spark plugs

[Morala]

I have a 1974 cb550k which has a boyer ignition fitted, i was led to believe that the ignition fired all 4 plugs at the same time if this is the case the silly question is does it matter what plug leads go to a particular plug regarding firing order thanks for any advice.

[McCabe-Thiele (Ted)]

Yes it does as each pair of coils have to be connected in the correct firing order as dictated by the camshaft that is running at half crank speed.
It does not fire all four plugs at the same time, for a given coil there is a wasted spark, i.e. it sparks on compression on cylinder1, it also sparks  on cylinder 3 that is on the exhuast stroke (wasted spark). Similarly the other coil sparks when cylinder 2 is on compression. the wasted spark is on cylinder 4 on the exhuast stroke. This repeats itself on the next cylinder rotation to fire on 3 & 4.

Two sets of points control the two coils from the lobe at the end of the crank, the Boyer system emulates the points, if it fired all four at the same time you would be igniting fuel on the induction stroke as well as firng a cylinder on compression.

[K2-K6]

The Boyer (later iteration) do fire all four plugs simultaneously and noted in their instructions.

It "shouldn't" matter in which way they are connected from this as asked by OP. I’ve not set one up in contrary fashion, so no direct experience of doing it wrong, as it were.

They don't disclose if there's parallel switching hardware, then to trigger both discreet output for the two coil OR if there's one switch set, triggered by both trigger set. I'd have thought the first would give redundancy to switching and logic, with the second giving some half redundancy to trigger hardware.

My inclination and experience to set them conventionally (1&4 / 2&3) coils to plug arrangement, and conventional to most bike like this, is more to save confusion in diagnostics etc, even if it was not me looking to fault find. But if there's good reason to go against that, it would be simply a test of function in verification. 
Its also unconventional in tbat it has no advance, just static at full "advance" mechanical position, then to retard within onboard electronics based on rpm trigger read to give low speed notional timing, this effectively set back from that static setting. That too leading to the final setup instructions of checking the timing dynamically and above tbe rpm at which the "advance" attribute plays out. Technically that's good, as full advance is more critical in cylinder performance and safety aspect.

It seems a quirky system, but really with very good logic, just appears different when judged against the conventional.

[McCabe-Thiele (Ted)]

So the Boyer ignition is firing not just on a cylinder compression, it also fires part way through the induction cycle. Would that not cause premature burning in a cylinder part way through the induction cycle of a four stroke engine, with the inlet valve open that would create a risk of fuel burning back into the carburettor. That sounds like serious built in pre- ignition.

An extra spark on the exhaust cycle, I can accept that as it's not burning fresh fuel.

[Sesman]

Hi, Ted. I’m not an authority on the topic, but I’d imagine that without a complete induction cycle including compression there would be no risk of premature ignition. The spark is as they say…wasted.

[Johnwebley]

I have used Boyer since the late 70s,

Set up on full advance

I have always fitted the leads as 1-4,2-3,but it does run at any fitting



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[Morala]

thanks for all your input guys

[McCabe-Thiele (Ted)]

Hi, Ted. I’m not an authority on the topic, but I’d imagine that without a complete induction cycle including compression there would be no risk of premature ignition. The spark is as they say…wasted.

I would expect petrol vapour to ignite if there is a spark firing whilst the piston is sucking in air through the inlet valve once the engine is hot, especially as the spark fires before TDC anyway.

Could it be that the inlet valve timing plus the spark advance mean the wasted spark fires just before induction actually starts. It's a difficult process to visualize, but if members say their Boyer system is immune to firing order then I have to accept that's the case.

On the positve side the plug leads going from the left coil to 1 & 2 will look much tidier as it is not having to cross over the middle of the frame.

Another thought, does that mean it will wear out the coils twice as quick as each coil sparks twice as often as a points based system ?. As the Boyer also does without the mechanical advancer it must be a clever box of tricks that also acts as it's own crank position sensor.

[Sesman]

But it doesn’t does it Ted!

[Sesman]

Regarding wear and tear, I’d imagine that the LT side is subject to magnetic forces stress and the HT side subject to insulation stress. Though I’d guess it’s all relative and both coils will experience magnetic and insulation stress to some degree. I’m basing this notion on basic power transformer theory.

So yes, if the units spark twice as much I’d expect increasing wear and tear…though whether this is detrimental to longevity is anybody’s guess.

[Sesman]

On the original question, yes the HT leads do need to go on the correct plugs or you could be 180 degrees out on firing order.

[K2-K6]

On the original question, yes the HT leads do need to go on the correct plugs or you could be 180 degrees out on firing order.

It doesn't need that either.

Most fours being a "flat plane" crank arrangement, this with triggered input at crank speed, still not affected.

Every time any piston is at TDC (power stroke) there'll be a spark ready and waiting.  It's effectively firing ALL plugs at every HALF crank revolution.  That's from being installed with the two crank sensors at 180 degree to each other.

That'll catch every firing order combination wherever the leads go to.

[K2-K6]

So the Boyer ignition is firing not just on a cylinder compression, it also fires part way through the induction cycle. Would that not cause premature burning in a cylinder part way through the induction cycle of a four stroke engine, with the inlet valve open that would create a risk of fuel burning back into the carburettor. That sounds like serious built in pre- ignition.

An extra spark on the exhaust cycle, I can accept that as it's not burning fresh fuel.

It's the variance in conditions (compression etc ) that stops the wrong thing happening in the wrong place.

Even with a low compression (estimate, much below about 90psi) then a closed and compressed cylinder will have trouble igniting the predetermined mixture at expected ratio of fuel to air.  Little or literally no risk seems realistic in this "Boyer" scenario.

Pre ignition does agree with this when seen. IF there was hot glowing heat source (think old coked combustion chamber) then that too will only fire at pre ignition point as compression comes up to squeeze the volume and subsequently be set off prior to spark arrival by that combination of glow & compression at reasonable level being presented to the whole ensemble 

A friend's uncle had a really coked up (different meaning nowadays  in the Henry Cole idiom ) Triumph Spitfire which would, on a visit to their house, have uncle dipping a rich tea biscuit into his first mug of steaming  tea before the car stopped chuntering away in the drive, after being switched off on arrival 

Also a risk in running engine on a dyno at extended load, if low number (in NGK terms) plug was inadvertently let to go over temperature, then glowing earth or tip can cause pre ignition, with subsequent piston melt experience 

[K2-K6]

 " As the Boyer also does without the mechanical advancer it must be a clever box of tricks that also acts as it's own crank position sensor. "

Yes, that's correct Ted. The fixed final positioning has absolute and direct relationship with crank rotation, and no mechanical displacement at all when running.

Hence the need to accurately set it AFTER any internal timing has played out (rpm lifted above any internal set point to check) from the "retard" method within the electronic scheme in play.

The firing event would be in the following order:- timing point arrival (at maximum set advance) then added delay to that signal based on rpm scale below the maximum advance positioning.  This to give the designated start and tick over timing, then to move up that internal scale by monitoring the absolute rpm, to arrive at the "no interference" final mechanical position providing the desired ignition advance. This should be completely native and reliable to produce that figure for the most demanding load conditions.
It can also, does, also multi fire the plug under certain conditions to give best chance of combustion, from memory at very low rpm /start speed, in order to facilitate starting that may have sub optimal mixture present.

[deltarider]

Before chosing, I would need a complete picture, so I'd like to know:
what the effective duty cycle (dwell) is,
how much amps that B&B kit draws with the engine running (OEM coils), both at idle and revved and
if more erosion at the sparkplug's electrodes is to be expected.
Is that info public? By B&B?