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Discussion Starter · #1 ·
I'm building a BSA unit single that has an electronic ignition and charging system that wants 5000 ohm resistance in the spark plug cap to protect the solid state voltage regulator. In pursuit of trickness I was thinking I might try a coil on plug or coil near plug set up. Is there going to be a problem with RFI messing up my regulator or does having the coil on plug not allow RFI to escape? Can I use a coil on plug coil wired like the original coil? It is much smaller that the can type originally fitted, is there some other amplification voltage wise in an automotive set up that is going to hinder the performance of a coil on plug coil on a motorcycle? Not sure who to ask about this stuff ,I was thinking of using an MSD two wire coil designed for a Ford application (8243).
 

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If memory serves me, when I worked at Chrysler the coil on plug or standard coils with plug wires ran a 4.7 uFd capacitor for noise suppression on 4 cylinder to 8 cylinder engines, but the injectors were included in the circuit. The capacitor should be on the 12V supply side and the body of the capacitor grounded. A single cylinder with no injector included will likely work better with a smaller cap, like 0.4uFD or so, but the value is also determined by the design of the ignition coil used. I'm sure MSD has a recommendation for their coil. As DanyR said, resistive plugs and ignition cables will help. Not dwelling coil more than is required for sufficient spark will also help. We had coils back then capable of 50KV and if you dwelled them to saturation, they would eventually punch through the cables or even the spark plug ceramic.
 

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Discussion Starter · #5 ·
Thank you for the responses, for my badly titled question. I was hoping to eliminate plug wires with the coil on plug, maybe resistor plugs are a good idea..Do coil on plug ignitions create RFI? I think I'll be safe and use a coil wire and cap.
 
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