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Aftermarket Coil

Points Based Ignition | Electronic Ignition Upgrade
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Tom Member
Posts: 1
Joined: Fri Aug 29, 2003 2:45 pm

Aftermarket Coil

Post by Tom » Fri Aug 29, 2003 2:53 pm

I have a 1967 CA77E Dream 305 with single point ignition. I have been having problems with the spark plug wires and as a result purchased an aftermarket coil and plug wires. It is a 3 ohm coil. After everything was installed, the coil heated and melted. The bike ran until this happened. The dealer wanted to know what the resistence is from the condenser. Can anyone help me with this information? I am looking for points, condenser and possibly a new coil. The coil prices are very expensive and so far only available from eroupe. I can get a Nology Coil in either a 3 ohm version or a 1/2 ohm version. Any help would be greatly appreciated.

mwhitebook Member
Posts: 1
Joined: Fri Sep 05, 2003 12:35 am

Re: Aftermarket Coil

Post by mwhitebook » Fri Sep 05, 2003 12:56 am

The 1/2-ohm Nology coil is not made for points ignition - it is for Capacitive Discharge ignition. The coil current would be much too high for your points (and for your charging system).<br /><br />The 3-ohm Nology coil is a fine little piece, but if you look at the Nology disclaimers regarding what ignition systems it may be used with and which it cannot be used with, you'll find they're pretty restrictive. The problem is it's size (which is also its attractive feature); it has little surface area to cool itself from the self-heating of the coil current and its own internal resistance. The longer the dwell (points-closed) time, the more it heats. I can't say that it won't work in your setup, because I don't know what it's &quot;dwell threshold&quot; is, but I have had the red potting melt down in some applications. The ignitions for which Nology approves its use all appear to have computer-controlled (short-duration) dwell times, which minimizes the self-heating, so no problems.<br /><br />The Dyna (KV Electronics) dual-tower coils come in 3-ohm (green) and 5-ohm (black) versions, and perform very well. The spark energy of the 5-ohm version should be more than you'll need for a softly-tuned bike like the CA77, and it will draw about as much current as the original stock Honda part (important, because the older Honda charging systems are barely up to the task). I have used both the 3-ohm and 5-ohm dual-tower parts on 650 Yamaha twins (360-degree crank w/waste spark), and they have performed flawlessly.<br /><br />Dyna has a good web site, and you can order retail directly from them.<br /><br />The dealer's interest in your condenser has to do with his suspicion that the condenser is continuing to draw current through the coil even when the points are open, which would lessen (or completely eliminate) the spark, and cause additional wasteful coil heat. The condenser should have a very, very high DC resistance; you'd need a good ohmeter to measure it accurately. There should be NO DC current through the coil when the points are open. By all means, replace the condenser with a new one before you install a new coil. If you need new points, now would be the time, too.<br /><br />Hope this helps. Good luck with your problem!<br /><br />

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