Ignition testing

[rwh]

I'm thinking about how I could test whether my plugs are firing properly.

My thought is to wrap a turn or 2 round each plug lead, to pick up a signal when the current flows, and then hook it into an oscilloscope.

Since I don't have an actual oscilloscope (though I could probably borrow one), I was thinking of using the software that's available to provide an oscilloscope display from a soundcard microphone input. The frequency response should be fine; sound is much higher frequency than engine revs.

I'd obviously need some gadget in between, to make sure I don't accidentally try igniting my PC with the high voltage - or even just cook it slightly from not knowing what voltage my windings are going to give me.

Anybody done this kind of thing before?

Theories on how to approach it?

Thanks,

Richard

[doc]

I'm thinking about how I could test whether my plugs are firing properly.

My thought is to wrap a turn or 2 round each plug lead, to pick up a signal when the current flows, and then hook it into an oscilloscope.

Since I don't have an actual oscilloscope (though I could probably borrow one), I was thinking of using the software that's available to provide an oscilloscope display from a soundcard microphone input. The frequency response should be fine; sound is much higher frequency than engine revs.

I'd obviously need some gadget in between, to make sure I don't accidentally try igniting my PC with the high voltage - or even just cook it slightly from not knowing what voltage my windings are going to give me.

Anybody done this kind of thing before?

Theories on how to approach it?

Thanks,

Richard

If you ask the older more experienced bikers like Motu, Scumdog etc. They would explain how you just removed them from the cylinder head and had them touching on the edge of the head and when you turned the engine over they sparked. I however just got my kid brother to hold on to them while I cranked it over. He lives in Aussie now and I don't see him much .

[rwh]

If you ask the older more experienced bikers like Motu, Scumdog etc. They would explain how you just removed them from the cylinder head and had them touching on the edge of the head and when you turned the engine over they sparked. I however just got my kid brother to hold on to them while I cranked it over. He lives in Aussie now and I don't see him much .

Yes, I'm aware of that method. However, it's at idle speeds that it's running roughly, and it's kind of hard to leave it idling with the tank off, without some extra bits of fuel hose anyway. And I'm pretty sure they're firing most of the time, and watching by eye won't show me the occasional miss, where the PC digital scope software should be able to store it.

Richard

[doc]

Yes, I'm aware of that method. However, it's at idle speeds that it's running roughly, and it's kind of hard to leave it idling with the tank off, without some extra bits of fuel hose anyway. And I'm pretty sure they're firing most of the time, and watching by eye won't show me the occasional miss, where the PC digital scope software should be able to store it.

Richard

It's all beyond me too.

[xwhatsit]

Cool idea. Can you be assured, though, that if the plug receives a certain threshold of voltage it will spark? I suppose it will, if the plug's in good nick... I don't know.

They're hella high voltages they pump into spark plugs, so you will need to limit it somehow. I'm not a very capable man with analogue electronics, but I would've thought some kind of transformer and then a normal 7805-style voltage reg would get what you wanted, if you were going to plug it into your computer.

There's plenty of interface boards out there that connect via serial or parallel ports that would do the trick. Might require some minimal programming to get the correct representation of data. PC digital scope software... sounds interesting. Probably simpler that way.

I suppose your problem is is deciding what a misfire is. Is it an absence of a voltage altogether, where you'd expect a peak to be? Or is it a lower voltage peak than usual? Where do you draw the line at what is too low to be deemed a normal spark that ignites the mixture? Of course, since you are reducing the voltage to get into the right range for your 'scope, this will screw with this concept of `threshold', as any regulation of voltage you do will not necessarily be linear.

With my limited knowledge it would be a prick of a thing to do, but maybe there's a simpler way. At any rate, best of luck, sounds like a fascinating diagnostic method.

[howdamnhard]

I'm thinking about how I could test whether my plugs are firing properly.

My thought is to wrap a turn or 2 round each plug lead, to pick up a signal when the current flows, and then hook it into an oscilloscope.

Since I don't have an actual oscilloscope (though I could probably borrow one), I was thinking of using the software that's available to provide an oscilloscope display from a soundcard microphone input. The frequency response should be fine; sound is much higher frequency than engine revs.

I'd obviously need some gadget in between, to make sure I don't accidentally try igniting my PC with the high voltage - or even just cook it slightly from not knowing what voltage my windings are going to give me.

Anybody done this kind of thing before?

Theories on how to approach it?

Thanks,

Richard

I've got a strobe/rev counter for doing timing and it uses induction around the ignition leads to read the revs.Maybe you could get someting like that from supercheap or repco and adapt it to suit your needs,just a thought.Have you tried removing one lead at a time(if you have more than one cylinders),the one that makes no difference when removed is the culprit.

[Paul in NZ]

Why would you want to do this? Its a lot of bother to reinvent something you don't need when for bugger all you can just get a strobe light with an inductive clamp and you will soon see if its OK.

90% chance your carbs need synching if it's idling rough......

HOWEVER - if you are going to service it - do it properly by the book! Oil / filter / air filter / valves / ignition / carbs

[rwh]

Firstly, I got a bit of the theory wrong. I don't want to wrap my wires round the plug lead, I want to put a transformer core round the plug lead and wrap my wires round that. That way, current through the plug lead will induce a voltage in the test wire. Correct?

Cool idea. Can you be assured, though, that if the plug receives a certain threshold of voltage it will spark? I suppose it will, if the plug's in good nick... I don't know.

If I'm detecting current, then it's going somewhere - either arcing (sparking) or shorting.

I've got a strobe/rev counter for doing timing and it uses induction around the ignition leads to read the revs.Maybe you could get someting like that from supercheap or repco and adapt it to suit your needs,just a thought.

That could work, though perhaps a bit more dosh than I was intending to spend. Also, if it's like most test instruments I've seen, it would be hard to leave in there while sticking the bike back together to the point it will run (at least need the tank back on).

Have you tried removing one lead at a time(if you have more than one cylinders),the one that makes no difference when removed is the culprit.

True if one plug was consistently failing; the engine is running on all 4 most of the time. I want to know if the times it appears not to are due to lack of spark or something else.

Why would you want to do this? Its a lot of bother to reinvent something you don't need when for bugger all you can just get a strobe light with an inductive clamp and you will soon see if its OK.

You may well be right, but I'm not sure what the strobe light will tell me. I'm hoping to record a trace and see if it's regular.

90% chance your carbs need synching if it's idling rough......

HOWEVER - if you are going to service it - do it properly by the book! Oil / filter / air filter / valves / ignition / carbs

It's just come back from having all that done at the shop; they're a little mystified and I'm trying to both help sort it and learn something

If I can, I'd like to put these little transformers in on all 4 leads, leading out to a plug poking through the fairings or something - then I can plug in to any of them after I've been out for a ride ... or even during if I take my laptop ...

Richard

[Paul in NZ]

If I can, I'd like to put these little transformers in on all 4 leads, leading out to a plug poking through the fairings or something - then I can plug in to any of them after I've been out for a ride ... or even during if I take my laptop ...

Richard

I think you are more likely to stuff your laptop Richard. Its a pretty simple bike with limited places for things to go wrong so start with the real basics. IF a plug lead is shorting out or passing current to earth there will usually be some physical evidence of it OR you could try it at night where the arc might show up. Having said that a physical inspection of the leads is usually enough and while you are doing that give them a clean as dirt can cause problems.

If you post an full account of whats wrong and whats been done it might become more obvious and the clever KB folks could offer a better opinion?

[car]

My thought is to wrap a turn or 2 round each plug lead, to pick up a signal when the current flows, and then hook it into an oscilloscope.

You're talking about inductive timing sensors, yes? They're not new. The only ones I've seen have been at the other end of a traditional timing gun, and the sensor itself just clamps onto the HT leads. Handy for avoiding the HT shock that I always seem to give myself when messing with dynamic timing (no fun when your head's inside the rather cramped engine bay of a VW camper.) But I'll bet you that there's already a kit to do what you want to do. Or an article in some electronics hobbyists' publication on how to do it.

I had a quick Google, for fun, and found nothing combining inductive timing and PC oscilloscopes, but there are a bunch of hits for each separately. This one looked promising:

http://www.messaggeri.it/xmisuretest.htm#pcmeasuring

Good luck.

[rwh]

I had a quick Google, for fun, and found nothing combining inductive timing and PC oscilloscopes, but there are a bunch of hits for each separately. This one looked promising:

http://www.messaggeri.it/xmisuretest.htm#pcmeasuring

Good luck.

Cheers - bookmarked for later reference.

Thanks,

Richard

[bimotabob]

Hi

I would buy 2nd hand CDI and coils plus anything else obtainable for the bike.
Substitution although not exactly high tech solves problems and gets it going at the same time.
Since many 80's bikes have a history of bad electronics I have used this method for years. I try to have a full kit of parts for any bike I own as I can't afford to be off the road.

Buy another bike for spares - can't be worth much compared to new parts.

Cheers
BB