Ignition Coil & Spark Issue

[primetimespacetime]

TLDR first for those who don't want the backstory:
- No Spark on the bike.
- Brand New Plugs
- Coils read values within spec at primary and secondary coils (3ohms and 8.6k ohms)
- Coils activate when hooked up to battery (magnetic field will move small metal objects nearby)
- Removed the plug leads as I was having trouble getting continuity with those
- Replaced with plain wire (just for testing) and hooked up multimeter to be sure connection was good
- Still no spark (yes I tried in the dark yes I looked very closely)
Image of test setup below as well as graphic if it's hard to tell what's going on.

Longer version of above:
I picked up an 81 XS400 for free but the thing has been mutilated both physically and electrically by someone trying to cafe it.
I wasn't getting any spark and after trying a few things I ripped the whole loom out.
I wanted to isolate the issue so I've stripped it down to just the coil and the spark plugs.
I was having a bit of an issue with the plug leads so I eliminated them and just ran a plain wire. I made sure that I was getting continuity with those.
I did at one point get a couple sparks but I can't repeat it.
I don't think the coils are shot as they still read within the acceptable OHMs on both coils.
I have a test setup as shown below in the pic. I'm still not getting any Spark.

Thanks in advance!!

 

[CaptChrome]

Welcome to the forum.

Personally, I wouldn't worry too much about this as the coils ohm properly and you have seen the magnetic field from the primary winding and did get a few sparks. It could be that you are inconsistent in opening up and quickly grounding one side of the primary winding to properly collapse the primary magnetic field.

I would move on to getting the wiring sorted and finding the missing stuff that probably got thrown out by the previous owner.

 

[primetimespacetime]

Welcome to the forum.

Personally, I wouldn't worry too much about this as the coils ohm properly and you have seen the magnetic field from the primary winding and did get a few sparks. It could be that you are inconsistent in opening up and quickly grounding one side of the primary winding to properly collapse the primary magnetic field.

I would move on to getting the wiring sorted and finding the missing stuff that probably got thrown out by the previous owner.

Thanks CC,
I would just feel alot better about dumping time into the rest of the wiring if I could find a consistent spark. Or any for that matter

 

[tstidham]

I'm pretty sure the 81 models is an electronic ignition with a pickup coil under the left side cam cover and a TCI timing spark module. The modules are known to have capacitor issues as they age and cause single cylinder spark issues. You can find a few posts on here on repairing those.

 

[jvdavidson]

Well I can't really help you but I can gripe with you... I've been off the scene for a while - my XS400 and I had a severe falling-out in June, 2024. Earlier in that spring, I fired it up for the first time in a couple years (had other issues, sorted everything out, I moved so everything went on the backburner). Back in spring, I had repeat coil failure on the right cyl. Like clockwork, it would fire up cold like an absolute champ and run like a dream for just shy of 1 mile then poof - it's now a 1cyl bike. Let it cool off and the coil comes back online...briefly.

I replaced both coils and she ran like a dream for a couple months until one fateful day in June, 2024. My work had a company outing at a bar/grill - rode the bike up to the bar on interstate and she ran great at highway speeds (about 15mi). Later that afternoon, a severe storm was coming in so I got out in order to get home before it hit since I didn't bring rain gear. Fired up the bike, popped onto the interstate...within a mile I lost my same right cyl coil again and was stuck cursing the damn bike for 14 miles at 30mph on the shoulder of an interstate highway with a severe thunderstorm close on my tail. Made it to an exit, stopped at a Panera Bread to let the storm pass...well when the restaurant closed it was still pouring. Honestly can't remember if the coil quit on the way home that night - was cruising really slow due to heavy rainfall all-the-way home... I was pissed. Parked it and haven't touched it since. Figured the likelihood of buying a faulty coil was low so something else has to be contributing to the coil short out issue at operating temp.

 

[ACHIV]

I'm pretty sure the 81 models is an electronic ignition with a pickup coil under the left side cam cover and a TCI timing spark module. The modules are known to have capacitor issues as they age and cause single cylinder spark issues. You can find a few posts on here on repairing those.

Would you mind elaborating on that further?

I have an intermittent spark in my left cylinder. The right cylinder is strong. I can see it with the timing light strobe. Carbs are good. Seems to be an ignition issue.

 

[tstidham]

If you search TCI issues, you will find several threads on the electronic ignition system. I have a 78, which uses points and a mechanical advance for ignition timing so I don't know much on the electronic system. Pull the small cover on the left side of the head and look. There will either be some mechanical points or a big electronic pickup assembly made of plastic.

 

[jvdavidson]

I installed an electronic ignition system that I learned about on this forum. Think I installed it around 2017 and holy buckets it was amazing. I could set points but the electronic system made starting the bike 1000X easier and significantly better performance.

 

[Durney]

Well I can't really help you but I can gripe with you... I've been off the scene for a while - my XS400 and I had a severe falling-out in June, 2024. Earlier in that spring, I fired it up for the first time in a couple years (had other issues, sorted everything out, I moved so everything went on the backburner). Back in spring, I had repeat coil failure on the right cyl. Like clockwork, it would fire up cold like an absolute champ and run like a dream for just shy of 1 mile then poof - it's now a 1cyl bike. Let it cool off and the coil comes back online...briefly.

I replaced both coils and she ran like a dream for a couple months until one fateful day in June, 2024. My work had a company outing at a bar/grill - rode the bike up to the bar on interstate and she ran great at highway speeds (about 15mi). Later that afternoon, a severe storm was coming in so I got out in order to get home before it hit since I didn't bring rain gear. Fired up the bike, popped onto the interstate...within a mile I lost my same right cyl coil again and was stuck cursing the damn bike for 14 miles at 30mph on the shoulder of an interstate highway with a severe thunderstorm close on my tail. Made it to an exit, stopped at a Panera Bread to let the storm pass...well when the restaurant closed it was still pouring. Honestly can't remember if the coil quit on the way home that night - was cruising really slow due to heavy rainfall all-the-way home... I was pissed. Parked it and haven't touched it since. Figured the likelihood of buying a faulty coil was low so something else has to be contributing to the coil short out issue at operating temp.

Same thing happened to me. Bought a used ingition module on eBay and solved in. I have an '81 xs400 with 70,000 miles on it.