Author Topic: CB750 coil upgrade?  (Read 2848 times)

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Offline slowjo

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CB750 coil upgrade?
« on: January 07, 2011, 02:43:39 pm »
I'm looking for a upgrade for my ignition coil. I would like to use a new coil that has removable sparkplug wires. This is to be used on a stock 1972 K1 CB750. I have searched the FAQ. Am I being ignorant thinking that a coil with removable plug wires will be better for my stock setup than a stock replacement?  The original ones have been working for the last 39 years. Or should I go with a OEM style coil? I'm thinking about upgrading my electronics before have to, on the side of the road.

Offline madmtnmotors

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Re: CB750 coil upgrade?
« Reply #1 on: January 07, 2011, 03:01:49 pm »
My Dyna coils work great. The only consideration is ignition type. I believe stock points use a different ohm rating than most electronic ignitions. I think stock points use 5ohm while many electronic ignitions use 3ohm, but this would need to be verified so don't just take my word on it. The coil manufacturer should be able to help and other, more knowledgeable members will likely chime in. I'm sure this information has been covered in previous posts.


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Offline Kong

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Re: CB750 coil upgrade?
« Reply #2 on: January 07, 2011, 03:16:15 pm »
Here's a link to some commonly asked questions about the Dyna systems.
2002 FXSTD/I  Softail Deuce
2001 Acura (Honda) CL Type-S
1986 Honda Rebel, 450
1978 Honda CB550K
1977 Honda CB550K

Offline Duke McDukiedook

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Re: CB750 coil upgrade?
« Reply #3 on: January 07, 2011, 03:23:47 pm »
5 ohm dynas will work fine if the cost doesn't hurt you too much.
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Offline TwoTired

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Re: CB750 coil upgrade?
« Reply #4 on: January 07, 2011, 03:52:33 pm »
Probably the only reason to replace the stock coils is when the output leads crack or are damaged.  It's pretty rare they fail internally without some sort of physical attack upon them.
They work quite well with the stock dwell on the points cam.  The stock ones are about 5 Ω.  So, if you retain points, keep the primary resistance at that rating.

Don't be fooled by claims that different coils will boost the spark voltage in a running engine and the ravings about all the wonderful "benefits".  That's just salesmen hawking their wares.

If you don't increase the engine's compression, higher spark voltage is unnecessary.  And, if you don't increase the spark gap, you won't realize more voltage at the spark gap. (assumes a Kettering type system (stock) that relies on the coils storing the energy.)

While a lower ohm primary coil may be capable of more voltage, it won't be realized in the SOHC4 due to the way the system works.  A lower ohm coil WILL consume more power from the bike's electrical, though.

Lloyd... (SOHC4 #11 Original Mail List)
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Offline slowjo

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Re: CB750 coil upgrade?
« Reply #5 on: January 07, 2011, 04:00:06 pm »
Thank you TwoTired. I have sent hondaman a PM asking him about the benefits of his transistorized box. I do not think I will change from original points system to a aftermarket electronic ignition.

Offline hcritz

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Re: CB750 coil upgrade?
« Reply #6 on: January 11, 2011, 08:13:09 am »
Hey Slowjo
I have one of Mark's magic boxes and it really does make the bike run better...def worth the cost. Very easy to install as well.

Offline slowjo

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Re: CB750 coil upgrade?
« Reply #7 on: January 11, 2011, 03:51:58 pm »
I just purchased one also. I'll have to wait till spring to try it out.