V4 Spark 

COP (Coil On Plug)

There has been a lot of interest in running coil-on-plug which is common on modern vehicles.  There are two problems to deal with in order to put them on our bikes - coil primary resistance and fitment.

Denso pencil coils with part numbers starting with 129700 seem to have been used a lot on stock bikes.  There are too many coils for me to try them all, and unfortunately, I have not found any lists giving part number/coil primary resistance/dimensions.  So, you will have to research if any particular coil other than those mentioned here will work.

If you would like a free and easy increase in total spark energy output, my coil testing has shown the output of the stock coils can be increased by upping the dwell time from the stock 4.0ms to 6.0ms (the 700's already have a stock dwell time of 6.0ms).

Coil Primary Resistance

These coils have a lower resistance than the stock, which means they will draw more current than stock and could over-heat and over-load the bike's electrical wiring.  One option is to wire the 2 coils in series, which adds their resistance together, but this also lowers the maximum potential total spark energy output by 35%.   While this may sound really bad, if you have enough energy to ignite and start the combustion, then I think it questionable how much gain there is to be had with having more energy.  And 65% of the COP coil output is still more that of the stock at 4.0ms dwell.  I have tried this coils-in-series on my bike and it ran fine, so at the very least, the spark energy was still plenty for an otherwise all-stock bike.  Plus there may be other benefits from the COP coils, such as they discharge faster which I think could mean an initially hotter spark.

The other solution to the lower resistance is shorting the dwell time (the time that the coil is charged) then the coils can be wired individually.  Starting with firmware version "e", there is an "Individual COP Dwell" config setting option for this.  This allows the coils to be wired without the previously called for ballast resistors.

The two wiring configurations are detailed below.  Here is a comparision of spark energy output (how this was measured): 

Individual COP, 2ms dwell

Series COP, 4ms dwell

OEM, 4ms dwell (stock)

OEM, 6ms dwell (extended)

You need to use coils with a primary resistance of about 1.4 ohms (or higher).  Coils with super lower 0.2-0.3 ohms can *NOT* be used.  Coils with a resistance of about 2.8 ohms would be ideal, but I have not seen any.

I have found some multimeters can be inaccurate when trying to measure low resistance.  To get around this, first measure the coil primary resistance, then take a measurement with the probes held together touching each other, and subtract this from the coil primary resistance measurement.  Or wire the coils (all the same part#) in a string and measure across all of them -

Again, then take a measurement with the probes held together touching each other and subtract this from the measurement across, and then divide that by 4 (or however many coils you strung together).  Also make sure your multimeter has a good battery.

If you know the original application for the coils (such as from an E-bay listing), you can search for a shop manual/wire schematic for that bike.  If one side of the coils is shown connected to ground, then it is pretty much guaranteed that the coils are the super low 0.2-0.3 ohm, and can *not* be used.  Else, the resistance might be OK, but you must check before using them.


I have tried Denso 129700-4400 & '5150.  Both are just short enough to fit on my '82 V45 Magna.  On top, just clears under the frame and up front, just fits under the radiator.  They are both 5" long.

I have no fitment info on other models, but as V65's are overall bigger bikes, I would think these or even slightly longer ones would fit.  If you want to measure the clearance on your bike, the top of this coil sits 4" above the threaded tip of the spark plug.

I have *not* checked this in person, but looking at E-bay pics, there appears to quite a few Denso 129700-* coils about this same length (but remember, you also want ones with 1.4 ohms primary resistance)

Longer coils seem to have this extra section between the main barrel and the rubber tip.

I have also tried *-4840 which has this extra section.  It is 1/2" longer and did *not* fit my '82 V45 Magna.

The connectors for these can be found on E-bay and other places such as here.

Denso 129700-4400

Denso 129700-5150

Wiring Configuration 1 - series (the easy way)

"COP option" is *not* required for this.  This can be done with both AL & OEM box versions.

Use 18 AWG wire

Wiring two 1.4 ohm coils in series yields 2.8 ohms together, which is the same as the stock coil, and draws the same amount of current as the stock coil.  As such, we can use the factory wiring and just connect to the spade terminals that connected on to the stock coils.  Use the stock 4.0ms dwell time. 

Maximum potential total spark energy output of the coils is reduced by 35% (but read above in Coil Primary Resistance).

Wiring Configuration 2 - individual

"COP option" is required for this.  Only available for the AL box version.


Wired this way, you can get the full potential total spark energy output of the coils.  Use at least 18 AWG for coil, battery, and ground wires.  The measured current draw of each coil is about 7 amps.  The relay keeps from passing additional current through the RUN/STOP switch.  You can get a universal 12VDC 40A SPST automotive accessory relay from an auto parts store or RadioShack.

Use firmware version "e" or later.  Check the "Individual COP Dwell" option and I recommend setting the Dwell Time to 2.5ms.

This is the cable break-out section shown in the diagram between the V4-spark module and bike harness connector.  This brings out the coil wires and ground so you don't have to hack up the bike harness.

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