Intermittent Dead Cylinder...Switching Sides

Check all your ground wires it is the only thing common to both sides of the 2 ignition circuits

Again, I'm not sure how static ground wires would result in a dead cylinder intermittently shifting from right-to-left, then, intermittently, from left-to-right, then, intermittently, not affecting either cylinder, then, intermittently, shifting back to the left....? But I'll certainly check them.
Thanks.
 
Bad camshaft bearings or worn advance shaft bushings, allowing the points cam to move around, is at least a theoretical possibility.
I once came across that kind of problem on an RD350 with bad main bearings. New bearings fixed unstable ignition timing and cylinders cutting out.
 
Bad camshaft bearings or worn advance shaft bushings, allowing the points cam to move around, is at least a theoretical possibility.
I once came across that kind of problem on an RD350 with bad main bearings. New bearings fixed unstable ignition timing and cylinders cutting out.

Not to be argumentative, but if the bearings were so bad that they were causing alternating cylinders to cut-out....and, sometimes, normal operation....wouldn't there be other issues? Bearing noise, overheating, etc.?
 
Not to be argumentative, but if the bearings were so bad that they were causing alternating cylinders to cut-out....and, sometimes, normal operation....wouldn't there be other issues? Bearing noise, overheating, etc.?
On that RD, it wasn't obvious until I checked the timing with a strobe lamp.
Of course, that points cam was on the end of the crankshaft, so not exactly comparable to an XS setup. But still something to check out. At least worn advance shaft bushings would not be audible or otherwise that obvious.
Anyway, removing the points cover, and checking the points cam for any movement or play is pretty quick and easy.
 
What about poor connections at harness connectors, in the ignition lock (main switch), kill switch, etc?
Lots of possibility for excessive resistance and voltage drop. Try testing with a direct wire from battery+ to coils+, and see if that fixes it.
As I have mentioned numerous times, the original current path (wiring, connectors and switches) from battery + through coils and points to ground is extremely convoluted and likely to cause problems.
If a direct wire seems to fix the problem, you may want to look into installing a directly fed relay, and just use the original supply for relay control voltage
 
What about poor connections at harness connectors, in the ignition lock (main switch), kill switch, etc?

I think I mentioned previously that the first thing I checked, once I realized the dead cylinder was intermittently switching sides, was the ignition switch and the wires within the headlight case. I also recut the leads from the coils to the spark plugs. No affect..

Lots of possibility for excessive resistance and voltage drop. Try testing with a direct wire from battery+ to coils+, and see if that fixes it.

Again, difficult to test both because: 1) the problem's both random and intermittent. If everything works with a direct wire is it because of the direct wire or because it's just one of the (random and intermittent) times when both cylinders work?; and 2) I'm limited in how much I can do in a public parking lot (I don't know anyone close by with a garage). But, still, I'll see what I can do.

As I have mentioned numerous times, the original current path (wiring, connectors and switches) from battery + through coils and points to ground is extremely convoluted and likely to cause problems.
If a direct wire seems to fix the problem, you may want to look into installing a directly fed relay, and just use the original supply for relay control voltage

The one option that is NOT an option is modifying the original layout of the bike. I realize there're many ways to improve the XS2 and remedy its many inherent limitations, but my goal is to fix/get the OEM components to work to spec, as I've done for 45+ years, every time I've had to solve one of these perplexing problems. I've got vintage OEM cars that I deal with similarly. But I appreciate where you're coming from (trying to solve the problem).
 
We will find it after a while and with cooperation
If it runs on both sides ( properly ) carburetor and spark and timing is about right
No reason to believe a lacking air supply

I am at a poor power supply or poor ground wiring ..It is the perhaps most common ignition problem
The bypass wiring is helpful in testing which I have had god experiences with.
If a large circuit it can be time consuming and difficult to locate the defect item or wire
and the bypass is at times quicker and safer.
Ensure the right physics into the ignition see if it helps.

But feel free to service it downstream from battery to ignition ..or upstream from spark plugs It can take longer time but is one way to do it also.
intermittent problem can be difficult to find A voltmeter installed can help.
 
We will find it after a while and with cooperation
If it runs on both sides ( properly ) carburetor and spark and timing is about right
No reason to believe a lacking air supply

Agreed. Unfortunately, I spent most of last year and....I believe it was....nine carb rebuilds to get here (you're welcome to read through that very lengthy carb rebuild thread if you're a masochist). It was only after discovering, this past weekend, that the intermittent dead cylinder problem was intermittently switching sides that I finally realized the problem wasn't with the right carb.

I am at a poor power supply or poor ground wiring ..It is the perhaps most common ignition problem
The bypass wiring is helpful in testing which I have had god experiences with.

Did you see the movie On the Beach? If so, something akin to the Coke bottle scene is where my gut's telling me the problem lies. That is, there's something electrical that's either loose (and randomly/intermittently connecting/disconnecting) or failing. Although I'll continue checking, the back-and-forth nature of the dead cylinder tells me it's something electronic rather than static (bad connection/wire)


But feel free to service it downstream from battery to ignition ..or upstream from spark plugs It can take longer time but is one way to do it also.
intermittent problem can be difficult to find A voltmeter installed can help.

I'll take the Fluke with me this weekend so I can check battery volts at various RPMs. Thanks!
 
Had very similar issue on my '81 special ll. Intermitent dead cylynders and backfiring then it would sometimes come back to normal when riding. I suspected everything from carbs to plug wires. Turned out to be a worn ignition (key) switch. The internals were getting loose and not always making solid contact. As your guy says. "A single part shared by both sides on the cusp of failure." Not sure how similar our models are butt it's a possibility. I think sometimes we tend to overthik these problems and overlook the simple stuff.
 
Had very similar issue on my '81 special ll. Intermitent dead cylynders and backfiring then it would sometimes come back to normal when riding. I suspected everything from carbs to plug wires. Turned out to be a worn ignition (key) switch. The internals were getting loose and not always making solid contact. As your guy says. "A single part shared by both sides on the cusp of failure." Not sure how similar our models are butt it's a possibility.

Thank you.
I'm pretty certain we have different ignition switches (mine's a single component sitting by itself between the speedo and tach) and I think yours is part of a module containing gages and turn signals. However, I suspect the actual wiring of the ignition switch and that wiring's path into the ignition circuit is similar.

That guy was me and the ignition switch was the first thing I thought of when I discovered the intermittent dead cylinder was intermittently switching sides. So far, all I did was jiggle the ignition key and wires coming outta the bottom of the switch and into the headlight bucket....jiggling individual wires in the headlight with the engine running to see if anything affected the idle, one way or the other. Unfortunately, no change. So I'm wondering if it's the ignition switch itself?

I think sometimes we tend to overthik these problems and overlook the simple stuff.

That's what I'm saying.
 
Intermitent dead cylynders and backfiring then it would sometimes come back to normal when riding.

I find the bolded part of your comment especially relevant.

Last year, when this all began (and we all thought it was a right-side carb issue likely due to my use of MikesXS rebuild kits for the past 20 years), hence the lengthy carb rebuild thread and nine rebuilds), I mentioned that I thought it was a clue to the source of the idle problem that, intermittently, say, one out of 10 times, if I let the bike sit and idle (poorly) for 15~20 minutes, all of a sudden...like someone threw a switch...the idle would increase ~200 rpm and become perfectly smooth. At that point, I could take the bike out for hours and it'd run perfectly......until I shut it off. Then, it'd be back to luck-of-the-draw to see which, if any, of the cylinders would be dead.

p.s. Did you end up replacing the ignition switch or were you able to disassemble/repair it?
 
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Only two places (electrical) I can think of that would affect both cyls at separate times...
The power wire from the kill switch goes down to the coils. It goes from a single wire to a dual in-line bullet connector that splits it out to both coils. Highly unlikely... but it's possible it's intermittently losing contact on one cyl or the other. Might try crimping it just a little and cleaning it to see if that helps.

The other place would be the mounting of the condenser pack. Both condensers go to ground on the same mounting screw. If it's loose or dirty it could intermittently affect both cylinders.
Those are the only two points I can think of where both ignitions systems have commonality.
 
One option that is NOT an option is modifying the original layout of the bike. I realize there're many ways to improve the XS2 and remedy its many inherent limitations, but my goal is to fix/get the OEM components to work to spec, as I've done for 45+ years, every time I've had to solve one of these perplexing problems. I've got vintage OEM cars that I deal with similarly. But I appreciate where you're coming from (trying to solve the problem).

Well, it would actually be a fully reversible mod, and not involve cutting or modifying the harness or coils in any way. Just a direct power wire from battery to coils +, via a 10A fuse and a standard Bosch relay. This would then either fix your problem or not, while everything operates just as on a stock bike. If it should fix your problem, then you know that the issue is voltage (drop) related, and you can start pulling switches apart, replacing sections of wire, etc.
Frankly, believing you can solve this potential issue, while keeping near 50 years old OEM switches, connectors and wires may not be the best approach. Unless you are able to source immaculate NOS components and parts. Worst case, you can end up having to use reproduction switches etc, if the OEM ones on your Bike are just worn out or corroded. So you may be in Catch-22 situation. Not original or not original.....The suggested "relay mod" is 99% invisible anyway.
Finally, any "electrical check" done without a multimeter (actually volt and ohm meter) is not really telling anything. Measuring coil primary and secondary resistance, then checking voltage at coil + under load (points closed), then voltage drop across points (again closed) is the only way to verify that the ignition circuit is in fact as it should be.
 
Only two places (electrical) I can think of that would affect both cyls at separate times...
The power wire from the kill switch goes down to the coils. It goes from a single wire to a dual in-line bullet connector that splits it out to both coils. Highly unlikely... but it's possible it's intermittently losing contact on one cyl or the other. Might try crimping it just a little and cleaning it to see if that helps.

The other place would be the mounting of the condenser pack. Both condensers go to ground on the same mounting screw. If it's loose or dirty it could intermittently affect both cylinders.
Those are the only two points I can think of where both ignitions systems have commonality.

Thanks. Two good suggestions that make logical sense. I'll trace/check that wiring this weekend when I take the Fluke to check voltages.
 
Finally, any "electrical check" done without a multimeter (actually volt and ohm meter) is not really telling anything. Measuring coil primary and secondary resistance, then checking voltage at coil + under load (points closed), then voltage drop across points (again closed) is the only way to verify that the ignition circuit is in fact as it should be.

That may be a bit beyond my present capabilities (i.e., working on the bike in a public parking lot where only very limited disassembly/rewiring is possible). But I'll see what I can do this weekend.
 
I like @arcticXS 's idea of the relay. And yes, it could be done without changing any of the existing wiring. Would be easy to return it to original at any time.
It's a mod I plan on doing to my SG this winter.
 
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