Magnetos - Late Qualcast Mowers

[Murphyv310]

The transistor has to be turned off to collapse the coil and give a spark. TBH, the circuit looks wrong, there must be more than a trigger winding or more circuitry.

[Cleggy]

Thanks for the comments; I've made some more measurements of the primary and I'm now more inclined to say its at least 0.7, possibly 1R .

A picture of the unit is attached. The only two wires from it are the EHT and the kill switch. Whatever electronics exist are within the potting, and hence my earlier comment that it is probably the case that the only way to test this is by substitution. The circuit I showed earlier is one I found on the web for the B&S three pole unit.

B

[Murphyv310]

Looks like a simple pick up coil type with a magneto type flywheel, same as Honda use on the GX engines, no electronics in the potting. Does it have an oil level switch, low oil or duff switch will disable the spark.
Assuming its a 4 stroke.

[Cleggy]

I'm not familiar with the Honda GX; is that a three-pole unit? I think it is the third pole which clinches the question of whether or not it has electronics; see attached.

[Murphyv310]

Hi.
The three pole types are used to give a certain amount of engine advance. Ideally you want the engine to start with the spark at just about TDC or marginally after TDC so you don't get kick back on the pull cord.
Once started you need to advance the ignition and at full revs even more advance, if you don't advance the ignition the engine can overheat.
I opened up a Honda one some years ago and it was very simple, the coil a couple of caps, diode and perhaps a transistor, it may have been a dual diode as it got damaged with the hammer on the dismantling process. I think the later solid state ones use hall IC's for timing and the firing of the coil and also use a simple capacitor discharge circuit.
I'd be inclined to test this on substitution.