R100S occasional sputter and idle issues. Coil?

[jjwithers]

The problem has re-surfaced, gone away, and resurfaced many times now. I cleaned, blown out, and tuned carbs a few times now thinking it was a carb issue. I checked valves a few times in there too.
After getting my carbs synced perfectly this last round, and still experiencing a fart/hesitation at low RPM load, I went home and replaced the left side coil and spark plug cable with a used coil and cable I had lying around. So far, so good. I had a feeling all along it was something electrical related. I need to take it for a long ride over 30-40 minutes to see if I truly fixed it though. But my 7 mile ride to work and back has been flawless.

[Wobbly]

My ignition would completely cut out at random times while riding down the road. Usually in 250-300 mile increments. Pull to the side of the road, turn the ignition OFF, wait 10 seconds, and then it was OK. I suspected a poor connection in the 12V wiring and had been diligently applying conductive grease to each connection. But it wasn't until new plug wires and new NGK plug caps were installed that it finally went away.

The proximity of the electronic ignition hall sensors and the alternator (and it's powerful magnetic field) may mandate good resistor plug caps.

[Roy Gavin]

A decent coil will jump a 10 mm gap, so if you make up a split
plug lead with a piece of clear plastic tube in the center it isnt hard to check what sort of gap yours will jump
Get someone else to hold the lead while you start the bike--------.
Plug caps dont last forever either, and usually start breaking down at high revs.

[jjwithers]

My problem is back but much worse. The left side is not firing at all now.
I had the issue at work, and in high RPM, both sides will fire, low RPM, the left side will not fire.
I'm wondering if it is the box for the dyna ignition finally dying on me after 40k miles on it?
Or??? any other ideas?
It is a R100S, mostly stock with the dyna electronic ignition.

[Kurt in S.A.]

The Dyna plate that replaced the original points plate needs a good ground against the engine. Pull the plate and clean things up to see if it helps. Probably will mean that you'll need to reset the timing since the donut that's clamped to the advance until will need to come off.

Kurt in S.A.

[Wobbly]

The only coils I've replaced as a pro bike mechanic are the ones where the owner disconnected the plug leads while the bike was running. Occasionally you'll see someone on the internet proposing this as a way to balance dual carbs or test something. Don't do it. Once created, that 25kV must get to ground... even if it has to burn it's way out.

If you must test the plug firing, first remove both plugs. Insert them into the plug caps and lay the metal portion of the plug on the cly head. Use the kick start if it has one, otherwise only use the electric starter for no more than a couple of seconds.

[jjwithers]

one cylinder was firing on the bike.
I moved the spark plug cable to the non firing side, and everything worked.
I tried different plug cables, and that wasn't it.
I replaced the coils and Bingo! both sides fired. I ran the bike about 2 miles and put it away.
The next day, same issue. Left side stopped firing. I put in a new spark plug and Bingo! I put about 45 miles with (about 4 stops) on the bike and not one sputter, not one issue.
So... i am still left scratching my head as to why replacing a coil would make the bike run OK, but the problem seems to have been a faulty plug all along... that would intermittently work.

[Zombie Master]

Weak battery.

[jjwithers]

Weak battery.

It's a brand new Odyssey!
And this happened with the previous battery, which was fine, i ended up switching it to another bike for design/space reasons (it was an alien motion battery).

However, while riding, my cockpit volt meter sometimes is at 12v no matter what lights I have on, and other times is around 13v. I've gone over it with a volt meter and it was always a 12.8+ so I just figured it was an inconsistent volt gauge. I have a modern electronic voltage regulator.

[Kurt in S.A.]

Sounds like the bad plug had some kind of spark energy threshold in order to fire. The new coil was able to more consistently meet or exceed that threshold for a little while. But if the coil sends energy down to the plug and it doesn't fire, where's that energy going to go? Likely it will bounce around within the ignition system, potentially created havoc over a period of time. So, new plug and new coil, all things are good and the energy is able to jump the gap and find it's happy place...ground!

Kurt in S.A.