[Greg737]

I finally ordered a copy of the Service Manual and the Service Manual Supplement. Now that I've read through it I've come to realize the Ignition system on this bike is a pretty simple-minded thing. But the manuals don't go into much detail about the ignition system so I want to ask a couple of questions.

(The near complete absense of Ignition System information in the FAQs speaks to the fact that there's just not much going on in it and also that it's a pretty reliable system. And that there's almost nothing that we as owners can (or need to) adjust or tinker with in it.)

From the Service Manual Supplement drawing and description I'm wondering if the EX-250 engine is a "wasted spark" system, which means that the spark plugs fire every 360 degrees of engine rotation regardless of whether that particular cylinder is in it's compression stroke or not?

Greg

[loudboys]

The engines than use a wasted spark system are those with direct ignition, and mulitple cylinders (usually 2) plumbed to each coil.

Those are pretty unusual, but I seem to remember GM doing something like that back in the '80s-90s.

[Bokonon]

[dizeldawg]

[Greg737]

Looking at the Service Manual Supplement drawings I see just one Pickup Coil and just two wires leading from it to the IC Igniter box.

Based on the drawings, I can easily picture in my mind a simple system (wasted spark) that triggers both ignition coils each 360 degrees of crankshaft travel (every time the crankshaft sensor passes the Pickup Coil).

But I can't figure out a more complex system that would somehow know where it is at any given moment in the normal 720 degree four-stroke engine cycle.

So, because I'm not well versed in ignition systems so I have to ask "How do it know?"

[Industrialfish]

[geekonabike]

the CB250 is a 360-degree parallel twin, so they went with a single carb and both plugs firing at the same time.


<uninformed>
The EX250 revs so fast I think it would be more "wasteful" than the slower CB250, and of course if they went with a single coil on the EX250 it could be disastrous because of the 180-degree crank difference, as you'd get a spark during the late intake of the lagging cylinder (and late compression stroke of the leading one). It might not ignite in the low pressure of the intake, but then again it might. I don't think what could happen then would be just called a "ping." The EX250, I'd think, would go through plugs a lot faster with a wasted spark, but maybe not so much, and it may have some benefits. It seems Kawa didn't go with it.
</uninformed>

--Mike D.

[Leon]

The trigger for the spark is on the crank, not the cam.
Since the signal is coming from the crank position, the system has no way to identify whether the cam is at the top of compression or between exhaust and intake. Therefore in order to start, the ignition would have to fire every time around rather than every other time around.

[loudboys]

which makes me wonder why they set it up that way.

You could easily set it up to run on one larger coil, and free up the space on one side of the engine for other things.

[nts472]

i have a service tachometer that clips on the spark plug cable like a timing light...if its a wasted spark system it'll show double the rpm of the bike tach.

[dizeldawg]

[loudboys]

[Bill Hoddinott VA]

Exactly. The rotor is triggering sparks for each cylinder at the right time, but the sparks can only light up something on the compression stroke. On the other stroke the valves are open and there is no compression so the sparks occur but no combustion.

This system has the virtue of great simplicity and reliability. I've never touched any part of the ignition or charging system in my '88 in 129K miles except spark plugs and batteries when worn out.

I had occasion to replace the stator cover in one of my spare engines and I was impressed by the STRONG magnetism of the rotor. It sucks the stator into itself very hard when you begin to put the cover in place. That magnetism and the coils of the stator put out lots of electrical power.

More good Kawasaki design. I was up at one of our local Kaw dealers the other day for a few bits and pieces and a new 2009 250 Ninja was in the lineup on the showroom floor. The blowhard salesman said, "Yah, I could sell 20 of those a month if only I could get 'em!" Glad to hear it. At the other end of the system, I noticed a very low mileage 2008 engine being offered by one of the FL junkyards on eBay recently for $999 "or offer". Or offer means he would probably take $500 to $750 and it's a lot of value for the money. Too bad the engine mounts don't match the 2007 back.

[nts472]

[dizeldawg]

According to the parts diagrams at Bike Bandit, some newer BMW's and Triumph"s have coil-on-plug.

[dizeldawg]

I understood the post exactly. The coil won't fire with out a pulse from the ignitor box. Each coil has it's own pulse wire. The tach only uses one of the two pulse wires. Therefore, the coil will fire at the same time the pulse wire signals the coil. His clamp-on service tach will read the same as the tach if it's connected to only one spark plug wire.

[nts472]

if its a wasted spark system then:
both coils are fired at the same time, one cylinder will be in the combustion position while the other in the exhausting position... in this situation both coil trigger lines will fire at the same time... hence 2 sparks per 4-stroke cycle or 2x rpm if measured at the plug

if its a true independent ignition systems then:
for each cylinder there is 1 spark at the combustion stage, which would yield 1x rpm measure at any plug

after looking at the wiring diagram i am almost certain that its an independent system, for the fact stated above, that the tachometer takes off directly from out 12v pulse of the coil ignitor for 1 plug only

HOWEVER it can be a wasted spark system if it turns out the tachometer somehow mechanically halfs the pulsed rpm, in which case the clip on tachometer will show 2x the bike tachometer.. i find this unlikely because of the design overhead on the bike that would imply an independent system..but I'll see tomorrow

[Dailyrider]

[nts472]

i wouldn't be surprised if you have a DSC button on that thing

[Greg737]

My bet on the outcome of your tests is "wasted spark" based on the drawings and what Bill and Leon had to say.

The one confusing item in the mix is the presence of two coils. You never know what a motorcycle or car company will do when sourcing things out of their "parts bin." Two coils in a wasted spark two cylinder engine might have made some strange sort of sense at the time.

Anyway, we're all waiting for the test outcome.

Greg

[nts472]

Independent spark!!!!!! ...lol well i think... for some reason my tachometer wasn't giving reliable results, the rpm was all over the place.. its been tossed away so it might be broken.. so i grabbed my timing light and set the bike idle as low as possible ~800rpm indicated and the flash rate seemed about that of an idling car from my experience..so i assume its a 1:1 measured to indicated tachometer ratio.

when i get a chance I'll hook up the coil trigger wire to my hand held o-scope and measure it directly to confirm this, but I'm pretty confident of the results.

the only thing that does confuse me is the ignition trigger... its plausible that there is an alternating trigger but how would it know which piston to fire?

[geekonabike]

Wouldn't you want two coils on a 180-degree twin? Otherwise I'd think there would be three wasted sparks per cylinder, some being perhaps highly destructive. Sparks every 360 degrees per cylinder seems reasonable to me.

I'm missing something?

--MD

[nts472]

i just did up this little diagram to make sense of this, pardon me if i'm completely wrong, i only slept 2hrs last night and I'm a bit punchy

pretty much...

BLUE - fresh charge just drawn in
RED - ignited charge
ORANGE - expanding gases (after ignition)
GREY - spent charge just exhausted
YELLOW - spark plug fire (i assumed independent coils)

for illustrative purposes i assumed TDC spark plug fires


if this is correct then a wasted spark would fire in a chamber full of uncompressed fuel/air at 540 degrees..can't be good...

again i could be complete wrong here, please correct me if i am

[nts472]

[Dailyrider]

In the 60's, when Honda made the Hawks and the Dreams, the Hawks used the 180 degree crank and the Dreams used the 360 crank. They both had waste spark, but the Hawk used 2 coils, while the Dreams used only 1 coil with 2 HT leads. Our little Ninjas use the waste spark also, and since they also use a 180 crank, they have 2 coils, just like the Hawks.

The early Triumphs were also 360 twins, but they never adopted the single coil with 2 HT leads, they always used 2 coils, but fired them at the same time every revolution. We used many, many Dream coils to replace the twin Lucas coils, because the Honda coils were much more reliable and took less space and wiring.

The Triumphs also used a taper for their points cam, in the end of the exhaust cam, if the taper didn't go in exactly square, you would end up with a spurious points opening, with the resultant spark and end up with a dime sized hole in a piston! This was a real problem for Triumph in '63, until the factory figured out what was happening. This is basically what would happen if you tried to use a single coil with a waste spark on a 180 crank engine.

[Greg737]

The total rotation for the full four stroke cycle is 720 degrees.

Your diagram needs to have a fifth frame that takes the left cylinder back up to the starting point in the first frame, or an arrow pointing back to the start with a note mentioning the remaining 180 degrees in the cycle.

Also, it seems that your current ordering of the stroke cycle has the two power pulses occurring only 180 degrees out from each other. Wouldn't that give the EX-250 a Harley Davidson sort of exhaust note?

[Leon]

[Greg737]

[nts472]

yeah i know its missing the last 180 but it seemed obvious, as for power pulses i don't think they can exist any other way with a 180 crank...i'm gonna create a new post to get more answers on this

check out the diagram three

[Greg737]

Beyond that, it's just a question of "what's the firing order" which should be addressed in the Service Manual (I don't have access to mine right now, I'm on the road tonight).

[B4theZ]

Emissions requlations probaly have a part in this. I haven't researched this, but some systems fire agin on exhaust to burn any residual fuel oil Etc if it will ignite. Yes, I know there is not enough pressure, but I saw this in a Nissan I used to have. The shop explained it to me while we were chatting one day.

Hey it is as good a theory as any other I've heard.

[dom]

[nts472]

i was thinking wasted in the way a v6 might be wasted spark fired...makes sense now... is wasted in terms of time, not cylinder

[nts472]

first off thanks to leon for explaining how exactly the ignition wastes a spark..this was the part i wasn't getting...

BLUE - fresh charge just drawn in
RED - ignited charge
ORANGE - expanding gases (after ignition)
GREY - spent charge just exhausted
YELLOW - spark plug fire

the grey circle is the crank..I and II are the piston TDC trigger (1,2 respectively) and the green thing is the pickup.. the exact mechanism of the pickup/trigger isn't important... its job is to simply fire the coil of the piston that is currently at TDC

the wasted spark here is that no matter whats stage the cylinder is in as long as its at TDC it fires..the cylinders are 180 apart so 2 coils are needed
the state of the engine at 360 and 540 would prevent the use of 1 coil firing both plugs

because it wastes the spark in terms of time and not in terms of cylinder the sparks fire at 1x rpm of the crank..which i did observe

[Leon]

That's nice. I wonder if Bokonon is watching. This ought to go in the FAQ (I haven't read it recently, so perhaps it or something similar is already there.)