1982 Seca no spark after rainstorm

Hi guys,
I'm a little lost on this problem and I'm hoping someone here can point me in the right direction. I've got a 1982 XS400 Seca that was running as of early August but now has no spark on either side after it was out in a good rainstorm. I have the service manual and I've been attempting to find the problem for the past few weeks but everything seems to be in good shape. Here's what I know:
Battery: I think is good, holds about 12.1V when bike is off, drops to ~10.5V while starter is engaged
Fuses: all good, I've tested for continuity all the way from the positive terminal of the battery to the R/W wire into the TCI and both ignition coils
TCI: I'm not sure what I can test on it, but I know it's recieving power, all connections are good, and there is no corrosion/obvious damage inside.
Ignition coils: I can not access my coils because I can't remove the bolts connecting the top of the engine to the frame. I can reach the plug for the left coil and I know the primary coil resistance is within spec. Both the orange and grey wires show ~10V with the key on, so there aren't any breaks or disconnects in the wire.
Spark plug cables: seem to be in good shape, it doesn't sound like they can be removed
Spark plugs: brand new non-resistor plugs. I got new plugs about two months ago, but already replaced them b/c they were covered in soot.

I have two theories:
One, that rain got in both of the ignition coils or TCI somehow and rendered them non-functional; or
Two, that my engine has been running very rich and fouled up the plugs, and my repeated attempts to start the engine while a spark couldn't get across the gap somehow burnt out the ignition coils or the TCI.

I'm at a bit of a loss here but if someone has dealt with a similar situation or knows something else to try, that would be great. Can fouled spark plugs burn out ignition coils? How hardy are the coils? How would I test if the TCI is commanding the coils to fire?

Thanks
Alex

Can fouled spark plugs burn out ignition coils?

No, it's even easier to jump spark, it goes down the side of the porcelain instead of through the gap. The soot is carbon which is a conductor. Wet but clean plug will do the same.

If somebody you know has an older analog needle type voltmeter you can check the magnetic pickups on the ignition plate, they are what commands spark to happen.

Odds are the battery is bad and at least contributing to the issue, that volt number says dead battery, you must have a minimum of 12.3 up to 12.8 volt to be a good battery. Vehicles commonly show battery issues at under 12.3 volts. The starter then saps the extra power the ignition needed to work, no start.

Thanks for the reply!

And I was so worried about the spark plugs...
I don't know anybody with an analog voltmeter, but could I put the bike on the center stand, put it in 1st, and turn the rear wheel to test the pickups? And with that same setup, would the spark plugs fire without the starter engaged? That would at least let me know if the coils can spark when the battery is ~12V.
I'll take the battery back to BatteriesPlus tomorrow, see what they say about it. Maybe have them try discharging it and see if it holds the voltage it should. How low should the voltage drop when the starter is engaged?

I don't worry about the last until the overall battery volt issue is solved, the volts starter pulls down to is greatly affected by the condition of the starter and all connections to it.

The battery should charge to be full then sit 8 hrs. and still be above 12.2 volts. The shop should be able to load test it by advertised CCA to tell whether it is good as well.

You still need to worry about plugs, when they short down the sides the best they can produce in spark is a misfire. Makes engine hard to start.

'...could I put the bike on the center stand, put it in 1st, and turn the rear wheel to test the pickups?'

No but maybe it's best you try so you'll know why. Too much load, you can't turn it enough. Best would be plugs both out and bike in neutral and kickstart engine, they will read even key off. Or use starter and kill switch to engine off. The pickups make their own power

I'll get the battery tested and I just bought a battery charger as well, so I don't have to keep going to BatteriesPlus.
And I just bought brand new plugs, that's why I'm not worried about them.
Thanks!

Coil test...............kill switch to run and spark plug out but connected to plug wire and plug MUST be grounded on the bottom end touching head. Take the orange wire off each coil to hold it by hand and then ground it to metal on bike for 1 solid second with key on and then take wire off, the plug will fire every time when you remove the orange ground. It will be hard to see if the plug is fouled, new is better to force the spark through the airgap.

You are bypassing the ignition box and pickups doing that.

I'll see if I can do that tomorrow, but one of my problems is that I can't reach the ignition coils on my bike. They're tucked up in the frame and I don't have the necessary tools to remove the engine to reach them. I'll try that if I can though!

Not familiar with the exact bike but you generally remove fuel tank to get at most coils, removing the engine just isn't done.

(Edit) yes, the '82 service manual clearly says to remove the fuel tank and then disconnect the coil wiring to completely remove them next. If seat folds up maybe it clears but on some bikes the seat has to remove to remove tank, not that hard though. On my huge Honda DOHC it only takes 3 bolts coming out to do all that.

I had to use a breaker bar to remove some panels, but I got the coils out. Unlike what it shows in the service manual, I have two separate ignition coils. I tested them as you said and neither one produced a spark. Both primary coils show a resistance of ~2.7ohm, within spec. One coil shows a resistance of ~56kohm between either the 12V or ground wire and the output, while the other has ~8.8kohm across the same points. From my basic knowledge of ignition coils, I don't think there should be any continuity between those points, so something is damaged internally. I'll look into replacing them now.

Ooh, and the spark plug wires are not great. One doesn't have continuity, the other shows 0.5Mohms on my multimeter. Do you have any experience with replacing spark plugs wires and/or caps?

It's the caps. I removed them from the spark plug wires and one doesn't show continuity and the other shows the 0.5Mohms. I'll get right to replacing those

I'm at a complete loss at the moment. I got some used coils off of ebay from a salvage XS400 that test correctly for primary and secondary coil resistance. I got new spark plug caps with 5kOhm resistance (I have non-resistor plugs). I trimmed the plug wire to make sure the connections were good. But the bike still has no spark. So I tested the coils like amc said on September 7th, no spark. I connected the coil directly to the battery, no spark. Did I just happen to get another pair of bad coils or is something else wrong here?

You should have around 4 coils now and the odds of all being bad are likely in the millions. Quite likely you are not testing them correctly.

That's what I'm leaning towards, but I'm not sure what I could be doing wrong. I'm planning on moving past that for now and assuming the coils work, but that the bike isn't providing enough voltage to the coils. With a fully charged battery, I was only measuring ~10V on the positive side of the coils, so there's some unexpected resistances in the wiring harness I need to track down next. The PO did some modifications to the wiring as well, I'll have to replace/fix a couple connections.

Look at the kill switch, often the resistance is there.

And look at the battery too, if not over 12.3 volts you got issue there too.

When trying to start the bike, I measure about 9V going into the coils. This seems like it has two causes:
When the starter is engaged, the battery voltage drops to around 10.5V (from 12.8V). Does your bike drop that low amc or is my battery bad?
Without the starter, but with the key on, the coil voltage is around 10.5V, due to what seems like several small voltage drops across parts of the wiring harness, ignition switch, main fuse, and kill switch. They're all small (<0.3V each) but they all add up so that the battery voltage never makes it to the coils.
The combo of the two means that the coils aren't getting enough voltage, which is the reason for the lack of spark (I think).
For anyone reading, could you measure your battery voltage when you're starting?
It's worth mentioning that I measure 0.1Ohms (the minimum my multimeter can show) between the positive battery terminal and the coils. There's just a lot of amps flowing through the whole system.

If bike is running right it should kickstart, no starter draw then.

If battery is showing 12.8 volt right after charging let it sit overnight and then give a number. Is battery new? 9 volts at coil is not enough.

My bike doesn't have a kick start ('82 400R) unfortunately. I've had it sitting on the charger for a whole day, I'll unplug it before I go to bed and update in the morning. It's usually been around 12.8V, it just drops so much when running the starter motor.
Do you have an XS400 or are you just a motorcycle guy? I'd like to compare batteries if possible, see if mine is underperforming. I got it new in July:
https://www.batteriesplus.com/produ...rcycle/yamaha/xs400/400cc/1982/cyl12n12a4a1xt

I do not have one. Regardless, all batteries are comparable. Bike should not be that low volt at the coils. You seem to be saying that the battery has 12.8 volt at stabilized, or after sitting overnight (at least 8 hours to dissipate all surface charge).

Yes, after sitting for 18 hours off the charger, it's stable at exactly 12.8V. I put it on the bike and turn on the key, the battery drops to ~12V and the coils show 10.5V. With the starter on, the coils bounce around 9V.
What's the minimum voltage it takes to get a spark out of the coils?