Ignition systems

Hi all, since there has been a lot of talk about ignition systems, magnetos and stuff lately, i thought this thread could be a good idea?
If not, please tell me.
I got the idea when i started restoring a small coil, and thought: hey, maybe i should share this?
To not invade Giorgio’s thread i started this, and this is for everyone to post, tips and tricks.
What do you think? Ignition systems are important to keep our engines alive, both old and new.
And ofcourse, also post ways to tamper with timing on various woodgas worthy vehicles :smiley:


And this is what gave me the idea of this topic, i tinkered some with my old Warsop petrol rock drill, it wont start, just puff, one or two times, the spark is strong and blue, and it could create a spark in a 1/4" gap, which would be enough to spark under compression pressure.
But, when it fires and rev’s increase the spark is gone, and it dies, why?

Well, i pulled the coil, small flywheel magneto system, but this works on other systems to.
Just to start cutting in this old “mummy”

This coil showed all good on resistance metering.

On this pic it’s visible a white, soft “mush” this is where the end of the thin, high tension wire is grounded in the thicker, low tension wire. This is probably where it shorts when voltage increases.

When down to the thicker wire, we should count every turn we roll of. 153 turns on this coil.

This is the core, we should tidy it up, and re-use it.

This is the thin, high tension wire, cut away, this is actually thinner than a hair. No idea to try rewind this without a machine. It’s up to 15000 turns! ( i dream about building a machine for this some day, oh or i started a build but…)

When cutting the layers of thin wire, please be careful not to cut deep in to your fingers :roll_eyes:


And the next part, the old coil is going to be a feeding coil for a separate high tension coil, mounted outside the flywheel, which gives it room for more cooling, and better insulation.
The old coil is going to get new, heavier gauge wire, in this case i use 0,75 mm enameled copper wire (you do the gauge translation)
The old had 153 turns, i put on about 200 turns for more juice.

Good tight turns, no gap between turns. Thin cardboard insulation next to core, so the core not chafing the wire.
Between every layer of wire is a layer of painters tape so wire not rubs. Not electrical insulation tap, it’s too soft.

203 turns, the ends is leaving the coil through each “spool gable” in many cases the end of the first turn is grounded/soldered to the core.
Next step is coming, the coil is going to get some cover on the outer layer, and wired to the new high tension coil.


göran, this thread is very interesting and usefull, thank you very much…i had loved it also on the historic tractor thread, no problem…
my son found a very thin copper wire, thin like a hair in the alarm clock from kitchen stoves, maybee can be reused…
have you bought the wire new?
have you a idea what they costs?


Yes good idea to make up this thread for future references and for right now discussions.
@Chris might be able to move the other parts into this thread to keep everything that has been talked about here. Very informative information.


Yeah. Good stand alone topic Goran.

On the, " . . . revs increase and spark gone . . ." the most common problem I have seen is a physically cracked flywheel. It RPM stretches gapping, then interrupting/weakening the PM magnetic field.

I read you now. I am not understanding the outside remote high tension coil??
So you change the under flywheel coil to just be an impulse charging source for that external coils primary?
Steve Unruh


Goran, this is a great topic, I also like your method of rebuilding the ignition coil, because the external high-voltage coil is much more robustly made and therefore more durable. On my Tomos APN 6 moped, this is exactly what is done, the internal coil produces an alternating voltage of approx. 24V, these waves are used by the external ignition coil, it already has a built-in transistor ignition system without a capacitor.


Hi Giorgio and thanks, i just thought it was good idea to collect all about ignition systems in a dedicated thread, no idea i mix in this in the tractor thread.
As for the wire, as i mentioned the high tension winding is troublesome to make at home, imagine up to 15000 turns, just to remember the number when somebody shows up and disturbs you, also, this thin wire cant be spliced, or the enamel cracked, then potential short circuit, hard to inspect a re-used wire that thin, also no “kink’s” (translation?) allowed, it would mess up the whole winding procedure.
The thicker wire thought, can be straightened, and re-used.

Enameled copper wire are available on the web, or companies that re-wind and repair electric motors.
This pic’s shows some of the wire i bought from electronics supplies on the web. Cost is very varying, due to metal prices, this wire is often priced after weight.
The small spool cost me 7,50€ and the bigger 7€. I bought them on different times.


Thank you SteveU, yes cracked flywheel magnets can be very hard to “diagnose”. About the same thing here, resistance good, good visible spark, everything good until voltage raises.
This is what im going to do in this case.

From this

To this. Coil outside of flywheel.
Almost the same a Tone describes, only im keeping points and condenser.


I apologize for writing above that the ignition is capacitorless, I actually don’t know what is hidden under the housing of this coil, but it produces a good spark for ignition. This system does not have a platinum switch to trigger the ignition timing, the ignition occurs when the magnets induce a voltage of a certain value in the primary coil, so the ignition timing also varies slightly depending on the engine speed.
Obviously, there are many different versions of “electronic” ignition, and as I said before, due to the switching speed, they enable very strong voltage induction, and also the high-voltage coil can be smaller and with fewer windings.


I’ve seen coils with built in electronics before, but never this type to mount outside the flywheel, very interesting :+1:
Going to look this up further, does it work with a homemade feeding coil?


i have found a video about coil winding some weeks ago…
he uses a “counter” for the windings…
my son has found also such a counter years ago when scrap exploring.
20 years ago i winded a coil for a relais for the regulator for wind energy…
i have winded it with the pedal turner, works well with this wire on the foto
but i think with the hair fine wire a hand driven tool for winding would be better for not tear the fine wire…
some month ago steve unruh posted somewhere a very instructive video about ignition damages, how and why they can appear…
this video would fit also here in this thread very well, i think
maybee steve can find it again?


Georgio I try to think back . . .
This maybe . . .

One of 16 on this man channel explaining modern, no-points: small engine ignitions systems.
How they work. How they fail. How to diagnose.
Watch on Youtube and open up his channel link on YouTube. Open up Playlists to find these 16.

Modern no-mechanical trigger points systems use a small second flywheel mounted magnet just as the transistor timing triggering impulse. The main magnets still used to help generate the energy for the the H.T. spark making.


Ha! For me his 16 videos seems to auto feed if I let it.


yes, exact this video, thank you steve…
since i have seen it, i slept not so good more…what can happen to my ignition coils…
have ordered some spare pieces for every case …


Goran, there are external coils with several wires for connection, where a kind of spark trigger is connected, well, on the Tomos moped, you can see a coil with one wire, which is connected to the internal coil, which provides alternating voltage (nominal voltage 12V) and ground wire. I don’t know exactly how it works, but I assume that the spark is triggered at a certain voltage, namely the voltage wave increases and charges the CDI unit, and when it rises to a certain value, the gate of the transistor opens, which allows the capacitor to discharge quickly through the coil…

9781637760727_Ch10.pdf (2,4 MB)


A very interesting subject to me. I think engines burning woodgas but sometimes gasoline would really benefit from a knock sensor, self timing adjusting ignition system as found in OBDII systems. It is my understanding that Atom Industries of Australia started doing this for small engines back in the 1970s. @k_vanlooken pointed me to this video a while ago.


Very good comprehensive article on CDI Tone.
Next to last to the end in “^ Similar Non-CDI systems” is described an Energy transfer system I asked Goren if he was trying to set up with the external coil being energy supplied by his converted hand wound.

And the last section “^ Advantages and disadvantages of CDI” is described how it can be used, " . . . with CDI . . . The current flow over the spark plug can be then be used to calculate the temperature and pressure inside the cylinder."
GM was the first to do this for their electronic EGR controlling. I’d wonder how. Now I know.

As described CDI has normally a very short duration spark.
Bad for woodgas?? I think the woodgas fuel gases do not spark gap ionize as redibly as gasoline components. Needing a longer duration spark to more reliably ignite.


Yes, there are alot of various systems available, the cdi’s and others i know about.
This coils with built in electronics is a further development of the points substitute chip (invented by Atom industries that Rindert mentions)
Often based on a simple circuit with a thyristor if i remember correctly? When the voltage reaches it’s peak, and drops, the thyristor trips and breaks the circuit.
Good stuff, what made me interested in the coil you showed is i never seen one “universal” type that mounts outside the flywheel, other types that replaces original coil, points and condenser has become very popular, and cheap, only trouble for me is they don’t fit all flywheel magnetos, therefore an external coil would be very useful for some projects (chainsaws) :smiley:


Goran, I think that the outer coil with the “classic” platinum switch that ignites the ignition allows a stronger spark, the first thing is that you can wind more turns on the inner winding, which means a higher voltage on the primary winding, and the second difference is in the rapid decline of the magnetic field in the core of the outer coil, which does not “disrupt” the magnetization of the permanent magnets. Permanent magnets prevent the complete annihilation of the magnetic field in the internal coil, so the change in the strength of the magnetic field is not so pronounced and the voltage induction is less.