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Christo • Apr 2, 2008

Motorcycle magneto ignition


I have a small motorcycle engine, a single cylinder, two-stroke, 39cc blata 'replica' engine to be precise. This runs a simple magneto type system to produce spark at the right time to ignite the fuel in the combustion chamber. I am looking at the feasability of making a multi-cylinder engine of either 2 or three cylinders and wondering how I rig up the ignition system. In the case of a twin cylinder engine could I just mount a second coil at 180 degrees from the first one, as the coil has two pick-ups built-in which match the flywheel magnets? The magnets are cast into the external circumference of the flywheel. There is no battery in the system and no points. See image below.
Thanks in advance for helping me out.

gohm • Apr 6, 2008
Please post a pic and some more info on the system (output specs etc) & I'll try to help you. Without any details on the system I would normally guess one more cylinder would be max capacity. Will you also be running a battery? Is this a switchable system? What kind of points are used?
Christo • Apr 6, 2008
Thanks gohm,

The ignition is a 'pointless' system and has no battery.
It is merely a coil mounted adjacent to the flywheel, which
has a pair of small magnets on its circumference which I assume
not only generates a small spark but also when it should spark as well.
Do not know of the exact specs.
I will post a pic when I get home later,once I figure out how.
Christo • Apr 7, 2008
Image now added.
ph_kosel • Jul 10, 2008
I think you're on the right track as far as putting an extra coil next to the wheel, assuming the engine doesn't have opposed cylinders like a Honda Goldwing or an old BMW. A bigger problem might be finding a kick-start multi-cylinder bike, because with no battery you would need one. Most current multi cylinder bikes don't seem to have a kick start pedal.
geococeo • Aug 3, 2008
surely you can add an extra cylinder with stroke cycle 180 degrees out of sync with the first, and add another coil onto the magneto just the same, and BAM you got a two cylinder. now if you wanna get tricky tricky. i will presume with no prior knowledge, just instinct, that if three cylinders are 120 degrees out of sync on the crankshaft(120 deg difference in stroke cycle) then you should be able to mount the coils just the same, and same goes for 4cyl 90 degrees 5cyl 6cyl until you run out of physical room on the magneto. also a thing to think about when cylinders are not having 180 degree diffs in their stroke cyle is that the balance during operation can become a huge problem but whatever you got bigger fish to fry. please tell me what you decide to experiment with
aluminumfetish • Aug 31, 2008
Hey all, I ust registered and have similar questions... I have a yamaha RD350 that was a "points" bike. I've replaced the points with an aftermarket CDI. The RD is/(was) a type B charging system. The coils are fixed on the outside and inside spins an electromagnetic rotor. I've removed all of that and am running a bettery with no charging system. This is common is race bikes as most track races don't last long and the battery is removed and recharged after race.... If anyone has knowledge of this set up please mail me. I'll start a new post as soon as I get the hang of this site.Thanks, New guy.... MITCH
frankline11 • Sep 2, 2008
Most dirt bikes made before 1980 had points ignition ( but not all ! ) Most ( but not all ! ) of the two-stroke engines had fixed advance. That means there was no variable advance of the ignition timing.
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