Forgot to mention... solenoids wear out too. The coil may fail or stick or the contacts may burn to the point of not conducting. Think of the sparks you get if you touch battery cables together - the contacts in the solenoid deal with that every time you crank the engine.

My aftermarket starter button sure felt dead. No click from the solenoid. Nothing. I replaced the button, so if that had anything to do with anything, I should be good.

An ignition switch does not power the starter directly. It energizes a coil in the solenoid which closes a much stronger switch capable of carrying the heavy current needed to turn the starter motor. If the battery is low, it may show 12v but not be able to supply the amps needed for the starter. When you turn the ignition switch or press your starter button, it may have enough juice to trigger the solenoid but not turn the starter. When this happens, you may hear the solenoid click or rattle but the starter won't move. The voltmeter reading would also drop significantly.

Note on very early Minis with a floor starter button on the tunnel, this button acts as a manually operated solenoid. On these cars there would not be a solenoid or a 'start' position on the ignition switch.

I've replaced the starter button and disconnected most all electronic gizmos that may be putting a load on the battery/alt in an attempt to troubleshoot the electrical system. As I mentioned, the misfiring occurred durning what was probably a low battery condition, although I neglected to check the in-dash voltage meter during the misfiring. A low battery doesn't explain why the starter switch would go dead during each misfiring episode unless there wasn't even enough current to power up the starter button relay. Is that even possible?

I've ordered a new high-output 55w alternator and will be keeping an eye on the battery. The battery is 5 yr. old Optima Red Top and I usually get 8+ years out of a Red Top on my daily drivers, but we all know our Minis are special.

Start as Spank suggested early on, by disconnecting the trickle charger from the battery and car electrics. Even if not defective, when not plugged in to house current, it could possibly be a phantom load - the battery trying to "charge" the charger.

Yeah, I thought 12.9 was a little low too. Alternator is new, although I believe it's only a 30A model. Didn't think I needed anything bigger as I have only minimal electric accessories—no radio, heater, fog lamps, etc. Here's another clue that may point to the battery; both times the missing/stalling issue occurred the battery was in a low charge condition. The first time was after driving 40 miles to the track followed by an hour of hard driving. I always plug in my smart trickle charger overnight, except the other day. That was the day the missing/stalling occurred for the 2nd time.

Still, the momentary dead starter button leads me to believe the ignition toggle switch is the likely culprit. So, this is the order in which I'm going to pursue this: ignition switch --> battery --> alternator --> coil. Will advise.

That would explain why Rosebud starts so easily. I've always been amazed; a quarter turn of the crank and bam! She's running.

I wouldn't have thought there was a lot of current running through the ignition switch, but all clues point to a bad switch. I'm swapping out the old 20A switch for a 30A today. Will advise. Thanks.

I'd be expecting to see more than 12.9V with the engine running.

Is the battery just going flat due to a pathetic alternator ?

Ian may be onto something with the kill switch if you are using it to start/stop the engine every time. Its internal contacts may not be up to the arcing that occurs (even at 12v).
The shaft of a 123 would not have any rotational slack in itself. All it does is drive the rotor and provide static timing (at zero advance) to the electronics. Once the electronics read 500 rpm the selected (or programmed on some later versions) advance curve is applied, starting at the preset idle speed advance. If equipped with vacuum advance, that is also applied. One nice thing is that with zero advance during start-up, starting the engine also becomes very easy. A warm engine (mine anyway) will start at the touch of the key - enough to bring the next cylinder into firing position.

Hi Michael,  a bit of wiggle rotation wise is normal for a clockwork distributor ... don't know if the same holds for the 123....

I would be suspicious of the battery charge.  I would consider your readings to be a bit on the low side.  With points this may not matter but my experience with an electronic ignition system (Piranha) was that the amplifier did not like low voltage...  High revs also reduce the dwell time (period the coil is charging); the coil output will be further compromised by a low input voltage.

However, your initial comments re the intermittent lack of an ignition light points to some sort of loose wiring or flaky (earth) connection....maybe with the ignition switch???  If the light is not on when the engine isn't running then the alternator will not charge (even if you get the engine running... which you won't  as this voltage also drives the ignition system - or at least it should - if things are wired up correctly). In the normal scheme of things, the voltage that lights the light also creates the magnetic field necessary for the alternator to provide an output....and energises the coil. 

IMHO the low battery charge is an outcome not a cause of you problem.....

Kill switches are double edged sword.  They (should) isolate the battery - but should only do so when told to.. A few years ago at MME meb and I solved a Rover drivers erratic running (symptoms similar to those you describe) by giving his kill switch/battery isolator a good whack with a shoe....

Cheers, Ian

The rotor fits tight on the distributor shaft, but the shaft itself has a 2 - 3 degree wiggle. Gear lash? Still in spec.?

Spank already said

A fully charged battery should be able to do several autocross runs without an alternator.

It takes a bunch of current to run the stater motor to start the car.
After started, the drain on the battery by ignition itself is small.

take the battery to a parts store and have them load test it. Then you'll know if it should be replaced.  Do it twice. Once now, and then take it home and charge it up. See if it passes. If it does pass, go do your heavy foot racing and see if it has the same symptoms.

Then proceed to #2.

higher rpm places more demand on the ignition system, yes, so thereby the electrical system. A faulty coil or bad wires or even a bad ground can be taxed more under higher rpm conditions and reveal ' exploit their weakness.

Check to see how tightly your rotor fits on the 123. I've had them fit loosely and wiggle previously causing interesting running conditions. The grove/tang setup that only allows the rotor to fit on one-way seems to wear on these more than it does on lucas distributers. And the little metal spring on the rotor also doesn't seem to keep its "boing". Not sure if that is really a grave issue, but a wobbly rotor can disrupt the spark. By and large, though, the 123 distributers have been flawless for me. Love 'em.

1. Battery cables good.

2. Hadn't considered the "toss factor." Eliminate trickle charger for a clean test—good idea.

3. Great idea. After all, the tach is already suspect.

4. I'm hoping the ignition (kill) switch is the culprit. 

5. Another good thought—although I paid for a bladder, so their better not be any foam bricks in there.

6. Stuck choke, separate issue. [link]

7, 8 & 9. All good.

10. I'll do a good, clean check on the battery.

So, does high RPM driving put a greater load on the battery, alternator, coil? I'm thinking more pulses per sec. = more current needed?

I have driven older cars with points and on more than one occasion with no battery or a bad battery, as long as the car has minimal electronics it will run with little to no battery as long as you don't use lights, wiper, heater blower, a/c etc.
So No i don't think the battery is an issue unless it has an internal short which from my experience will be permanent no coming and going at different times.
While you think the connections are good you need to check the main positive cable underneath the car.

Do the simple things. Don't assume it is the ignition switch.

Check your battery wire as others have said.

the autocrossing tosses your car left and right. unsecured wires, like those in your trunk, can wiggle around. the trickle charger it looks like you've got I would remove to eliminate that as a possibility. Also if your tach isn't disconnected go ahead and make sure it is isolated away from the rest of the system.

I've had kill switches go bad and mimic what you are describing. Not sure if you have one but question that.

Is there foam in your fuel cell?

Why were you fiddling with your carburetion?

Check your plug wires for secure connection.

Check your plugs.

While plugs are out, do a compression test.

A fully charged battery should be able to do several autocross runs without an alternator. Make sure you battery is charged fully, just unplug your alternator, and go drive and see if the sputtering continues. Your dash light will be on, but you at least won't be getting any spikes or reversed charge spikes--- you may have a bad diode in your alternator and the 123 will be super sensitive to that, I suspect. But unplugging your alternator will remove that as a variable.

Pretty sure I've got a good battery ground—it's pretty tidy in there. Let me ask you this: If my battery is on the low side and my alternator is not keeping up, would WOT driving reveal the battery's shortcomings? In other words, does high RPM driving increase the demand on the battery and/or alternator? 

You've raised some interesting issues. I was hoping for a simple switch swap. 

1. The tach is electronic. Unfortunately, no one has been able to make it work correctly. I installed it myself and when it didn't work had two auto electric shops scratch their heads and tell me my new Smith's tach is broken. Ref: forum link. 

2. 45 minutes of redline WOT track driving. Thought if the coil was going bad I might have overcooked it.

3. Good point. I always thought the battery was a little on the low side. I'll look into it.

4. I'm not necessarily sure it's the correct coil. It was installed by the same reputable Mini shop that built my engine and installed the dizzy. I assumed they were correctly paired. I'll check the ballast/non-ballast issue and make sure I have the jumper wire in place.

Other than the apparent connection between my ignition problem and hard driving, it sounds like a simple ignition switch issue, right? If it were the coil acting up, why would my IGN light remain dark and the starter button be dead with the ignition switch turned on immediately following a missing/stalling episode? Maybe the hard driving thing was just a coincidence. And 2k miles of trouble free driving with the same coil, battery and dizzy before it began acting up again. I'm hoping it's just a short in the ignition switch. Will advise.

As the red ignition/charging light is coming off an on check your main battery cable underneath the car sometimes they have been known to short out on the exhaust also make sure the connections are tight on the battery cable ends and your engine to chassis ground is tight and clean also.