Intermittent Dead Cylinder...Switching Sides

[gunk]

Hey Freddy .Sorry to hear about your frustrating problem. Just a heads up. this summer I bought 5 boxes of NGK plugs
from a well known distributor I've dealt with for years Both for my RD400 and xs650c. Sometimes quality control problems hit.
Out of the 20 brand new plugs 5 were defective right out of the boxes. No signs of cracked porcelin or damage of any kind.
I was chasing my tail a bit as I automatically ruled out the new plugs. Have also had a new ngk resistor plug cap
that was n.f.g. out of the box . I am not trashing N.G.K. products in any way just to be clear as I have used their stuff for over 40 years before encountering this. I now ground each and every new plug on the fins and check for spark before threading them in. Found one more new defective one that way. Perhaps a new manufacturing plant somewhere or something I'm unaware of in the manufacturing process. Try slowly pulling the sparkplug cap up from the plug on the dead cylinder while the bike is running. Gloves would be a good bet to avoid a lifter. That's how I found the defective plug cap. The bike started to run on both cyls. when the cap was almost off the plug. Swapped the plugcap and the problem was gone. Also after checking all the wires and taking the advice of all the great folks trying to help out. Have You tried running it with the tank off the bike?
Sometimes over the years and owners wiring shifts ,moves,gets routed differently, chafes through and installing the tank can initiate said intermittent short when adding in engine vibes.Good luck.

 

[freddy3]

Out of the 20 brand new plugs 5 were defective right out of the boxes.

Thanks, but I'm ahead of you. I replaced the plugs last weekend. No change.
I'm pretty well convinced the source of the problem's a single component that feeds both cylinders. That said, I have another new set of plugs (Champion?) that I'll try next weekend, just to say I've turned over every stone I'm able to handle in a public parking lot.
Thanks again for the input.

 

[freddy3]

Try slowly pulling the sparkplug cap up from the plug on the dead cylinder while the bike is running....That's how I found the defective plug cap. The bike started to run on both cyls. when the cap was almost off the plug. Swapped the plugcap and the problem was gone.

That's exactly how I discovered the dead cylinder switching sides.
First, I realized that when I blipped the throttle of the left carb, the engine speed increased normally. When I did the same to the other carb, the engine went flat. Not a stall, but the idle dropped and it gurgled for a bit before the engine speed slowly chugged back up. That tended to support what I'd thought over the past year—carb problem. So I turned the engine off, pulled the carb cover off to check for leaks, crimped diaphragm, circlip on wrong notch of the needle, etc. All okay.
I restarted the bike and blipped the left carb. The idle glugged and the engine went flat. Just like it did when I previously blipped the other carb. So I blipped the other, previously flat carb and the engine speed increased normally. That's the point at which I realized the problem was switching sides. At that point, I tried pulling the spark lead off the flat-spot side--no effect. When I pulled the other side's spark plug lead, the engine stopped. So, obviously, the problem all along has been that one cylinder was not running, and the non-running cylinder was randomly switching sides.
Anyway, I think you can see where this's heading..

Have You tried running it with the tank off the bike?

Yup. A few times, when I was checking/jiggling wires around the ignition switch, headlight case, coils and spark plugs to see if messing with anything down there had an effect on the idle speed (it didn't).

 

[gunk]

How old is Your fuel? Is the bike stored in a cold garage where water can accumulate in ethanol based gas? Possible sediment in the tank and or fuel taps. Do You have inline fuel filters? Go to the very start of Your fuel supply and work
through the easy most obvious stuff first. I've learned that one the hard way over thinking a problem sometimes over the years.
Just a suggestion. Sure hope You have some good luck soon.

 

[Jan_P]

Blipping the throttle and stalling is consistent with weak spark aka Low Voltage
On my 80 one cannot blip one carburetor they are connected.
Please describe in what position the non blipped 2 carburetor is in
when the other 1 is blipped .
If I get this right the blipping 1 will increase the rev but with a non corresponding butterfly valve position on the non blipped 2 side
I am not sure i am thinking right here but the pistons move and the non blipped 2 is closed .. less air flow but the same suction pressure
Can throw off mixture apologize if I am lost here it is late ..

Sorry if I don't get this but i am thinking in terms of a weak spark and the blipping of the other side throws off the mixture
and the weak spark cant handle it

 

[freddy3]

How old is Your fuel? Is the bike stored in a cold garage where water can accumulate in ethanol based gas? Possible sediment in the tank and or fuel taps. Do You have inline fuel filters? Go to the very start of Your fuel supply and work
through the easy most obvious stuff first. I've learned that one the hard way over thinking a problem sometimes over the years.
Just a suggestion. Sure hope You have some good luck soon.

Thanks, but the fuel's new (tried with and without carb cleaner or Seafoam) and I've got good flow to each carb and between each float bowl. The fuel lines were checked each time the carbs were rebuilt last year (i.e., nine times).

 

[freddy3]

Blipping the throttle and stalling is consistent with weak spark aka Low Voltage
On my 80 one cannot blip one carburetor they are connected.
Please describe in what position the non blipped 2 carburetor is in
when the other 1 is blipped .
If I get this right the blipping 1 will increase the rev but with a non corresponding butterfly valve position on the non blipped 2 side
I am not sure i am thinking right here but the pistons move and the non blipped 2 is closed .. less air flow but the same suction pressure
Can throw off mixture apologize if I am lost here it is late ..

Sorry if I don't get this but i am thinking in terms of a weak spark and the blipping of the other side throws off the mixture
and the weak spark cant handle it

Our carb setup is different. I believe the two carb throttles are linked to each other on yours. So blipping one carb blips them both.
On the XS2, the carb throttles are linked only by the throttle cable coming from the handlebars. The actual throttle shaft in each carb operates independently. So, with the engine running, I can blip one carb without affecting the other carb. And doing exactly that is how I came to find that: 1) the carb on the non-running cylinder had a flat spot when I blipped it; and 2) the carb with the flat spot followed the dead cylinder. That is, the flat spot when I blipped the carb's throttle was NOT the problem; the flat spot resulted in a cylinder that wasn't firing. Point being that, all last year, we all had the source of the problem pegged to the carb, when, in fact, the flat spots in the carb was the result of the dead cylinder.

I don't know if that makes sense, but, put simply: when I blip the throttle shaft of the running cylinder, the rpms increase (like they should). But when I blip the throttle shaft of the non-running cylinder, the rpms DEcrease (denoting a problem). The flat-spots are NOT the problem, they're just the result of that cylinder not firing when its carb is blipped.

 

[freddy3]

Doesn't the kill switch feed both cylinders?

 

[Jim]

Doesn't the kill switch feed both cylinders?

Yes. So does the ignition switch.... so does the battery. none of the 3 could affect cylinders separately.

 

[freddy3]

Yes. So does the ignition switch.... so does the battery. none of the 3 could affect cylinders separately.

There're two separate coils and, from there, each cylinder has its own discrete ignition line to the spark plugs. So, at some point between the ignition- and handlebar kill-switches, the ignition circuit must branch from a single component (e.g., ignition- or kill-switch) into the two discrete lines (to the coils). No?

 

[Jim]

There're two separate coils and, from there, each cylinder has its own discrete ignition line to the spark plugs. So, at some point between the ignition- and handlebar kill-switches, the ignition circuit must branch from a single component (e.g., ignition- or kill-switch) into the two discrete lines (to the coils). No?

Power is a single wire from the battery to the iggy switch, single wire to the kill switch and single wire to the coils. At the coils is a double bullet connector where you plug the coils into the single wire. Back in comment #34....

 

[Jan_P]

Our carb setup is different. I believe the two carb throttles are linked to each other on yours. So blipping one carb blips them both.
On the XS2, the carb throttles are linked only by the throttle cable coming from the handlebars. The actual throttle shaft in each carb operates independently. So, with the engine running, I can blip one carb without affecting the other carb. And doing exactly that is how I came to find that: 1) the carb on the non-running cylinder had a flat spot when I blipped it; and 2) the carb with the flat spot followed the dead cylinder. That is, the flat spot when I blipped the carb's throttle was NOT the problem; the flat spot resulted in a cylinder that wasn't firing. Point being that, all last year, we all had the source of the problem pegged to the carb, when, in fact, the flat spots in the carb was the result of the dead cylinder.

I don't know if that makes sense, but, put simply: when I blip the throttle shaft of the running cylinder, the rpms increase (like they should). But when I blip the throttle shaft of the non-running cylinder, the rpms DEcrease (denoting a problem). The flat-spots are NOT the problem, they're just the result of that cylinder not firing when its carb is blipped.

Bare with me on this one
The left side and right side are coupled i write it here so perhaps I get it
2 carburetors L and R
Bike is Idling
Blipping L not R ---> So, with the engine running, I can blip one carb without affecting the other carb
Now when blipping L a lot of things happen the L cylinder spools up and revving increasing air flow L and advancing Ignition
But that increased Airflow cant happen on R since the R is not blipped it is still in the idle position essentially closed butterfly valve
how that affects the mixture can be a doctoral thesis ..The engine is Coupled mechanically via the Crankshaft .
R is trying to push through the same amount air ..but i cannot since the butterfly valve is closed .What that means in mixture is difficult.
If I should guess there is a slowing of air speed and a pressure change on the downside of the Butterfly valve ( Butterfly Valve at Idle position but the bike is spooled up via L )

1) the carb on the non-running cylinder had a flat spot when I blipped it;

I read this as then after blipping the L you then try to blip the R that now via the L blipping is in a who knows state .The mixture loaded into the cylinder and carburetor can have taken a hit so to speak Level in floats can be off and mixture in cylinder can be off Over rich
Then it can off course behave erratically. It needs to get the air flowing to fill up bowls flush out the Extra fuel and starting burning off fuel and soot off the plug- And after a while it gets back to normal .. ( if settings and spark is OK )

2) the carb with the flat spot followed the dead cylinder is this the same cylinder aka the one with the mixture history Off
the flat spot resulted in a cylinder that wasn't firing

when I blip the throttle shaft of the running cylinder, the rpms increase (like they should). But when I blip the throttle shaft of the non-running cylinder, the rpms DEcrease (denoting a problem). The flat-spots are NOT the problem, they're just the result of that cylinder not firing when its carb is blipped

HERE IS WHERE I AM AT

when I blip the throttle shaft of the running cylinder, the rpms increase -NORMAL --> but at the same time it messes up the mixture on the other side pressure and flow conditions are not in sync with that cylinders /carburetors airflow and of course affects combustion

If then let go on L and tries to blipp R --> But when I blip the throttle shaft of the non-running cylinder, the rpms DEcrease (denoting a problem)

I am thinking in terms of over rich or even droplets in that cylinder .Because the blipping on the other side
condensed on the Plug and when air comes in , blipping it takes a while to get to normal And perhaps getting R to respond but now " filling up " L

Now this malfunction on a cylinder is more sensitive when the spark is weak :Over rich and weak spark will stall if applying throttle
If kept even it can run longer as those with an open circuit rotor can notice. Soft hand on the throttle you can get home
But if you give throttle it stops there and then .It can start again If doing it right.

Sorry if I got this wrong point being that the carburetors are still coupled in working point via the Crank and Airflow

I actually looked at the Wiring schematic and Jim has a Good point there in the # 34 that is something to check
the split one into two.

But I am still at a Voltage supply Problem .. Keeping the carburetor butterfly's L and R at the same angle as in the never models
And getting the Voltage up on the ignition Will fix it I do believe

 

[freddy3]

I actually looked at the Wiring schematic and Jim has a Good point there in the # 34 that is something to check
the spit one into two.
But I am still at a Voltage supply Problem .. Keeping the carburetor butterfly's L and R at the same angle as in the never models
And getting the Voltage up on the ignition Will fix it I do believe

Agreed. I think we've all been overthinking this. But it was only after I discovered, this past weekend, that the flat-spot in whichever carb was idling rough wasn't due to a problem within that carb, but, rather, a problem elsewhere. That flat-spot blipping discovery, made only last weekend, then led me down an entirely different path than the one that virtually everyone who contributed to the lengthy (and repeated) carb rebuilding thread from last year was on. Then, once I found that the flat-spot/blipping issue switched sides, it was only then that I concluded the carbs were not the problem.....having spent the last year-and-a-half focused exclusively on the right-side carb as the source of the rough-running. And once I found that pulling the spark plug lead on the rough-running side had NO effect on the idle AND that, intermittently, the problem switched over to the other side.....well, what appears more or less obvious today wasn't so obvious without knowing two NEW facts (i.e., the problem affects BOTH sides and it's electrical rather than fuel).

Anyroads, when I make the trip out to the bike this weekend, I'll concentrate on the ignition and kill switches along with their wiring/grounds and see if they're able to be disassembled/cleaned/checked without too much ado (since I cannot perform alot of disassembly work in a public storage parking lot).

Thanks again.

p.s. Here's a screenshot from last year's carb rebuilding thread that illustrates how the clue was staring us all right in the face, but we completely missed it.

 

[Jim]

I'll concentrate on the ignition and kill switches along with their wiring

Again.... the kill switch has a power wire in and a power wire out... a single lead. Unless someone can explain to me how one wire can individually single out separate components, I'll continue to suggest your problem... if it is electrical, has to have commonality with both ignition systems AND the ability to single out one or the other. A single wire or a single pole switch doesn't have the ability to do that.
From what you've said, you're lacking in proper facilities (storage shed) and time. I'd suggest not wasting that time checking stuff that isn't physically capable of causing your problem.

 

[freddy3]

Again.... the kill switch has a power wire in and a power wire out... a single lead. Unless someone can explain to me how one wire can individually single out separate components, I'll continue to suggest your problem... if it is electrical, has to have commonality with both ignition systems AND the ability to single out one or the other. A single wire or a single pole switch doesn't have the ability to do that.
From what you've said, you're lacking in proper facilities (storage shed) and time. I'd suggest not wasting that time checking stuff that isn't physically capable of causing your problem.

Simple question: What component(s) on a 1972 XS2 carries both left and right ignition circuits?

 

[Jim]

Simple question: What component(s) on a 1972 XS2 carries both left and right ignition circuits?

The simple answer is the entire power distribution system from the battery all the way to the coil(s) bullet connector.
But your simple question isn't the full question. The full question is "What component(s) on a 1972 XS2 carries both left and right ignition circuits and have the ability to selectively, separately. and randomly cause one or the other ignition systems to fail?"
The answer to that two part question is simple and I've given it to you 3 times now in comment 34, 51 and 54.... the bullet connector where power splits from a single wire out to two separate wires to the coils.
You don't have to take my word for it, you can see the affects yourself. Disconnect the red/w wire from the kill switch. What happens? the bike dies 'cause BOTH coils lost power.
Now, at the coil bullet connector... pull one of the coil wires out... either one.. doesn't matter. What happens? That cylinder dies... and ONLY that cylinder because it's the only one that lost power.
This is my 4th explanation now... not sure how much more clear I can be.

 

[Jan_P]

I am gonna stick my neck out here
When you get to the bike start it up ..
Start
Measure the charging voltage across the battery I believe it is low
The shifting right to left and left to right I believe is the non synced blipping one side at a time flooding one side and stalling because of the rich mixture and weak spark

 

[Jim]

Measure the charging voltage across the battery I believe it is low

I don't know about charging (not really able to check it), but the battery's fully charged.

 

[freddy3]

Measure the charging voltage across the battery I believe it is low
The shifting right to left and left to right I believe is the non synced blipping one side at a time flooding one side and stalling because of the rich mixture and weak spark

I'll have the Fluke with me when I go this weekend, but from post 15: "The last time I checked it, I think the volts were ~14-ish at idle (when both cyls were firing) and, yes, the lights brightened when the engine's revved. It's ALWAYS done that (I've owned the bike since '75)."

 

[freddy3]

The simple answer is the entire power distribution system from the battery all the way to the coil(s) bullet connector.....

True, but isn't much of that distribution system dedicated to charging and other non-ignition-related electrical functions?
Presuming similar engine rpms, I've seen no difference in the brightness of the headlight (beyond the general brightening of the headlight when the engine's revved as it's done since I've owned the bike) between the times when the engine's running rough (i.e., on one cylinder) and when it's running smooth (i.e., on both cylinders). But, again, I'll have the Fluke with me this weekend to check volts.

Now, at the coil bullet connector... pull one of the coil wires out... either one.. doesn't matter. What happens? That cylinder dies... and ONLY that cylinder because it's the only one that lost power.

I get that and I'm not questioning or disagreeing with that. As I said, I'll check the wiring/connectors ahead of the coil again this weekend.
'Til then, I'm not trying to be argumentative, but please understand that, after more than a year spent chasing ghosts, I'd rather understand exactly how and why something may be contributing to the problem rather than just trying any and everything suggested.....which is what I did all last year to no avail.

Again, to be clear, I'll be checking those bullet connectors along with the rest of the ignition-related circuitry ahead of the coils (where the circuitry divides into two) this weekend. If there's something I missed elsewhere in this thread, just understand that I was already overwhelmed with this last year....So, please take that into consideration.