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low tension mag starting

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Jim Sherman

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As long as your cam / crank gears are timed correctly the mag gear can go at any position. The mag is nothing more than an AC generator, it puts out a constant voltage as long as it is spinning and is just along for the ride on the cam gear. Think of it like a friction drive magneto (without external coil)that rides on a flywheel at no particular relation to the timing. Keep in mind this is not always the case with other style mags.
 
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Jim Sherman

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The above post is only intended for the question Mike had asked about timing the Splitdorf on his F&J.
 
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Jim Sherman

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I may be wrong on this I just read up on it and it may need to be timed to the gear, I didn't think it mattered. I marked my gears when I removed them and put it back in the same spot but I didn't think you had to do that because it is a generator puting out a constant voltage. My bad.
 
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Ralph Leonard

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Excellant recovery Jim, you got it back on track before we jumped on you like a hound dog on a biscuit, LOL Ralph in NC
 
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Jim Sherman

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I've seen that happen too many times in the past! I'm glad I was able to catch myself first.
 
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Russ Hughes

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If the low voltage magneto is a DC machine with a large number of commutator segments, supposedly it shouldnt make any difference how it is positioned relative to the flywheel, particularly if it is a friction wheel drive with the flywheel. It would be more important that the condition of the magneto be good and that the magneto magnet was fully charged.

If the low voltage magneto was gear driven and had less commutator segments, or was an AC machine, then the orientation of the magneto armatuer to the flywheel position could be more important. A two pole magneto produces the maximum output at only two positions of the rotation of the armature and it would be important that the magneto be aligned so that the maximum output of the magneto occures at the same time as the ignitor contacts open. Otherwise the engine might be hard starting on the magneto alone because it just doesn't put out enough juice to fire the engine at cranking speeds although it might run the engine once it has been started and is up to speed.
 
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Ken Majeski

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It is interesting to note that on the 2 1/2, 3, 4, and 5 hp Fuller and Johnson engines the magneto turns at crankshaft speed while on the larger engines it turns faster while the igniter still trips at the point of peak voltage. This also makes it easier to turn the 6 and 7 hp engine fast enough for ignition.
 
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