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WinRice WinRice is offline
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Join Date: Jun 2005
Location: Colorado
Posts: 702
Coil-On-Plug 101



I bought several sets of COPís from Ebay to see what works and what doesnít. The ĎMade in Japaní Denso cops were used on several bikes around 2006-2007 and start with the number 129700-XXXX. The second set of numbers is what length and what type of seal grommet was supplied. All of the 129700 coils measured the same resistance, so they use the same internal coils and winding ratio.




What I found was two coils with large grommets that end in 4800 and 5100, where the length was exactly the same, but one grommet was deeper than the other. The 5100 had the deeper grommet and is from a 2006-2007 Suzuki GSXR-750. The Grommets actually interchange between the two, meaning you could use a 5100 grommet on a 4800 coil and itís the same. Left to right, you have a 5100 with a zip-tie used as a spacer, a stock 5100, and a stock 4800.




This how the 5100 with the zip-tie (about 3/16" wide) fits on a Denso Iridium IW24 plug (please excuse the nasty yellow valve cover). One thing to note, these coils only fit on plugs that have a removable terminal. In other words, the coils snap firmly on the bare threads of the terminal. Another thing to note, these are CDI coils which mean the primary to secondary coil ratio is less, because they were designed to be fired by approximately 400 volts from a CDI. If you try to fire these with 12 volts the spark will be very weak causing misfire. Some day I might make a more 'elegant' spacer, but the zip tie works pretty well for now.




M&W recommends these coils for their CD units, and sent this pic to show the correct polarity for wiring. Note that the coil in the pic is a 129700-3881 coil. The 3881 is just the length and grommet type, it's still from the 129700-XXXX family.
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Old 01-14-2014, 07:34 PM
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