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Because it's misfiring on one cylinder, then turning back on - like kid playing with light switch.

First let me say that I am no guru when it comes to carbed engines.


But when you say that its misfiring on one cylinder - of course it is - its a wasted spark system and only one cylinder fires at any time from the same, dual output coil. The problem is, how can you tell, from the video clips, whether its the same cylinder every time?



If Ignition pick-up or ignition computer it would be both cylinders cutting out or randomly switching from side to side

Personally I tend to think that the misfire is randomly switching from side to side, since the pickup, ignition coil and igniter unit are all common to both cylinders.



The ignition coil may test OK cold, but when it gets hot, problems show up.

I agree, the main suspect would be the coil or its HT cables. The igniter units are far less forgiving and would tend to cut the engine completely as load on it increased. As for the pickup coil, I guess that an incorrect air gap could cause these symptoms but apart from that, experiences on here show that the pickup coil goes open circuit and cuts both cylinders until it cools down again.
 

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Is the miss only on one cylinder, the same cylinder always? If so remove the right plug wire from the plug and cross it over to the left and left wire to right plug. If the skip moves to the other cylinder it's the coil or wire. If not carb-fuel air problem.
 

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But when you say that its misfiring on one cylinder - of course it is - its a wasted spark system and only one cylinder fires at any time from the same, dual output coil. The problem is, how can you tell, from the video clips, whether its the same cylinder every time?
You are right, I can't tell from the video if it is only one side failing but there were a couple of other clues

<<What already been done:
New air filther
New CDI (triumph twin power Stage 1) ---> really, on a carbed bike??
New Sensor ---> so he changed the pick up coil already??
New Spark plugs
Carbs cleaning and synchronization >>

So the only thing he didn't change was the HT coil.

Also when the coil on my carbed bike failed it was definitely one side only. His actually sounds like a partial failure on one side. But when it goes, it's the worst performing single cylinder bike you've ever ridden.

Somewhere i think i saw that the coil is like a center tap device so half of the coil fires the right side and the other half the left. both at the same time. So a failure (open circuit or ground out) will just stop half the circuit from working. It can be fine cold and bad hot.

Wasted spark is fine. While one side is on the compression stroke ready to fire, the other is pushing exhaust gas out and under normal conditions, having that plug firing does nothing, but it does makes the ignition circuit simpler.
 

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New CDI (triumph twin power Stage 1) ---> really, on a carbed bike??



Yes, I presume its the TTP Fire Starter. The igniter is like a very simple ECU which takes care of the basic things like ignition advance (stage 1). The igniter has the capacity to fire up to 4 individual coils and also sends out data to the rev counter. The ECU on EFI models handles a lot more, such as engine sensors (MAP, safety interlocks, fuel injectors etc).



So the only thing he didn't change was the HT coil.

Yes I guess that would work in a process of elimination.


Somewhere i think i saw that the coil is like a center tap device so half of the coil fires the right side and the other half the left. both at the same time. So a failure (open circuit or ground out) will just stop half the circuit from working. It can be fine cold and bad hot.

The coil is not centre tapped, the secondary is merely one winding with a spark plug on each end. When the field breaks down inside the coil, the spark energy travels down the HT cable of the cylinder firing, jumps the plug gap, firing that cylinder, then through the cylinder head casting and fires the other plug in reverse direction - which means the wasted spark jumps from the plug's 'L' terminal across to the centre electrode, then back into the coil, completing the circuit.


I have no idea what determines the direction of the spark energy, all I know is that one cylinder will spark from centre electrode to the 'L' tab on the plug, the other cylinder sparks in reverse.



The wasted spark method is just to cut down on production costs and save space (only 1 coil instead of 2). It is an amazingly clever idea but logically it also means that if there should be any kind of break in the continuity, both cylinders suffer the consequences. I guess its possible for the engine to fire only on one cylinder if the coil is still working, perhaps by one of the HT cables arcing out or a similar fault.
 

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The coil is not centre tapped, the secondary is merely one winding with a spark plug on each end. When the field breaks down inside the coil, the spark energy travels down the HT cable of the cylinder firing, jumps the plug gap, firing that cylinder, then through the cylinder head casting and fires the other plug in reverse direction - which means the wasted spark jumps from the plug's 'L' terminal across to the centre electrode, then back into the coil, completing the circuit.


I have no idea what determines the direction of the spark energy, all I know is that one cylinder will spark from centre electrode to the 'L' tab on the plug, the other cylinder sparks in reverse.



The wasted spark method is just to cut down on production costs and save space (only 1 coil instead of 2). It is an amazingly clever idea but logically it also means that if there should be any kind of break in the continuity, both cylinders suffer the consequences. I guess its possible for the engine to fire only on one cylinder if the coil is still working, perhaps by one of the HT cables arcing out or a similar fault.

I wonder what sort of spark plugs the OP installed?


AFAIK with the wasted spark method the spark reverses polarity/direction every time it fires and the same material is needed on both sides of the gap so it fires the same no matter its polarity.


if single tipped platinums are used in a wasted spark system they soon misfire. that's why double tipped platinums need to be used for wasted spark systems. I presume the same would be for iridium


personally I just use conventional copper plugs and change them out when specified. I think for these it is meant to be 20,000 Kilometers, but I once inadvertently left them in for 40K and had no probs.
 

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AFAIK with the wasted spark method the spark reverses polarity/direction every time it fires and the same material is needed on both sides of the gap so it fires the same no matter its polarity.
if single tipped platinums are used in a wasted spark system they soon misfire. that's why double tipped platinums need to be used for wasted spark systems. I presume the same would be for iridium
"Wasted spark" simply means both spark plugs fire at the same interval, In the case of a twin with a 360 degree firing
order, the plugs fire with one cylinder at the end of the compression stroke and the other cylinder at the end of the
exhaust stroke (the wasted spark).

The type of spark plug used is irrelevant.

There is no reversal of polarity, each spark plug fires normally every 360 degrees.

When the I-4 engines made their way into motorcycles in the '60s, they used wasted spark as well.
Typically they were set up as a pair of 360 degree twins........one dual wire coil firing the spark plugs of cylinders 1 & 4,
the other firing cylinders 2& 3.

When the 6 cylinder machines appeared in the late '70s, (Honda CBX and Kawasaki KZ13000) they used wasted spark
as well. They were set up as a trio of 360 degree twins........one dual wire coil firing the spark plugs of cylinders 1 & 6, another firing cylinders 2 & 5, and the third firing cylinders 3 & 4.


Rex
 

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The coil is not centre tapped, the secondary is merely one winding with a spark plug on each end. When the field breaks down inside the coil, the spark energy travels down the HT cable of the cylinder firing, jumps the plug gap, firing that cylinder, then through the cylinder head casting and fires the other plug in reverse direction - which means the wasted spark jumps from the plug's 'L' terminal across to the centre electrode, then back into the coil, completing the circuit.

I have no idea what determines the direction of the spark energy, all I know is that one cylinder will spark from centre electrode to the 'L' tab on the plug, the other cylinder sparks in reverse.
You will need to explain to me how electricity knows where to go (and where not to go) once it has reached ground for me to believe that one :) Super high voltage drives the spark from the center electrode to the ground and the voltage is dissipated doing that.

Your explanation suggests only half the voltage goes away and that magically goes thru the ground circuit without blowing any fuses, or melting any wires to re-appear at the one most difficult path for the voltage to follow - the second plug gap - and then jump across there because it wants to. Sorry, but that makes no logical sense.

Here is an ignition diagram for my 4 cylinder wasted spark Suzuki - the bonnie only needs one coil not the 2 shown here. And Triumph didn't put a similar pic in their manual, other wise I'd show that one.
Note all the spark plugs go to ground, I guess it doesn't need to be center tapped, but after the failure, I never changed the plug leads or plugs, just the coil and it worked again.

[/url][/IMG]
 

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You will need to explain to me how electricity knows where to go (and where not to go) once it has reached ground for me to believe that one :) Super high voltage drives the spark from the center electrode to the ground and the voltage is dissipated doing that.

For clarity, lets assume that #1 cylinder is firing and #2 cylinder is at the top of exhaust stroke, or 'on the rock'. The super high voltage you speak of is in the order of 20 - 30,000 volts.



The spark current does not see ground, it simply follows the path of least resistance to complete its circuit, which is through the head casting and #2 spark plug gap.


Your explanation suggests only half the voltage goes away and that magically goes thru the ground circuit without blowing any fuses, or melting any wires to re-appear at the one most difficult path for the voltage to follow - the second plug gap - and then jump across there because it wants to. Sorry, but that makes no logical sense.

I'm not very good at explaining these things, I find it very difficult to put into words but the spark current does not 'go away'. It jumps both plug gaps to complete its circuit and ignites #1 cylinder on its way through. Igniting the fuel does not 'use up' the spark current, it simply uses the heat generated by the ionized air in the plug gap. The spark energy is dissipated in the coil when the circuit completes.



As I said I am not good at detailed explanations such as this, so I scoured the net (read Google) to find the diagram below which shows how the wasted spark works. With the greatest of respect, should you need to know any more, please ask Mr Google.




I have to say that Bonza was spot on in his theory about plugs. When the spark jumps the gap it takes material with it (spark erosion), so in the above diagram, plug#4 would lose material from its centre electrode and plug#1 would lose material from its side, or 'L' electrode (since Faraday was proven wrong - electrons travel from negative to positive). Therefore the electrodes of the plugs need to be made of a metal which is resistant to the erosion such as iridium or platinum, although most are plain steel and changed more regularly.
 

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"Wasted spark" simply means both spark plugs fire at the same interval, In the case of a twin with a 360 degree firing
order, the plugs fire with one cylinder at the end of the compression stroke and the other cylinder at the end of the
exhaust stroke (the wasted spark).

The type of spark plug used is irrelevant.

There is no reversal of polarity, each spark plug fires normally every 360 degrees.

I here what you say. I did not explain myself properly


I do know what wasted spark is. the spark plugs fire every 360 degrees which includes near top of the exhaust stroke, hence the spark is "wasted"


I mentioned reversing of polarity with each firing as one of my cars (2005 Jeep Wrangler) uses the wasted spark method and it certainly does reverse polarity. this is discussed a lot on Jeep forums. many Jeepers upgrade from normal conventional copper to platinum plugs and soon misfiring occurs. in this vehicle double tipped platinums must be used and not single platinums otherwise the electrode quickly erodes and misfires occur


whether Triumph Bonnevilles have their polarity reversed with every fire, I dunno


but I noticed the op mentioned that the plugs were replaced hence my question what plugs were put in, especially many riders use iridiums and I would imagine the same applies to them as platinums
 

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You will need to explain to me how electricity knows where to go (and where not to go) once it has reached ground for me to believe that one :) Super high voltage drives the spark from the center electrode to the ground and the voltage is dissipated doing that.

Your explanation suggests only half the voltage goes away and that magically goes thru the ground circuit without blowing any fuses, or melting any wires to re-appear at the one most difficult path for the voltage to follow - the second plug gap - and then jump across there because it wants to. Sorry, but that makes no logical sense.
The HT secondary finishes up, when the LT primary coil's field collapses, with a large positive voltage at one end of the coil and a large negative voltage at the other. These voltages both jump the spark plug gaps to ground, rather than going running round via ground to each other.
 

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For some reason the diagram has not appeared in my previous post so I have tried attaching it.
 

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The spark current does not see ground, it simply follows the path of least resistance to complete its circuit, which is through the head casting and #2 spark plug gap.
The cylinder head is grounded. The engine is a conductor and there is a large cable at the back of the engine that runs up to the Neg on the battery. So yes It does see ground. The engine is not rubber mounted, it is bolted to the frame - more ground points. Very hard to stop the engine from seeing ground. Hence the expressions "ground the plug out against the head", "time to fix the grounds on the engine" etc.

Schematics can be confusing as they don't necessarily show reality, just how the electricity is supposed to flow and the simplified components in the system.

Electricity is often compared to water flow so lets think about this as a hydroelectric dam.
The water behind the dam is the potential (voltage). It runs down a pipe, thru a turbine to make electricity and the water runs out in the river below. Which I'm calling zero potential, or ground. If you have 2 pipes you can turn 2 generators etc. (2 spark plugs) or even 1 pipe splitting into 2 pipes.

With your scheme, you would need a pump at the bottom of the dam to pump the water back up to the top and that pump would take more electricity that what was just generated. So no it doesn't work.
But if you could, this would be the equivalent of another "coil" at the bottom firing backwards thru the plug. Bike just doesn't have that it has one coil.
If you put 10-15KV thru an engine, people would be electrocuted. That isn't happening either. Ever put your hand on a damaged plug lead? I have, it's very noticeable!!!!!
 

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The cylinder head is grounded. The engine is a conductor and there is a large cable at the back of the engine that runs up to the Neg on the battery. So yes It does see ground. The engine is not rubber mounted, it is bolted to the frame - more ground points. Very hard to stop the engine from seeing ground. Hence the expressions "ground the plug out against the head", "time to fix the grounds on the engine" etc.
Its not a matter of the engine seeing ground because it IS the ground plane of the bike, frame included. Its the spark current that does not see ground. This has nothing to do with ground and I have no way of explaining it better to you.

Schematics can be confusing as they don't necessarily show reality, just how the electricity is supposed to flow and the simplified components in the system.
After so long in hobbyist electronics I don't find schematics confusing any more. The schematic is just a representation, but its a representation of reality. Anyway here's some more evidence to back me up.
http://www.crypton.co.za/Tto know/Ignition/wasted sp.html
Electricity is often compared to water flow so lets think about this as a hydroelectric dam.
No, lets not. That is your theory. You asked me in an earlier post to explain mine, which I have done and provided some evidence to support it. Now you provide me with some, backing up what you say.
I love these debates and am always ready to change my way of thinking when proven wrong - that is how I learn and that's a constant process. But getting hung up on this point, however interesting it may be, is beginning to hijack the thread and the OP's bike is not getting fixed. So let's put this to bed, either way, as quickly as possible.
 

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^^^^^^^^^^ watching this with interest

going by the above link that explains "wasted spark" it would seem that there is a reversal of polarity?

as the “exhaust sparks” have much lower voltage flowing as there is no need for high energy to bridge the spark plug gap. i.e. no compression. As we said before they also are of opposite (negative) direction to the “power sparks” (positive).

Pingwist hasnt responded lately, I wonder if he has it sorted?

to me it sounds like a dodgy coil. you can get PVL coils on ebay from Germany
 

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going by the above link that explains "wasted spark" it would seem that there is a reversal of polarity?
Only in the sense that the spark energy goes through the second plug in reverse direction, this is what they refer to as positive and negative firing. Also from the link:


"That is the spark “flows” from the center to the outside electrode in the one spark plug and from the outside electrode to the center in the second spark plugs."


In order for the spark to jump from the outside electrode to the centre electrode, the spark energy can only originate from one place - the cylinder head casting.

Pingwist hasnt responded lately, I wonder if he has it sorted?

to me it sounds like a dodgy coil. you can get PVL coils on ebay from Germany
I've wondered the same, and whether he thinks the thread has gone so far off the rails in debating this educational but unimportant point that he doesn't think it worth responding. Personally I'm thinking that it may be something else but closely related to the coil, such as a cable or plug cap, or even the cable's connection to the coil, something like that. Another scenario is that the fault could be the coil itself, if the secondary winding has a break in it, the spark energy would jump that gap too, but would be unreliable. Its also worth noting that Pingwist said the engine runs fine at a higher rpm. As the rpm increases the spark energy gets stronger.
 

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Its not a matter of the engine seeing ground because it IS the ground plane of the bike, frame included. Its the spark current that does not see ground. This has nothing to do with ground and I have no way of explaining it better to you.

After so long in hobbyist electronics I don't find schematics confusing any more. The schematic is just a representation, but its a representation of reality. Anyway here's some more evidence to back me up.
http://www.crypton.co.za/Tto know/Ignition/wasted sp.html

After 50 odd years of working as a mechanic I find the schematic as well as the "evidence" to be contrary to everything I've ever been taught or experienced about electrical theory and practice.
I don't claim to be an electrical Guru, but I believe in this case your theory is waaaay off base.


Rex
 

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I don't claim to be an electrical Guru, but I believe in this case your theory is waaaay off base.
And that's fine Rex, no one is holding a gun to your back, As for me, this is what I have been taught and is what I will stick with until it is proved wrong. I've been into all fields of electrics/electronics since the early 70s and haven't stopped learning new stuff yet. Information on this particular subject is very thin on the ground, but all the info I have found says the same.
 

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Well, Ripper, you are probably correct and I am wrong.

Found this page which explains more than you can shake a stick at about ignition systems

https://www.hella.com/techworld/us/Technical/Car-electronics-and-electrics/Ignition-coil-2886/

The systems they show have a high voltage diode in the output, that would only allow the elctrickery to flow one way.
So yes, one of the plugs will flow backwards if Gill put one in the circuit - can't find any details of that construction though.

The page gets into a lot of diagnostics too - section 4, practical tip is interesting - suggests systems can be built with or without the diode
 

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The spark goes one way in one plug and the other way in the other plug. That's because in one plug the centre electrode is very negative with respect to the earth electrode, in the other plug the centre electrode is very positive. That diode in the diagram that RichBinAz found is a spark suppressor, it's there to prevent spurious sparks rather than an essential part of the spark-producing process itself.
 
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