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[Dennis C]

Thack says


"So, what do you think is wrong with that argument, Dennis?"

Sorry I didn't realize it was an argument, but as anyone with electronic knowlege knows if you put two identical circuits in parralell then they both get the same voltage from the supply, put the same two circuits in series then each only gets half the voltage I guess this is the rule you are applying here, but that is not the case, to get a spark voltage of 9kv at any one of the gaps then the same 9kv has to pass through the entire circuit including the other gap, think about it, it can't pass one point at a low voltage and arrive at a higher voltage.

Thack previously said

"The problems arise when it becomes a "willy-waving" contest, and we stop listening to each other. I'm as guilty as anyone of that."

This is were I drop out of this thread as my willy is not up to the contest.

Have a great Christmas and a very happy new year everyone.

[Thack]

Hey, Dennis, don't be daft! The term "argument" wasn't in the sense of "We're having an argument", it was in the sense of a debate, where each participant puts forward an argument for consideration by the others.



We agree that the spark gaps are in series, but volts don't "pass through" something, they are "developed across" something. It's current that passes through things.



So the same current passes through each element in the circuit, and each element develops a voltage across it proportional to its resistance and the current flowing.



I bet you remember from school: Kirchoff's Voltage Law says that the voltages developed across the individual components add up to the voltage applied to the circuit as a whole.

[Norm]

I can't see any need for any of this after all we are only talking about an Enfield built in India, it aint some super bike needing critical ignition and timing

[Thack]

Completely agree with you there, Norm.



The only purpose in discussing it is that - by testing each other's ideas - we might between us approach the truth and learn something we didn't know before. It's an age-old tradition that goes back to the Ancient Greeks, possibly earlier.



I'm feeling a bit sad, now, because it seems like most people really dislike having their ideas tested in debate and I appear to have offended at least one person, possibly more. And yet all I've done is put forward counter-arguments and invited people to test them.



Perhaps for many people this forum isn't about learning stuff, but rather about showing off how much you "know". Learning stuff is much more difficult, especially if it means publicly letting go of previous misconceptions. Admitting you were wrong about something is tough, but you've gotta get used to it if you hope to learn anything.

[Norm]

Thack I don't need to learn anything else, I'm still married to my wife.

[Dennis C]

Perhaps I should explain my reasons for dropping out of this thread

Thack in your first post you said, QUOTE "I'm sorry I can't be of much help, but honestly I wouldn't trust anyone except BB themselves on this one."

In your second post you said, QUOTE "Hey, Norm, that's useful to know, because it's real experience instead of just speculative ramblings from me! "

In you third post you said, Quote "This makes no sense at all. There is absolutely no reason why one plug "breaking down" should "grossly" affect the ignition timing on the other! There might be a tiny difference in the voltage rise-time, but that would be measured in microseconds, if it exists at all.".

In your fifth post you said, QUOTE "I thought I'd take a look on Wolfram Alpha for some more information on spark plug firing voltages. It gives a formula into which I've plugged some numbers.

Also stated in the same post, Quote "For what it's worth, at college we measured the spark voltage on a Honda CB500 at idle, and it was a shade over 6kV, so I guess we're in the right ballpark. "

Now down to post eight you post a nice graph and state, QUOTE "I took this trace from a Honda CB500R last week.", What a strange coincidence.

On page two your first post, Quote "I bet you remember from school: Kirchoff's Voltage Law says that the voltages developed across the individual components add up to the voltage applied to the circuit as a whole. Sorry wrong. Kirchoff's voltage law is as follows. "This law is also called Kirchhoff's second law, Kirchhoff's loop (or mesh) rule, and Kirchhoff's second rule. The principle of conservation of energy implies that. The directed sum of the electrical potential differences (voltage) around any closed network is zero, or: More simply, the sum of the emfs in any closed loop is equivalent to the sum of the potential drops in that loop, or: The algebraic sum of the products of the resistances of the conductors and the currents in them in a closed loop is equal to the total emf available in that loop"

I worked as an electronics engineer all my working life so please don't think you can baffle me with figures and laws and graphs you probably pulled off the internet.

You went from a person speculating what may or may not be to a guru af all thing spark related in just seven days that is really some acheivment.

[Dennis C]

ChrisD, If you are still reading this and not lost the will to live. I would like to apologise for what has happened to you thread.

I hope you soon have a correctly running bike. All the best Dennis.

[Thack]

Crikey, Dennis, that is quite some attack! Although no sane person will still be reading this thread, I hope at least you will read my response and consider it.



I'm not entirely sure what point you are making by giving all those quotations, all of which I stand by and seem entirely reasonable. I wonder if this is a clue:



You went from a person speculating what may or may not be to a guru af all thing spark related in just seven days that is really some acheivment.



In fact I'm 57 years old and have spent almost all of my career in the telecommunications industry, several years of which were as an electronics engineer, and the last 16 years of which were at BT's R&D facility at Martlesham, Suffolk. Since leaving BT I have undertaken consultancy work, and some contracted hardware and software development. Three years ago I decided to stop work and get back into education. After an abortive year studying Forensic Science I am now undertaking a BEng in Motorcycle Engineering at Derby University. And yes, I have extensive knowledge and experience in electricals and electronics, although I wouldn't presume to claim it is comparable with yours.



About that quote - I only speculated on one thing: is the BB product designed for wasted-spark systems or twin-spark systems? I demonstrated that the requirements were different and thus it is reasonable to ask the question. I also maintain that only BB will know the answer. Finally, I openly conceded that a wasted-spark system may well work perfectly well on a twin-spark system, because most ignition systems seem to have plenty of headroom in terms of the peak voltage capability.



I think that was, and is, an absolutely reasonable position to take and I don't believe anyone can find fault in it until more data is available. Please, I invite you: find fault in it.



Sadly, you next seem to accuse me of being a liar:



Also stated in the same post, Quote "For what it's worth, at college we measured the spark voltage on a Honda CB500 at idle, and it was a shade over 6kV, so I guess we're in the right ballpark." Now down to post eight you post a nice graph and state, QUOTE "I took this trace from a Honda CB500R last week.", What a strange coincidence.



Coincidence? Of course! I'm referring to the same event, although I admit to making a mistake - it was the week before last (Friday 5th December) that we ran the engine for the first time after stripping and rebuilding it. The captured traces were taken by our lecturer and are from an automotive PicoScope. As well as measuring the voltage traces, we also measured the primary current trace and the signal from the crank sensor.



Tediously, I've just been taught Kirchoff's Laws yet again - probably the fourth or fifth time by now - as part of my course. Please don't suggest I'm a liar again - I believe you owe me an apology.



I did have a genuine belly-laugh at this, though:



Sorry wrong. Kirchoff's voltage law is as follows..... (snip) the sum of the emfs in any closed loop is equivalent to the sum of the potential drops in that loop (snip)



You do realise that this is functionally IDENTICAL to my statement? "The voltages developed across the individual components add up to the voltage applied to the circuit as a whole."



I worked as an electronics engineer all my working life so please don't think you can baffle me with figures and laws and graphs you probably pulled off the internet.



Oh come on! I'm not interested in "baffling" you or anybody! I stated all my sources and invited challenges to my arguments. That's the way to do it. Instead of ad hominem attacks, you'd be far better supporting your own assertions with argument and evidence.



You went from a person speculating what may or may not be to a guru af all thing spark related in just seven days that is really some acheivment.



On the contrary, I've been such a guru for decades!!

[Norm]

People
Tim Busby Today at 8:21 AM
To
me
Hi Norm
I seem to upset Thack? (And wound up another?)
Can you post this for me on H forum?
I have attempted three times now to post a simple reply to explain why a misfire exist and how to fault find it easy peasy, but no posts have shown up on H list.
???

(I will retry to rewrite it as best as possible as first ‘posted)
As follows:

It seems I may have created a bit of a ruffle. No offence intended, may be I should have said ‘misguided’?

A double end coil fires two sparks, one Positive the other Negative. One spark wears the tip; the other erodes the earth strap. The two sparks travel through the coil in what is effectively opposite directions. The wasted spark (low pressure) requires less voltage to ‘jump’ its gap, than the ‘firing’ plug. If it didn’t the design would fail to function. Total system voltage remains constant with one plug (the wasted) requiring less voltage to spark
Misfire on one plug, or shorted and total ignition advance is affected and power is reduced: retarded = over heating + preignition/running on; replace BOTH plugs.
Total system voltage remains the same, and the coils are designed as such.

But that is not what the initial question was about. The crux of the matter here was about a misfire.
Q What is the first symptom of running out of petrol? The motor starts to misfire, back off the throttle and the engine will continue to run ok for a wee while until the fuel eventually is all used up.
Q: What is the simplest way to test to initiate a High speed misfire? Turn your petrol tap half closed.

Modern engines with hi-energy ignition systems, hi-compression and fuel injection are capable of running with far leaner (+15-1) air fuel mixtures than the humble carbureted Bullet. But no mater how intense the spark no motor is going to run if there are insufficient fuel molecules present to initiate combustion, let alone sustain it.
Even the common old Bullet coils is often times able to run a plug gap as large as 0.035” and well over 12,000 sparks per minute But bump up compression, have dirty pitted points or an oxidized connection in the circuit and the potential onset point of a misfire is reduced.

Misfire fault finding 101: Inspect plug for any sign of over heating, if so replace (colder) and reduce the plug gap.
Owners of mag bike should know that the first thing to do with a misfire is to close up the plug gap (0.15-0.18”)
If the problem eventually reoccurs, particularly once the motor is hot, it is usually a good indication the condenser is dying.
Points pitting? Replace the condenser.

Closing the plug gap is the simplest and easiest first step in misfire fault finding.

Working on a newly built and crisply tuned engine?
(Which with the Bullet typically is not that highly tuned even at the best of times!)
It is always better to start too rich than not rich enough. Note I do not say ‘lean’ The terms ‘Lean & Rich are relative and most home tuners fail to comprehend the significance.

Misfire onset @4000rpm? Closing plug gap (why oh why even think about replacing the ignition system!!!) fails to resolve or improve matters?
Fit a larger main jet! At least 2 size up.
(If the misfire onset was, for example, @3000rpm look to the needle jet…)

Roll on - Roll off throttle test.:
Engine at operating temp, riding up an incline/hill so that the engine is under load, in 3rd gear, full throttle, +4500rpm and the engine still accelerating.
(Big grin) J
Momentarily roll-back the throttle ¼” If the engine momentarily picks up revs and surges ahead the main jet it still too small.
IF the engine momentarily bogs and hesitates for an instance the main jet is too large. Snap the throttle back to full again; instant momentary misfire, go up another 2 jets
Plug chop. 99% of home mechanics do not have the faintest idea what they are really looking for, or at when they look at a spark plug!
But with a NEW spark plug (never do a plug chop on an old plug unless you TRULY know the motor!) the plug will look pretty much like it did when it came out of the packet! Clean, no blisters or bubbles on the surface, NO coloration, just a faint hint of BLACK soot creeping up the central insulation, and whiff of soot on the shell.
Heat band on the earth strap with a clear and well defined mid-point, no frazzling of the electrode tip.
And with twin plugs, the plugs SHOULD look cleaner (lean?) than they do with a single plug! Twin plug combustion IS better and more complete. The Mixture that previously ‘looked’ right with a single plug will now indicate ‘lean’. Its most probably isn’t, but there is no harm in running a larger jet.
Depends on Relative Air Density and the notes you keep…

Tim

[ChrisD]

Gentlemen thanks for engaging to answer my query. And thanks to DennisC for remembering me!

I have to admit to some confusion so far regarding the answer - just a tad you understand! Most of this electrickery is far beyond my mind (despite A-level physics and a series of degrees to doctorate) so you’ll notice I haven’t joined in.

Since I am busy trying out different cam and pinion settings, hoping to avoid the reversion (misfire at high revs where the fuel-air mix is pushed backwards out of the carburettor - very flammable just under my bum), I haven’t got to the point of worrying too much about a the ignition system (couldn’t afford it anyway). So you won’t mind if I avoid all the issues, “heated argu----- differences of opinion and just focus on a few days of glorious sunshine (Cape Town), too much wine, women, song and food and riding my perpetually reliable (but oh-so-boring) BMW!

May I wish you all a very Merry Christmas and a great start to the New Year when, insh'allah, my Bullet will ride again.
ChrisD