Intermittent Dead Cylinder...Switching Sides

OK I Put it here again where I am at others can come in
There has been done extensive work on carburetors
And Electric Service at some parts
The sparking at the points appears good. on both sides please check again
The sparking at point when one Cylinder don't fire

Now I believe what happens is that the shifting of sides has nothing to do with Carbs
its a weak spark and the blipping of one carb revs up the engine and affects the intake parameters on the other carburetor
that has closed butterfly valve --affecting mixture and the weak spark cant light it up exactly as when the Alternator rotor is fried
Soft on the throttle it runs but not if you try to open up
( That single side blipping is not possible on newer bikes )
i believe ( I do understand I Sound like a parrot ) that we are talking a weak spark
either because of weak charging which the fluke measurements will show or a cable or so partially shorted out
Which can be very difficult to find a especially with no proper place to work at.
But lets solve that later if need to do so.
The capacitors as mr Team Junk has it 50 year old capacitors are especially sketchy.
I would replace It is not that expensive
It is a well known fact that capacitors age and go out of spec in fex old HiFi
I However don't believe it is the fault here
But by looking at the bikes status and long time ownership I feel that replacement would be good
If workspace can be found
An experienced mechanic would also inspect the alternator brushes before or after the Charging Voltage measurement across the battery
The outer one at least ( Higher mileage )
Parrot again
The fuel is there
The spark is there
BUT the spark is to weak .. The single side blipping extinguish the fire / combustion / Ignition at the other side because to little air in the Mixture

Lets see what happens I have been wrong before but in this case Jaeehhh lets see
 
One thing to try is closing the gap on the plugs. Helps with weak hi voltage.
Or check if both plugs and caps are resistor type. Resistor caps OR resistor caps is ok, both are not.
But still, if the hi voltage is too weak to fire plugs at the correct gap, something is off.
- Poor battery voltage, which seems to have been ruled out.
- Voltage at coil + is too low (again, poor connections in harness, ignition switch, kill switch. On my 77 this was bad enough to not make any spark at all. Fixed it by doing the "relay mod", that the OP rejected)
- Too much resistance between coil - and ground (bad connectors, bad or dirty points)
- Insufficient dwell time to reach saturation in coils ( worn points cam, slop in advance shaft, low quality points)
- Bad capacitor/ condenser
- Bad coils
Bad grounding of points plate, capacitor/condenser, or the engine itself.
 
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One thing to try is closing the gap on the plugs. Helps with weak hi voltage.

Just tried that. No change.
Oh, and plugs were just changed (B8ES). I've had three different brands of plugs with all manner of experimental gapping (beginning with specified gap!) since this all began. Made NO difference.
 
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Or check if both plugs and caps are resistor type. Resistor caps OR resistor caps is ok, both are not.
But still, if the hi voltage is too weak to fire plugs at the correct gap, something is off.
- Poor battery voltage, which seems to have been ruled out.
- Voltage at coil + is too low (again, poor connections in harness, ignition switch, kill switch. On my 77 this was bad enough to not make any spark at all. Fixed it by doing the "relay mod", that the OP rejected)
- Too much resistance between coil - and ground (bad connectors, bad or dirty points)
- Insufficient dwell time to reach saturation in coils ( worn points cam, slop in advance shaft, low quality points)
- Bad capacitor/ condenser
- Bad coils
Bad grounding of points plate, capacitor/condenser, or the engine itself.

UPDATE:
Voltage at battery terminals with ignition OFF: 13.4V.
Voltage at battery terminals with ignition ON: 13.2V.
Voltage at battery terminals with engine idling at ~2,500rpm: 14.1V~14.4V (it increased as the engine warmed, although the rpm's remained the same).
Voltage at battery terminals with engine idling at ~1,100rpm: 13.6V.

Unfortunately, today, we're back to the right cylinder backfiring at ~1,100rpm idle (but OKAY with choke ON and idling at ~2,500rpm). Pulling the spark plug lead on the right cylinder has NO effect on idle. Pulling left spark plug lead stalls the engine. Less than two minutes later, the problem shifts to the other side, but without the backfiring.

Once again, I pulled the points cover and, as best as I could tell (overcast daylight sky) both points were sparking. But it's difficult, at best, to tell how strong the sparking is whilst observing things in the middle of a busy public parking lot (again, the bike's stored in a public storage unit and tests/repairs are prohibited on the premises, so I have to work quick and "under cover").

Anyway, at that point—cold and VERY frustrated (this's been going on for nearly two years)—I packed it in for the day. I apologize for being unable to perform some of the other requested tests, but I'm now repeating alot of the same tests/checks for the third and fourth time. Ugh (frustrated).
 
You still haven't checked voltage where it actually matters, at coil + terminals, under load. That is with the associated points closed. Ignition on, but engine not running. The coil is basically a resistive load, drawing 3 A or so. If voltage is below 12 V, something is amiss between battery + and coil +.

Neither have you checked voltage drop between coil negative and ground, with the associated points closed. Basically hook voltmeter + lead to coil negative, and voltmeter - lead to battery negative. Ignition on, but engine not running. The voltage should be very low, ideally zero. A voltage reading above 1 V or so, indicates poor connections/ conductivity between coil negative and battery negative. This includes bullet connectors, wires, points, and grounds.
 
Carburetors have been serviced
Charging is there.
So it is the ignition circuit that needs attention and service as mentioned and arcticXS in #87

Capacitor replacement fex
https://www.ebay.com/itm/362968236543?hash=item548297c1ff:g:akoAAOSwIKdhUvOj

Kill switch and downstream
I would install a voltmeter to ensure that nothing is shorting or overcharging
I understand it can be difficult without a place to do it
But the info here can be given to the one that will do it saving time.
 

That's been suggested many times over the years, but I am keeping the bike OEM. It worked fine as designed and it'll work again once the defective part(s) are identified and repaired/replaced.


Kill switch and downstream
I would install a voltmeter to ensure that nothing is shorting or overcharging

If there was an easy way to check this whilst in a public parking lot (which prohibits vehicle repairs) and I had seen your request BEFORE making the trip over to the bike this morning, I would've added this to today's work. Unfortunately, at this point, after going around in circles, trying everything recommended without result for nearly two years, I think I need a better plan.


I understand it can be difficult without a place to do it
But the info here can be given to the one that will do it saving time.

If there was someone local who was able to repair the bike, I would not still be posting. Unfortunately, none of the local bike shops are willing to touch the bike due to its condition (near mint) and age.
 
You still haven't checked voltage where it actually matters, at coil + terminals, under load. That is with the associated points closed. Ignition on, but engine not running. The coil is basically a resistive load, drawing 3 A or so. If voltage is below 12 V, something is amiss between battery + and coil +.

Neither have you checked voltage drop between coil negative and ground, with the associated points closed. Basically hook voltmeter + lead to coil negative, and voltmeter - lead to battery negative. Ignition on, but engine not running. The voltage should be very low, ideally zero. A voltage reading above 1 V or so, indicates poor connections/ conductivity between coil negative and battery negative. This includes bullet connectors, wires, points, and grounds.

As I said, after two years of this, I've likely missed a few posts, so I apologize if you've recommended this previously. But I honestly don't recall seeing it. Did I mention that I'm feeling a bit overwhelmed at this point?
And, again, I wish I'd seen this BEFORE making the trip to the bike this morning, but I'll give it a try next time. Thank you.
 
A capacitor is something that is ageing over time going out of spec or worse
It is pretty much the first thing that's gets renewed getting an old hifi up to performance again
please Google

fex
How long will electrolytic capacitors last?
Manufacturers of electrolytic capacitors specify the design lifetime at the maximum rated ambient temperature, usually 105°C. This design lifetime can vary from as little as 1,000 hours to 10,000 hours or more.

A weak condenser will cause a weak spark, because the voltages will rise higher, but little energy will cycle through the spark plug. If you look at the plug with a weak or open condenser, you'll see a thin, purplish arc, as compared to a strong, blue-white spark.

That's been suggested many times over the years, but I am keeping the bike OEM. It worked fine as designed and it'll work again once the defective part(s) are identified and repaired/replaced.

It is like Tires and Oil one does not use these all over the bikes life span .. If it does not change the problem -- capacitor change
You can always put it back ( the old One ) If it is a must
A electronic shop can test them I do Believe
Neither can one have a wiring or switches all over the bikes life span in all cases
This is things I have tried over the years ..trying to repair things instead of replacing
And trying to save money ..But instead have to put in many hours of work Becoming an expert on wiring lol
A possibility you don't have as it seems
And the likelihood for problems increase with age and wear.

Sometimes you can keep the parts but not always
I believe a shop should they take on the job would
Replace coils capacitor and points as a first ---call it Preemptive strike.
It can be time consuming and expensive in shop hours . Not having updated to a benchmark .
If one cant find the problem which can happen with problems not always there Rain fex Then one way forward is replacing
 
Ok if you want a plan to figure out the problem you will need 2 voltmeters you can attach to the bike while you ride it.
Each coil needs to have a volt meter attached to the battery side of it. When the bike acts up you will be able to tell if it is a wiring problem to the coils. If they are both 12+ volts the problem is not in the switches or wiring. If one coil is a lot lower on voltage then you know the trouble is upstream of the coils. All you have to do is move the meters upstream until you isolate the problem.
If you have not changed the condenser pack I myself would do that first.
If the volt meters read over 12 then it will take 2 dwell meters to prove or disprove the rest of the ignition system.
 
I think @Jan_P maybe on to something here. Capacitors (condesors) have a finite shelf life because the electrolyte dries out. The location of the condensers in the heat of the engine speeds the process. They are a wear part.

In addition the ground for the condensers is one of only common connections in the dual ignition system.
 
I believe a shop should they take on the job would
Replace coils capacitor and points as a first ---call it Preemptive strike.
It can be time consuming and expensive in shop hours . Not having updated to a benchmark .
If one cant find the problem which can happen with problems not always there Rain fex Then one way forward is replacing

Sorry, I misunderstood you. The condenser (capacitor), points and regulator were changed last year, per another contributor's recommendation. No change. The coils were changed a couple of months ago. No change.
 
In addition the ground for the condensers is one of only common connections in the dual ignition system.

Thanks. All of the grounds and connectors running between the ignition- and kill-switches and the coils were disassembled (i.e., unscrewed or pulled-apart), cleaned—mechanically and chemically—and treated with contact cleaner before reassembly. No change. Details in one of the previous posts within this thread.
 
It's obvious you do not have a easy or normal problem. You are going to have to diagnose by ruling out things.
 
Without going back and reading the whole thread (yes I’m lazy), I just wanted to comment that I had similar issues of a dead cylinder that moved from side to side. I am running a Pamco and hunted down electrical gremlins but found none. Turned out to be the tune of my PWK carbs. Got that sorted out and the bike ran well. Since that time I have gone back to BS38’s and the bike runs very well now.
 
This is difficult
A listing of what has been performed and replaced would help
Points ? Coils ? Plugs and so on Intake Boots etc etc
Given what I hear that the carburetor is serviced
That the charging is there

I feel it to be the ignition
I believe mr ArticXS are at the right things post # 87
And GLJ in # 92
Installing one Voltmeter temporarily at the Point where the lead to coils split is not that difficult
at least not on my 80
A uploaded video would help perhaps getting a feel how it runs and starts
 
Ok if you want a plan to figure out the problem you will need 2 voltmeters you can attach to the bike while you ride it.
Each coil needs to have a volt meter attached to the battery side of it. When the bike acts up you will be able to tell if it is a wiring problem to the coils. If they are both 12+ volts the problem is not in the switches or wiring. If one coil is a lot lower on voltage then you know the trouble is upstream of the coils. All you have to do is move the meters upstream until you isolate the problem.
If you have not changed the condenser pack I myself would do that first.
If the volt meters read over 12 then it will take 2 dwell meters to prove or disprove the rest of the ignition system.

Not sure if this was meant in fun, but it's not gonna happen. Beside the fact that the bike's generally not rideable, even when it is, if I'm carrying two VOMs, where's my drinks cabinet supposed to go?

Seriously, I appreciate the input and two VOMs might help in a garage, but not on a currently unreliable bike.
 
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