81 GS450T no spark woes

[Guest]

Hey guys. I’ve got an 81 GS450T that, up until recently, was my daily rider. I took it off the road a few weeks ago to replace the chain (between waiting on parts and finding the time). After I got the chain on and adjusted, it fired right up and I rode it out of the garage. I got about 3 blocks from home and it quit (during light acceleration in 3rd). Since then, it cranks great but no start at all. Walked it back home, parked it for another couple days and today I finally got some time to dig into the problem. I’ve got no spark on either cylinder. I ohms-tested both coils and I’m getting readings in spec on the primary and secondary sides. I’ve got battery voltage at my coils, and my cheapy multimeter reads about 0.5V on the ground side while cranking (I assume it’s reading some sort of pulse there). Still no spark. I had some concern about the ground connection at my CDI/igniter so I double checked that and I’ve got very little resistance to battery ground. The stator was replaced by the previous owner about 6 months ago and I replaced the battery about a month ago. I’ve got the tank & seat off and it appears my wiring is good. Is it safe to condemn the CDI at this point, or should I venture down a different route? Thanks for reading and thanks in advance for your help!

[Nessism]

It's most likely the ignitor. A failed voltage regulator, or bad ground, often damages them from too much voltage. A Dyna S ignition is the expedient repair.

[Ktsteuart]

It's most likely the ignitor. A failed voltage regulator, or bad ground, often damages them from too much voltage. A Dyna S ignition is the expedient repair.

Is it normal for an igniter to just take a dump like that? Even though I rode it a few blocks?
I’ll try and test the voltage regulator tomorrow but if a bad ground can kill it, I’m betting that’s the case.

[Nessism]

A bad ground for the R/R causes the unit to malfunction and the voltage from the charging system can spike up to something like 17 VDC, and that can kill the ignitor. Don't know if this is what happened, but I do know the R/R ground on the 450 is horrible and ignitor failure is very common on that model.

[tom203]

Have a look at signal coils behind that little round cover lower right side, in case a wire got pinched and is grounding out

[John Park]

A bad ground for the R/R causes the unit to malfunction and the voltage from the charging system can spike up to something like 17 VDC, and that can kill the ignitor. Don't know if this is what happened, but I do know the R/R ground on the 450 is horrible and ignitor failure is very common on that model.

Which makes used replacements scarce and expensive, unless you get lucky. '83 on bikes had electronic advance and a fixed rotor; you can swap in a GS500 system which is far more plentiful used and seems more inherently robust. You will have to splice the connector plug into your wiring which isn't difficult if you take your time. There are several confusingly different styles of boxes and plugs but they all amount to the same thing.

Going to a series R/R at the same time and doing some 'ground work' on the harness while you're there will make life a lot easier for you and the electrical components in the future. You will never regret it.

The Shindengen SH 775 R/R is a challenge to fit where the stocker went. I installed mine on a plate under the right side cover where the toolkit goes. That leaves the left side with room for whatever you end up running.

[Ktsteuart]

I had a few minutes this afternoon to inspect the wires from the pickup coils and everything seems good there. I have noticed that CDIs for the 450 seem to be a lot more expensive and much less abundant than other models. If I were to ‘upgrade’ to a GS500 CDI, would I need a whole new ignition system, or could I use some/all of the existing parts? I don’t think splicing a new CDI in would be a problem, but I’m not sure I’m ready to gut the whole ignition system.

[Steve]

Please do yourself a favor, delete "CDI" from your vocabulary.

The device you are referring to is the "Ignitor".

A true "Capacitive Discharge Ignition" uses a large capacitor to store up thousands of volts that are created by some flashy circuitry. When triggered by the crank sensor, the capacitor will discharge into the spark plug(s) and start charging again until triggered again for the next cylinder(s).

All GSes still have coils, which are inductive windings (transformers). The only thing that is "stored" is a magnetic charge which is generated by current flowing through the primary side. When the points open, current stops, the magnetic field collapses and a counter-pulse is generated in the wire. That counter-pulse is a change in current, which is amplified by the multiple windings on the secondary side to provide thousands of volts. Your bike does not have points, it has a box of transistors that do the same job. Because transistors can be turned ON and OFF much quicker than points can open or close, you get more time for current to build a magnetic field. You also get better reliability because there are no moving parts. That box of transistors is your "Ignitor". The system in your bike remains an "Inductive Discharge Ignition". It just doesn't have that buzzword "CDI" that was so popular several decades ago on cars.

.

[Ktsteuart]

Please do yourself a favor, delete "CDI" from your vocabulary.

The device you are referring to is the "Ignitor".

A true "Capacitive Discharge Ignition" uses a large capacitor to store up thousands of volts that are created by some flashy circuitry. When triggered by the crank sensor, the capacitor will discharge into the spark plug(s) and start charging again until triggered again for the next cylinder(s).

All GSes still have coils, which are inductive windings (transformers). The only thing that is "stored" is a magnetic charge which is generated by current flowing through the primary side. When the points open, current stops, the magnetic field collapses and a counter-pulse is generated in the wire. That counter-pulse is a change in current, which is amplified by the multiple windings on the secondary side to provide thousands of volts. Your bike does not have points, it has a box of transistors that do the same job. Because transistors can be turned ON and OFF much quicker than points can open or close, you get more time for current to build a magnetic field. You also get better reliability because there are no moving parts. That box of transistors is your "Ignitor". The system in your bike remains an "Inductive Discharge Ignition". It just doesn't have that buzzword "CDI" that was so popular several decades ago on cars.

.

My bad! I had only ever heard them referee to as Igniters, as well as seeing that terminology in the repair manual. In my searching the web for info the term CDI came up and it was easier to type. Also CDI seems to yield more results on eBay. But I do genuinely thank you for the knowledge!

[John Park]

I had a few minutes this afternoon to inspect the wires from the pickup coils and everything seems good there. I have noticed that CDIs for the 450 seem to be a lot more expensive and much less abundant than other models. If I were to ‘upgrade’ to a GS500 CDI, would I need a whole new ignition system, or could I use some/all of the existing parts? I don’t think splicing a new CDI in would be a problem, but I’m not sure I’m ready to gut the whole ignition system.

I think [??] the trigger plate you have will work; you'll need to replace the advance mechanism with the fixed rotor from the GS500. Two screws, one bolt. The hardest part is figuring out the wiring pattern to splice the new connector onto your wiring harness. Not really difficult but you have to pay attention and get it right. Three wires in and three wires out, plus the ground.

I'd try to get the GS500 trigger in the package; if your old one is the same then you have a spare. I've seen the whole lot for under a hundred on Ebay, as I recall.

[Ktsteuart]

Well dudes after a little more fiddling in the garage and a few more hours on the Internet, I found a couple other issues I hadn’t noticed before (one being it looks like the previous owner JB-welded one of the coils together). So I made a phone call to Dynatek. Larry in technical support told me I can use the GS400 kit with very little modification, so I ordered it. I’ll put together an install thread when it shows up. Thanks a million for the support and input guys!

[Steve]

While you are waiting, you are still welcome to come on down to meet a couple other GSers.

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[Ktsteuart]

Let me know when/where! I’d love to get some more exposure to these bikes, and bikes in general.

[cowboyup3371]

Steve, his wife, and one son still living in the house live in Centerville. I'm 10 mins west of him in Miamisburg. There are also quite a few folks just around your part of town

[Ktsteuart]

Do you guys meet up regularly?