No Spark - 1983 GPZ/EX250 C

The backstory: I'm new to motorcycling, having only recently inherited a 1984 GPZ550 from my uncle. It's a wonderful bike and runs great. Too well, in fact. I wanted to improve my mechanical skills, so naturally when a 1983 GPZ250 (EX250-C on the VIN) non-starter went for sale near me I had to take the opportunity. The bike is in good condition for its age, the only real cause for concern the fact that it hadn't been started in 8 years. Compression is good, I bought a new battery and the starter turns over freely, but my problem is no spark. 

First I checked and cleaned the electrical connections, confirmed there were good grounds and replaced the spark plugs. No issues there. In order to test the electrical components I first had to hunt for the service manual for this particular model, as the 1983 model appears to first in the 250cc series to feature electronic ignition. The pdf manual for the KZ250 & 305 years 1979 – 1982 freely abounds online, but I had to find a physical copy of the manual which also covered the relevant1983 and subsequent supplements. I intend to unbound, scan and upload this manual to share with the internet hive-mind once this bike is up and running.

I followed the manual instructions and performed resistance tests for each of the components in the ignition circuit; pickup coils (which perform the spark timing from the crank shaft), exciter coils (which induce current from the crank shaft to charge up the CDI box capacitor), CDI box and ignition coils.While there’s a whole table of readings for the CDI box I can’t get a single sensible reading from my multi-meter. I borrowed a few better quality multi-meters to confirm it wasn’t just my cheap meter. The manual does say that only the “Kawasaki Hand Tester 57001-983” should be used to measure the various resistances of the CDI box, as other testers “may show different readings”, but I have no idea how or if one could even get access to that kind of thing anymore? Still, it’s a dubious result for the CDI box, but doesn’t rule out any options. 

As for the other components tested, I’ve compiled their specified resistance ranges and my test results below:

Pickup Coil – Range: 8.5-12.9kohm. Reading L: 12.4kohm. Reading R: 12.3kohm.
Exciter Coil (High Speed) – Range: 2.5-7.5ohm. Reading: 6ohm.
Exciter Coil (Low Speed) – Range: 2.7-4.1kohm. Reading: 3.3kohm.
Ignition Coil (Primary Winding) – Range: 0.18 – 0.28ohm. Reading L: 0.8ohm. Reading R: 1.4ohm.Ignition Coil (Secondary Winding) – Range: 3.2-4.8kohm. Reading L: 8.3kohm. Reading R: 8kohm.

To summarise; my Pickup coils are on the high side, but still in spec. The exciter coils are comfortably within spec. The Ignition coils are sadly well above spec, although the appear to be in good condition with minimal rust around the exposed iron core. The specified primary resistance range is also dubiously low. In my research I’ve haven’t been able to find any reference to such a low primary resistance for a coil.

Before I can attempt to draw conclusions and suggest possible next-steps, I have two more pieces of confounding information to share.

Firstly, during my initial optimistic attempts to try starting the bike with the carbies connected, after numerous unsuccessful attempts while feeding it mouthfuls of ‘Start-Ya-Bastard’ it did managed to start up and run for ~20-30 seconds on one occasion, and not again.

Secondly, while cleaning and testing the connections in the ignition circuit I observed the following strange behaviour: when I disconnected the wire supplying power from the CDI to one of the ignition coils I would get a bright and consistent spark from the opposite coil. When I reconnect the power to ignition coil I get a single spark and then nothing. This behaviour is consistent with either coil disconnected. 

I’m sorry to ramble on, but I hope this all helps to paint a picture. The behaviour suggests to me that either the capacitor in the CDI box is giving out and as a result is struggling to produce sufficient charge to power both ignition coils, or the CDI box is fine and that simply the increased resistance of the ignition coils is too much for the circuit to overcome. Maybe it’s a bit of both. 

Anyway, my question is; what next? 
I’ve found original coils on ebay, but I don’t particularly feel like blowing $200-$300AUD on 40yo coils that are quite likely not much better than my current ignition coils. Same deal with a replacement CDI. After lots of googling I’ve also managed to get a quote from a company called ‘Vectriq’ that claims to specialise in ECU repair. Still, that’s ~$200AUD to troubleshoot and tell me that my CDI is fine, or $400 to repair and still have dodgy ignition coils. 

I’d rather a cost-effective repair than maintaining authenticity, seeing as this is an under-represented and not particularly sought after model. Should I give up on trying to make the current ignition system work and throw it out in favour of replacing with a Dyna-S ignition? Another point of interest for those who’re still reading this far on; unlike all the other motorcycles I’ve looked at so far, the stator, pickup coils and ignition timing setup all sit in the engine oil. The oil seal is in the engine side cover which is removed to access these components. Is this a common configuration? Would a Dyna-S even work in this environment?

How are you testing for spark?

A bike that sat for eight years has clogged carburetors. They will need a complete tear down and will need all the orings and gaskets replaced. The metal bits rarely need replacing.

Be sure to fix the brakes before taking a ride.

Sorry, I wrote out my post in a word-editor, copied it across to the forum and didn't pick up that I'd somehow missed a big chunk of what I'd originally written. I've updated my original post now.

I'm testing for spark by grounding the spark plugs to the engine body. I've confirmed that plugs are gapped to spec, and as my updated post now says, I get can get consistent, observable spark for one plug/ignition coil at a time, so I know it's grounding properly.

Absolutely; read you loud and clear on carbs and brakes, that'll by my next adventure once I've got ignition working consistently...

Sorry, I originally typed up my post in MS Word, and didn't realize at first that most of it hadn't copied across properly. I've fixed it, and the missing info should now be there.

I'm testing for spark by grounding the spark plugs against the cylinder head. I've measure and confirmed my spark plugs are gapped properly, and the fact that I'm getting consistent spark on individual plugs/ignition coils means I must be testing right?

Absolutely, will need to give the carbies and brakes a lot of attention before its road ready, just trying to get past the first electrical hurdle.

ZachM wrote:

Sorry, I originally typed up my post in MS Word, and didn't realize at first that most of it hadn't copied across properly. I've fixed it, and the missing info should now be there.

I'm testing for spark by grounding the spark plugs against the cylinder head. I've measure and confirmed my spark plugs are gapped properly, and the fact that I'm getting consistent spark on individual plugs/ignition coils means I must be testing right?


 

So I'm confused, the post title says "no spark" but the above suggests you have a spark ??? what is the electrical issue ?

It’s an inline twin. When both ignition coils are connected to the CDI, as is required to run the bike, there’s no spark.
When I was investigating as to why, I noticed that when I disconnected one of the ignition the coils the other coil would then start sparking.
Does that make sense?

Each coil absolutely needs a good 12Volt power supply on one terminal, the other terminal gets "grounded" (per spark) by the ignitor, triggered by each pick-up coil.

Clean all terminals nicely, and also pay attention to the earth strap from the battery to the frame.
Simply measuring with a volt meter indicates battery "potential", but not necessarily the battery's ability to deliver current.
You will need to check that there is at least 10V on the coil's terminal while cranking, as the current drawn by the starter motor will drop the battery voltage to around 10 volts.

The handlebar mounted ignition "kill-switch" is a likely suspect as the 12V supply to each coil is "interrupted" by it.
The Ignition switch may also require contact cleaning, to ensure good current flow.

H.

I agree with Howard, I suspect there is a corroded connection in the coil supply which is breaking down with the extra load of both coils being connected. Use a voltmeter and follow the "resistance fault" process in my fault finding guide (link is in my signature)

Thanks Wookie and Howard for the solid advice. I'm afraid I've already cleaned, tested and confirmed continuity for all the terminals connections. No easy wins there sadly.
I wasn't as thorough with my ground checks. I'll do another pass before I completely rule out that possibility.

I'm afraid the '83 model is quite eccentric. There's only a single 'power' cable supplying the ignition coils from CDI, so the spark timing must be handled within the CDI. I can provide the manual's circuit diagram if that's helpful? The CDI is not connected to the battery or 12v power at all, but gets charged by the 'exciter' coils, which to my understanding are effectively the same as the stator coil which supplies charge to the battery. Following the service manuals recommended impedance check they've tested within the acceptable resistance range.
The sidestand and starter lockout safety switches are only introduced in the '84 model. I'll try and give the ignition switch contacts a clean, but there's no problem with the starter relay and starter motor turning over?

Honestly, my suspicion is that the problem is with the ignition coils. The specified impedance range in the manual for the ignition coil's primary circuit is incredibly low; 0.18 - 2.8 ohm. Both my coils have a measured resistance around 0.8 - 1 ohm. Could that explain why the power coming out of the CDI isn't enough to overcome the impedance for both coils?
If so, where can one purchase new ignition coils with such a specifically low impedance?

Will have a look later, the circuit diagram would be helpful

ZachM wrote:

Thanks Wookie and Howard for the solid advice. I'm afraid I've already cleaned, tested and confirmed continuity for all the terminals connections. No easy wins there sadly.
I wasn't as thorough with my ground checks. I'll do another pass before I completely rule out that possibility.


 

Looking at the diagram you posted the ignition system does appear "unconventional" so a circuit diagram would be very helpful. I would however draw you back to the highlighted text  above - "continuity" testing will not diagnose a resistance fault caused by corrosion etc (I don't know if you looked at my guide) an ohmmeter should only be used to test components which are isolated from their circuit, you cannot accurately test wiring this way. You should diagnose resistance faults with a voltmeter on a fully connected and activated circuit - the reason for this is checking continuity of a circuit with no load applied will not show a fault and will send you down a rabbit hole as you believe that part of the circuit has tested OK. If you took a piece of battery cable and cut through all but one strand of the wire it would still test as OK if checked with an ohmmeter as the meter measures resistance to flow of a tiny current from the meters internal battery which can pass through one strand. if you then connected it to a starter motor and activated the starter you would have battery voltage one side and maybe 2 or 3 volts after the cut because that much current can't flow through a single strand (until that strand melted)

 

Wookie - Wish I'd seen that cartoon explaining electric current 45 years ago, could have saved a lot of head scratching in electric theory class !