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1959 Mercury Mark 35a - Rewire Magneto to work off battery?

Boatsnhoes

Contributing Member
Hi all,

New member here. I bought a 1959 Mercury Mark 35a in non-working condition. I've been running through the systems one by one and thought I had everything in place. Pulled the starter and got nothing.

I suspect it may be due to weak spark since the magneto is so old.

I tested the magneto without a battery attached before trying to start - all the plugs get a blue spark without issue just from spinning the magneto by hand. Order is correct. I just don't think it's a strong enough spark because I can't think of what else it is (compression is good carbs are clean yada yada).

The magneto generates an electric field (supposed to be 12V) which is used to feed the ignition coil, but it also seems to have a terminal where a positive wire can be connected as part of that same circuit. This is where the question comes in: can I just connect a 12V battery to that lead and bypass the magnetic generator part of this entirely? That way I can be sure the coil is getting 12 strong volts when the points (aka breakers) open up, and my spark is as strong as can be.

The terminal in question is shown in this video (click link and it'll bring you to the right time, 1:58 or so) https://youtu.be/d_il7Q7N14o?t=112
It's the terminal where the white haired guy attaches the red lead. They also make some sort of a comment about a switch that I don't understand. I guess what I'm asking is what is supposed to be there? A positive lead from the battery? They mention a switch of some sort?


I looked around and didn't see any examples of others wiring a battery directly, but it seems like it should work.

If anyone else has tips any other tips at all on getting this kind of motor going I'm all ears.

Thanks! Glad to have finally joined. Thanks to Dangar Marine on YouTube for the recommendation.
 
The ignition switch grounds the mag to kill it. he doesn't have his key switch/wiring attached. The wires he attaches are for a bleeper, point close and it beeps. Attaching 12V to the mag terminal will damage it.
 
Those magnetos are very well engineered , very reliable.-----There is no need to try and use 12 volts anywhere near that unit !!!!
 
Thanks for the heads up guys. I won't attach any batteries.

Just to satisfy my curiosity, why would attaching the battery hurt it? It seems all the battery would do is replace the electricity generated by the permanent magnets in the magneto. Points and coil would still operate as normal.
 
You totally misunderstand how this unit works !-----Just 4 screws remove the bottm part of this magneto.----Do that and clean and set breaker points to 0.010".-----Test for spark before re-assembly to the motor.-----Do not attempt to use 12 volts on this thing !----Careful with the cap and rotor as they are big $$-----Have more than 1 of these white Mercury motors myself.
 
Listen to the above good advise!

You probably have fouled plugs, which magneto ignitions have a tough time overcoming. Clean them good with Cut Finder (aka lacquer thinner) and spin the motor over with them out to clear out the cylinders. Then try a shot of ether (starting fluid) and see if that helps. Don't go nuts with the ether however!

Jeff
 
You totally misunderstand how this unit works !-----Just 4 screws remove the bottm part of this magneto.----Do that and clean and set breaker points to 0.010".-----Test for spark before re-assembly to the motor.-----Do not attempt to use 12 volts on this thing !----Careful with the cap and rotor as they are big $$-----Have more than 1 of these white Mercury motors myself.

What am I misunderstanding? I'm trying to replace the electricity generated by the magneto's permanent magnets with an outside source. Shouldn't that be possible?

I already did all that stuff and as I said, it gets spark, I just don't think it's strong enough.
 
Listen to the above good advise!

You probably have fouled plugs, which magneto ignitions have a tough time overcoming. Clean them good with Cut Finder (aka lacquer thinner) and spin the motor over with them out to clear out the cylinders. Then try a shot of ether (starting fluid) and see if that helps. Don't go nuts with the ether however!

Jeff

Plugs are brand new so I don't think that's it. Ether definitely sounds like a good call. I'll give that a try.

I'm also going to attach the starter motor and just use that instead of trying to pull start.

Still curious about that magneto question though.
 
New plugs can (and will) foul as well!

Jeff

PS: On the later, CDI fired ignitions with individual coils, I tried to test one of these coils with a 12 volt battery. Didn't make any spark, which is not surprising since the system delivers 200 volts to the coils! (The stator puts out 400 volts to the switch box.) Not sure what voltage those old Kiekaefer mags put out, but it might be far more than 12 volts (or less, which means you would fire parts with a battery attached).
 
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Duly noted, thank you. I forget where I heard that the permanent magnets were supposed to supply 12V to the coil. So who knows, that could be off.

Regardless I won't be attaching a battery any time soon. The sparks I'm getting are blue and consistent, so it's back to the drawing board for me.
 
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