Re: some problems; johnson seahorse 4hp
(Regular Magneto Coils - Continuity Test)
(J. Reeves)
Checking the continuity of the ignition coils....... Have the ohm meter set to High Ohms.
Remove the primary wire from points. Remove the coil ground wire. You do not want either of these wires touching anything.
Connect the black lead of a ohm meter to the spark plug boot terminal, then with the red ohm meter lead, touch the ground wire of the coil.
Then touch (still with the red lead) the primary wire. You should get a reading on both touches (contacts). If not, check the spring terminal inside the rubber boots of the spark plug wire.
If there is no continuity between the secondary circuit (spark plug) wire and the primary or ground, remove the coil from the armature plate, then check the continuity directly between the prong within the coil (prong that the plug wire connects to) and the primary and ground. Poor or no continuity of a coil (or plug wire) is one reason for weak spark, s/plug fouling, or no spark.
(Magneto Coils Failing/Burning)
(J. Reeves)
The only reasons coils on a magneto ignition system would burn up every so often is that somehow there is a low amount of battery voltage being applied to them, or they are not aligned properly.
Whatever accessories that may be used, do not run their ground wire to the black wire or black/yellow wire ("M" Terminals) on the ignition switch, push button switch, whatever as those black wire leads to the primary circuit of the ignition coil(s).
Voltage TO any accessory also contains voltage FROM the accessory in its ground wire to complete the circuit. Have a fuse panel set up, or run those accessory ground wires directly to the negative terminal of the battery to keep those voltages away from the magneto system.
If no accessories exist but a ignition switch is being used, the switch may be faulty and allowing a small amount of voltage to travel from either the "B" or "A" terminal of the switch to one of the "M" terminals. That can be checked with a volt meter set to the lowest voltage setting.
If there are no accessories and no ignition switch, I'd suspect that the coils out of alignment. Have the metal vertical portion of the coil yokes aligned with the inside edge of the bevel that exists on the top portion of the aluminum seat upon which the coils sit, creating the proper distance between the coils and the flywheel magnets. Faulty alignment creats friction and the yokes of the coils heat up, turn blue usually, and expand.
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(Magneto Coil Alignment)
(J. Reeves)
To align the coils properly, have the metal vertical portion of the coil yokes aligned with the inside edge of the bevel that exists on the top portion of the aluminum seat upon which the coils sit. This creates the proper distance between the coils and the flywheel magnets. Faulty alignment creats friction and the yokes of the coils heat up, turn blue and expand.
