Major Stumble, Misfire. Troubleshooting Help

[Janky59]

Hello guys, my 1992 907ie recently (a week ago) developed a significant engine stumble. I’ve owned it 2.5 years, it is usually a reliable starter and steady runner.
I’ve read many posts here for troubleshooting, have done some tinkering but I’m getting nowhere.
It started normally last week on the high idle lever, normal crank over and no throttle necessary. While I was putting on my gloves it dropped in rpm a lot, then stalled. I restarted it, but it needed some throttle and didn’t sound like usual. I continued out on my ride, but knew right away something was off. I was hoping riding it and getting it hot would sort it, but no luck. The temps were 60’s-70’s, quite routine. After a few miles the engine temp gauge was reading normal.
I ran thru the gears hard, no change. I did that again with steady throttle for a bit at 6K-7K rpm, no change.
So what is going on is: the engine is stumbling badly, I think 1 cylinder is dropping in and out randomly. It will run/pull normally for 2-3-4-5 seconds, then there will be a split to maybe full second of reduced power. It’s not totally dieing, it stops pulling hard and sounds different, then it picks back up for 5-6-10 seconds then stumbles again.
Starting it since this glitch, it needs the throttle opened for it to light off.

I have an audio clip saved, but it doesn’t look like the site will let me upload it. And the video clip is too big to upload.

Particulars on the bike: 907ie, mostly stock. 20,650 miles. Belts and valve clearances set before I bought it at 16K or so miles. It does have a pair of Termi slip ons, big hole in the top of the airbox with an K&N filter, and a Feracci ECU chip. Earth X battery.

IMG_0809.jpeg (362.35 KiB) Viewed 484 times

So far I’ve:
Unplugged/reseated any FI related connections I can get to.
Looked over the grounds.
Unplugged/reseated the side stand switch.
Unplugged/reseated the ECU connector.
Unplugged/reseated the 3 coolant temp connectors on the coolant manifold.
Installed fresh spark plugs.
Removed the air temp sensor and verified it responds to warm and cool airflow.
Measured both coil primary and secondary resistance values, 0.5-0.6 ohm and 4.5 to 4.7 k ohm.

All help appreciated…

[higgy]

The first thing I would do is replace the in tank fuel filter. After which I would make sure the fuel pump is working.
After verifying the filter and pump time to do some voltage drop tests
start with the fuel pump relay. both sides
and then the coils

see where that leaves you

[Janky59]

Here’s a link to a YouTube video that my daughter helped put together. Part video clip and part audio clip.
Take a look and a listen.

https://youtu.be/LJqv_ei3y_U?si=jOJShZr_Z0oG7oPO

[higgy]

I have moved my filter for easier access as well. Still I would start there. Running on one cylinder for sure. Did you check for water in the fuel?
easiest way to check for that is to drain the tank. Other possible issues could be the spark plug wires leaking somewhere along their way to the plugs.
all I can think of at the moment. Lets us know what you find

[Janky59]

Higgy, I didn't check for water. But with it apart some, draining the tank will be easy to do.
I've thought about the plug wires for sure, and coils.
Something I did yesterday was to start the bike, ran it for maybe 5-6 seconds with the idea to touch the horizontal and vertical exhaust pipes right out of the head and see if there was a notable temperature difference.
Both got hot to the touch, but the vertical seemed a little cooler.
I based this on how long I could keep my fingertips in contact before I had to pull away.
The horizontal had more "ouch" to it than the vertical. A little subjective, but I think it's an indicator.
Maybe I'll buy one of those infrared temperature guns or call some friends.
Anyway. this will all have to wait a bit as Mrs. Janky59 and I are headed on a road trip to Fl this morning.
Updates to come, regards.

[Janky59]

Update: I sourced a new coil from Gotham Cycles, installed it for the vertical cylinder, no improvement. Then I ordered a set of plug leads from Magnecor, initially 1 wire was too short, so I got that sorted with them.
The replacement wire from Magnecor arrived yesterday, things reconnected etc. and no improvement.
I did get ahold of a non contact thermometer. The vertical cylinder is the issue. Its exhaust pipe temperature close to the head was 80-90 deg F lower than the horizontal one. I going to injector cleaning next.

[higgy]

What are the specs on the new coil ?