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I've got a 2 stroke 1 cylinder engine and its ignition system doesn't seem to work. I'm having problems with my magneto ignition system and I need help connecting everything up. I think I've connected everything right, but it still doesn't work. Am I missing another part like another coil? Should i replace it all or could you guide me how to fix it?

Edit (a little more info): It's an old soviet engine from a moped. I got it from my grandpa and i have never seen it work. I have tested the spark plug in a different engine, it works. I have tested for the spark (taking out the spark plug, touching the thread to the heatsink and trying to start it) it does not work. I have tried connecting a multimeter to the coil and i've gotten 1-3VAC. The carburator works flawlessly, the only problem i found was the spark.

Edit 2: I have tried to mostly rewire it all, I have replaced the capacitors to 2x 0.5uF capacitors wired in series. Tried to crank the engine and no dice, didn't produce a spark. The HV coil(the one that connects to the spark plug) when measuring to ground has a huge resistance of ~5mOhm while the other coil (LV i think, but not sure, the one that connects to the switch) has ~0.5Ohm. Are the coils wired up the wrong way or are they dead? (Sorry for a little sloppy soldering job in the new picture)

The coil and capacitors Rewired system **Magneto ignition system**

enter image description hereenter image description here

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  • Welcome to Motor Vehicle Maintenance & Repair!
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    May 20, 2019 at 20:22
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    May 20, 2019 at 22:10
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5 Answers 5

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The main issue with the ignition was that i was missing another High Voltage coil, but before knowing that i had replaced the capacitor, bolts, sanded everything clean, so the connections would be good. As of now, the ignition works, but my timing is a little off and I'm having a few problems with my carburator so, it hasn't been started yet. (I still have problems starting it so that's why I took so long to write this answer) Some pictures to show the Ignition system as a whole: [Main System[1] The HV Coil Sparkplug with its wire The Schematic

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  • If you ever have the time/inclination, I'd be very interested if you could show a schematic with the new coil. I'm having trouble following the wires in these pix, but it seems like maybe there are some changes from the original drawing? Thanks.
    – George
    Jun 8, 2019 at 2:34
  • One thing - it looks like the two replacement caps are wired in series. If so, and in case you don't know, putting caps in series reduces the net capacitance by 1/2.
    – George
    Jun 8, 2019 at 2:36
  • I totally forgot about the schematic, I'll draw it and add it. I couldn't find the appropriate ~250nF cap, so i bought 2x 500nF.
    – PotatoMan
    Jun 8, 2019 at 7:11
  • @George I have no idea about the coil windings, but the schematic looks about right now and I've also added an on/off switch.
    – PotatoMan
    Jun 8, 2019 at 10:21
  • Thanks. I think it probably is an 'energy transfer' ignition, though I remain puzzled as to what benefit that provides. But that's my problem. I may post about it in some other forum. If I do, would it be OK if I use your pix?
    – George
    Jun 9, 2019 at 15:37
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(More an extended comment than an answer, but whatever ...)

  1. If you haven't done so, I would check the points. Typical gaps are 0.020" (0,5 mm?)
  2. I have trouble seeing spark when turning the engine by hand. So, I do it in a dark place, and (if possible) crank the engine with a drill.
  3. Re whether you need an additional coil: there are ignition systems that do, called 'Energy transfer ignition'. This article, has some description of these, and says

Energy transfer is found on most vintage offroad bikes, scooters and ATVs

All I can say is 'maybe'. I don't know anything about them; and, just looking at your picture, I don't see where the additional coil would fit. But, I'm coming from profound ignorance.

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  • I have checked the gap, it looks good, i am cranking the engine currently with a drill (because i don't have a pull start or anything like that). I will try out changing some wires and a capacitor today, crank the engine in a dark place and check for the spark. Thank you for the answer!
    – PotatoMan
    May 22, 2019 at 4:53
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I wrote a giant answer just to realize that I was putting my foot in my mouth.

What you have there is a magneto points and breaker ignition. I can't tell where the sparkplug connects but if I had to guess it is to the wire from the coil to the left bottom stud in the picture. Please let me know if I'm wrong.

Your connections (with the above assumptions) are correct. The top left stud is then used to shut the moped off by grounding it. Leave it unconnected externally to run.

Make sure that the points are clean and not burned. Also check, double check and, triple check the capacitor. That is going to be the week link in the system. If the capacitor is bad it will keep the system from sparking.

enter image description here

This is what I would expect the wiring to look like. Please note the "expect" part. This is what a typical points ignition would look like normally.

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  • Yes, the spark plug should connect at the bottom left. I have checked the capacitor and it looks like its capacitance is ~220nF (i have no clue if it's still good or not, so i might buy a new one). Thank you for the clarification of the "shut down" stud and does the system look complete or am i missing another part? I have seen similar systems which have another coil.
    – PotatoMan
    May 21, 2019 at 14:29
  • @PotatoMan To the best of what I can see from the picture it looks complete. The coils should have a connection to the chassis somewhere. This may be internal.
    – vini_i
    May 21, 2019 at 19:10
  • Yes, it has a connection to chassis. Good to hear that's its complete. I'll try to change the capacitor tomorrow, change some wires, clean everything up and see if it helps, thank you.
    – PotatoMan
    May 21, 2019 at 19:14
  • I have tried changing the capacitor, but it didn't help.
    – PotatoMan
    May 22, 2019 at 14:47
  • @PotatoMan check the points. Do they open and close cleanly? What is the contact resistance? Are they in time (do the points open on or just after TDC)? If all of that checks out it might be the coil, that's where things get difficult.
    – vini_i
    May 22, 2019 at 15:13
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I have taken it out of the cage right now and i see the skinny wire coil connect in series to another skinny wire coil through 2 what it looks like capacitors and that coil has ~5kOhm resistance to ground. I will attach a photo to the question shortly

this was meant to be a comment, but i pressed answer by accident

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(extended comment, really - elaborating/questioning my own last comment on your answer, WRT being 'an old auto ignition')

  1. Configuring as such would require a significant change to the wiring you now have. (cf "wiring diagram", with the output of your diodes replacing the battery.) In particular, the 'ground' terminal of the HV coil would be wired to the points, replacing the wire from the 'first' coil. So, if you trust that the present wiring is as it came originally, this idea seems like wishful thinking on my part.
  2. If the wiring history is uncertain - so the HV coil 'ground' might properly be wired to the points - then what is to be done with the resulting disconnected end of the 'first' coil? All I see is to ground it. Is there any provision for that? And, the behavior of the 'second' coil in that case is unclear to me. There should be current in the (shorted) first coil, but it's not clear that any voltage would be induced in the second. If not, no generator.
  3. As shown in the above-referenced link, the HV coil would need 2 terminals in addition to the HV cable - namely 'battery' (connect to the diodes in your case), and 'ground'. Is the HV 'ground' connection (as show in your schematic) brought out on a wire?
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  • Firstly sorry for taking so long to respond, but i think the wiring is correct, it shouldn't need a battery or anything like that, I am getting a spark(sometimes misfires, but a spark nonetheless). The ground on the HV coil is just it's case/core.
    – PotatoMan
    Jun 17, 2019 at 15:24
  • It sounds like this question is resolved, then? (The answer being that the additional coil was required, as you discovered.) If misfire is now the problem, you might want to start a new thread - this one has gotten pretty tangled. (Largely my doing, but that can't be helped now.)
    – George
    Jun 19, 2019 at 12:25

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