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Old 06-27-2021, 06:47 PM
TomH TomH is offline
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Replacing External Resistance Coil with Internal Resistance Coil

I am new to Atomic 4 engines, and attempting to replace the old (rusting) coil with a new one from Moyer. Though the old coil is printed with “use with external resistor” (and has a resistance across the (+) and (-) terminals of 1.3 Ohms) I’m unable to find an external resistor. I have some idea of what the resistor should look like, though if it’s an original part made of Bakelite or something, I might not recognize it.

I assume I need to remove the external resistor from the circuit before installing the coil with internal resistance from Moyer (3.5 Ohm resistance).

After replacing the coil, I also want to upgrade to electronic ignition (I already have the Petronix Ignitor kit).

Tips and advice will be much appreciated in tracking down the resistor.

I have four wires coming off the positive terminal of the old coil. One to the alternator, one to the starter, one to the electric fuel pump, and the fourth elsewhere in the boat (the ignition switch?). The negative terminal connects to the points.

Can I just install the new coil (and electronic ignition) as if there is no external resistor?

Thank you.
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Old 06-27-2021, 07:51 PM
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ronstory ronstory is offline
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Welcome to the forum.

The resistor normally looks like a long lego made out of ceramic and having wires or terminal on it. it usually measure out 1.5-2.0 ohms-ish. To see if you had one, just follow the wires upstream from the + terminal of the coil. If you don't have one, with points it would likely "still work" but you would be stressing the coil and the rest of the electrical components.

When you flip to the IE, the total current cannot exceed 4 amps for the Ignitor module in a 4 cylinder motor configuration. Also, the coil from Moyer (MMI) is actually seems to be more like 3.8-4.0 ohms which reduces the coil current.

If you use an aftermarket like NAPA IC14SB, it's roughly 3.25 ohms so you can be at or over the limit of 4 amps at idle with a ~14V set alternator. My recommendation is just get the MMI coil, it only $10-15 more and you won't need to worry about it. Or just add a ballast resistor with the coil you have.
Portland, OR

Last edited by ronstory; 06-27-2021 at 07:53 PM. Reason: format, typos, etc
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Old 06-27-2021, 08:32 PM
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You should be able to pick up a resistor at NAPA auto parts. I picked one up, oh, it must be 10 yrs back and still on the same resistor and coil.

Edit> Ron has you covered off in the previous post, that's what I put in and it's still there.

1976 C&C 30 MKI

The pessimist complains about the wind.
The optimist expects it to change.
The realist adjusts the sails.
...Sir William Arthur Ward.

Last edited by Mo; 06-27-2021 at 08:35 PM.
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Old 07-13-2021, 10:19 AM
Borrowed Time Borrowed Time is offline
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Coils & Pertronix EI

My upgrade to electronic ignition gave me all sorts of trouble with engine shutdowns by trying to keep cost down with a cheap auto parts store coil. All those problems ended when I bought Don's coil matched to a Petronix EI.

Some folks swear by their old reliable points, but I have not touched my EI since I installed it 6 or 7 years ago and once I switched out the coil, random shutdowns ended.
Borrowed Time
1974 Newport 27 with Original "Atomic" Power
Los Angeles, California
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coil, ignition, resistor, wiring

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