of the diodes is down then the coils will wipe each other out when both are connected) Without the benefit of an oscilloscope it would be difficult to diagnose 100%. My best advice would be if all the wiring up to the CDI checks out correctly then it's most likely the CDI is faulty. I would suggest cross referencing any part numbers with the components you have

Hi all, sorry for the radio silence. It's been an incredibly busy Feb-March but I've finally managed to freed up some time to get stuck back into troubleshooting.

I heeded your advice Wookie, re-read your Fundamental Electrical Principles and Fault Diagnosis Guide, revisited and re-cleaned all of the electrical connections in the ignition circuit from the pickup and exciter coils all the way to the spark plugs, confirming that I have good contact at each connection. Unfortunately, it was not feasible to test under load, as the circuit is powered from the exciter/stator coil, which is powered is itself powered by the crankshaft and starter motor in turn, and I didn't particular want to try and burn out the starter motor.

Thanks for providing some insight into the nuance of what's happening inside the cdi box. I'm based in Australia, which might explain the difficulty with the model lookup. I can confirm that it is effectively the same system as the 1983 305. The relevant service manual suplement lumps the ER250-A1/B1, EX250-C1 (my particular model) and the EX305-A1/B1 together. From what I can tell it's the same bike, just with smaller cylinder bores.

My  concern with replacing or sending the cdi out for repair is that even if the CDI is operating perfectly well my original ignition coils have internal resistances 2-3 times greater than the maximum allowable spec, which I suspect would continue to contribute to my spark problems.
Is there a way to source such a niche specification of ignition coils without taking an absolute chance on an overpriced 40 year old set on ebay?

I can't help but think that at this point the most straightforward solution would rather be to give up on the white-elephant CDI/ignition coils and purchase an aftermarket digital ignition system, since I'm going to have to start throwing money at this anyway.

Or, to propose a crazy alternative: I have managed to scavenge a presumable working IC igniter (Part# 21119-1415) and ignition coils from a wrecked 1999 Kawasaki EX250-F9. Seeing as it's basically the same bike, but 16 years younger (Kawasaki 250cc 2-cylinder), and the wiring diagrams are highly accessible I imagine its as close to suitable as any other aftermarket replacement. Anyone with experience that can lend advice on how feasible this endeavor would actually be? Or is this a fools errand.

Web-bike have 0.2ohm coils 

 

ZachM wrote:

Hi all, sorry for the radio silence. It's been an incredibly busy Feb-March but I've finally managed to freed up some time to get stuck back into troubleshooting.

I heeded your advice Wookie, re-read your Fundamental Electrical Principles and Fault Diagnosis Guide, revisited and re-cleaned all of the electrical connections in the ignition circuit from the pickup and exciter coils all the way to the spark plugs, confirming that I have good contact at each connection. Unfortunately, it was not feasible to test under load, as the circuit is powered from the exciter/stator coil, which is powered is itself powered by the crankshaft and starter motor in turn, and I didn't particular want to try and burn out the starter motor.

Thanks for providing some insight into the nuance of what's happening inside the cdi box. I'm based in Australia, which might explain the difficulty with the model lookup. I can confirm that it is effectively the same system as the 1983 305. The relevant service manual suplement lumps the ER250-A1/B1, EX250-C1 (my particular model) and the EX305-A1/B1 together. From what I can tell it's the same bike, just with smaller cylinder bores.

My  concern with replacing or sending the cdi out for repair is that even if the CDI is operating perfectly well my original ignition coils have internal resistances 2-3 times greater than the maximum allowable spec, which I suspect would continue to contribute to my spark problems.
Is there a way to source such a niche specification of ignition coils without taking an absolute chance on an overpriced 40 year old set on ebay?

I can't help but think that at this point the most straightforward solution would rather be to give up on the white-elephant CDI/ignition coils and purchase an aftermarket digital ignition system, since I'm going to have to start throwing money at this anyway. Don't forget your ignition and kill switches are switching grounds to the CDI so would potentially be a lot of re-wiring to make something else work

Or, to propose a crazy alternative: I have managed to scavenge a presumable working IC igniter (Part# 21119-1415) and ignition coils from a wrecked 1999 Kawasaki EX250-F9. Seeing as it's basically the same bike, but 16 years younger (Kawasaki 250cc 2-cylinder), and the wiring diagrams are highly accessible I imagine its as close to suitable as any other aftermarket replacement. Anyone with experience that can lend advice on how feasible this endeavor would actually be? Or is this a fools errand. Share the wiring diagram and I will take a look, however remember on this type of ignition the "advance curve" is built into the igniter so even if viable may not perform as you want

Here is another option for coils