Johnson LS37 coil conversion to electronic ignition

[seahuntboater]

Greetings.

I have been studying the posts on the forum regarding converting coils. If I convert I am not sure what coil to use to start with to mount on these laminations. Seems like some kind of military coil.
My engine is 1 cylinder and existing coil had 4 solder connections. Eventually I will need to figure out how to wire it up.

Has anybody ever used an electronic module vs keeping the points and condensor. I don’t know if they are 7/16 size hole, etc. What would be the issues? etc.

Also a general question. Doesn’t the size (width) of the coil matter as to when the magnet starts to build the charge in the coil? Does this distance affect the timing?

Lots to learn and I sure appreciate the knowledge and advice given to me and others.

• This topic was modified 3 years, 11 months ago by Mumbles.

[The Boat House]

• This reply was modified 3 years, 11 months ago by The Boat House.
• This reply was modified 3 years, 11 months ago by The Boat House.
• This reply was modified 3 years, 11 months ago by The Boat House.
• This reply was modified 3 years, 11 months ago by The Boat House.

[dave-bernard]

how about mounting a coil externally and use a battery?

[Mumbles]

The original LS-37 coil part number is 72-1045 but it seems Johnson recommended the 72-1072 two cylinder coil as a replacement when necessary. Your coil looks to be a two cylinder coil so the two solder tabs on top would be for the spark plug wires and the two leads coming out of it would be for the primary circuit and go to the points and ground. When used in a single cylinder application, one of the spark plug tabs would get wired directly to ground. Using a two cylinder coil in a single cylinder motor should generate a hotter spark as it only has to fire the one plug instead of two at the same time.

As for ignition modules, I have used the red Atom modules meant for outboard magnetos with great success. I’ve also tried the common Nova II modules but found they wouldn’t hold up and burned out in a short time. The Novas were tested in a 70’s two cylinder motor with strong Alnico magnets in the flywheel but they might, and I say might, work better in a pre war motor with iron magnets in the flywheel.

Here the red Atoms are installed in a ’40 Evinrude Zephyr and a ’60 McCulloch 12 horse.

[oldemtr]

dave-bernard wrote:

how about mounting a coil externally and use a battery?

You may or may not like the way that looks :

[seahuntboater]

Thanks but I do not want the do the battery idea on this motor.
I took all the old windings off the coil and now have just the plates.

Before I go ahead and try and just put in a coil retrofit I am wondering if there is any way to put in a magnetron ignition system that is the coil, points and condenser all in one. For example something on this picture concept but designed for under the flywheel (plates curved the other way) . Or is it possible to take something like this apart and then mount it on my armature plates. Or could the ears on the picture example just be cut and angled the other way? By the way my flywheel has 2 sets of magnets 180 degrees apart. Does that mean it was a flywheel from 2 cylinder? Will the 2 sets be a problem? Does a spark just get wasted or will I need a coil for two plugs and ground out one connection?

Thanks guys for the help and ideas .

[Author]

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