GM Distributorless Coil Mod - Writeup
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  1. #1
    Supporting Member ryan.hope's Avatar
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    GM Distributorless Coil Mod - Writeup

    This guide details how to replace your old stock ignition coil with a more modern and powerful coil. Most of the users who have completed mod have experienced the following benefits: 1) more complete combustion (no longer will you smell like gas after a ride, 2) smoother power band across entire RPM range, and 3) slightly better low end torque.This modification applies to the 1978 thru 86 CM/CB 400/450 engines with CDI ignition and isn't applicable to a point ignition. It may apply to other CDI ignitions that use a .35-.55 ohm ignition coil.

    This mod was originally pioneered by coldfuzion76.

    Difficulty: Easy
    Time: 30-60min

    Part List
    • Duralast/Ignition Coil (Part Number: C849)
      For those not in the USA the part numbers are GM part number 10472401 or AC Delco # D555[/*:m:2ztvztil]
    • 2 x Male Faston/Fastin Connectors
      [/*:m:2ztvztil]
    • Liquid Electrical Tape[/*:m:2ztvztil]
    • Spark Plug Gap Tool[/*:m:2ztvztil]
    • Spark Plug Wire (long as possible)[/*:m:2ztvztil]
    • Miscellaneous Mounting Hardware[/*:m:2ztvztil]


    Procedure
    1. Remove seat and gas tank[/*:m:2ztvztil]
    2. Disconnect resistor caps from spark plugs[/*:m:2ztvztil]
    3. Unscrew resistor caps from spark plug wires[/*:m:2ztvztil]
    4. Remove spark plugs[/*:m:2ztvztil]
    5. Disconnect ignition coil from CDI unit[/*:m:2ztvztil]
    6. Remove ignition coil from frame[/*:m:2ztvztil]
    7. Cut off ignition coil wire harness (as close to coil as possible)
      [/*:m:2ztvztil]
    8. Crimp male Faston/Fastin connectors to ignition coil wire harness *alternative connection instructions in post #11*[/*:m:2ztvztil]
    9. Insert Faston/Fastin connectors into the slots on the bottom of new ignition coil*
      [/*:m:2ztvztil]
    10. Seal Faston/Fastin connectors with liquid electrical tape (cover all exposed metal), let dry[/*:m:2ztvztil]
    11. Cut spark plug wire in half approximately, measure out the long side first.[/*:m:2ztvztil]
    12. Screw resistor caps onto cut ends of new spark plug wire
      [/*:m:2ztvztil]
    13. Mount new ignition coil**
      or [/*:m:2ztvztil]
    14. Connect new ignition coil to CDI[/*:m:2ztvztil]
    15. Set spark plug gaps to .035in[/*:m:2ztvztil]
    16. Install spark plugs[/*:m:2ztvztil]
    17. Connect resistor caps to spark plugs[/*:m:2ztvztil]
    18. Replace seat and gas tank[/*:m:2ztvztil]


    Notes
    *It does not matter which side the green or yellow wire get connected, they both fire simultaneously.
    **I used pipe strapping since I had it lying around and it already had holes in it. Others have used L brackets to mount their coils. Mount the coil how ever you want.
    1982 CM450E Cafe/Brat Build
    1982 CM450E Partout!!!

    Vintage motorcycles are just like women. They're moody and mysterious, they require a lot of maintenance, and you want to ride them all.

  2. #2
    Supporting Member ryan.hope's Avatar
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    Re: GM Disributorless Coil Mod - Writeup

    I cleaned up the original post of this mod so that it could be made a sticky. I don't think I forgot anything but if you have any comments I will integrate them into the main post.
    1982 CM450E Cafe/Brat Build
    1982 CM450E Partout!!!

    Vintage motorcycles are just like women. They're moody and mysterious, they require a lot of maintenance, and you want to ride them all.

  3. #3
    Super Moderator longdistancerider's Avatar
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    Re: GM Disributorless Coil Mod - Writeup

    Nicely done, thank you.
    I edited #11 for clarification is all.
    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
    1972 CL350 survivor restoration

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  5. #4
    coldfuzion76's Avatar
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    Re: GM Disributorless Coil Mod - Writeup

    Cool write-up! I've seen this mod done several times now here, and over on Dotheton. Glad to see so many have benefited from it.

  6. #5
    MrMcTavish's Avatar
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    Re: GM Disributorless Coil Mod - Writeup

    Well since I was gonna replace my coil anyway why not do this
    1978 Cb400 Hawk II

  7. #6
    Senior Member xHoladay40x's Avatar
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    Re: GM Disributorless Coil Mod - Writeup

    im about to try this to my bike i have everything except the coil, ordering from my shop tomoro so goona do it this weekend, hopefully all turns out well
    Check out my 78 cb400 hawk rebuild ------ viewtopic.php?f=5&p=129641

    "In order to be old and wise, you first must be young and stupid"

  8. #7
    Senior Member xHoladay40x's Avatar
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    Re: GM Disributorless Coil Mod - Writeup

    ok so i bought the coil now i am trying to do it but no spark, is ther different size connectors cause the ones i am using i had to trim a little to get them to fit, someone please help i dont want to of just wasted my money on something that will probly never get used if i dont do it.
    Check out my 78 cb400 hawk rebuild ------ viewtopic.php?f=5&p=129641

    "In order to be old and wise, you first must be young and stupid"

  9. #8
    Senior Member HerrDeacon's Avatar
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    Re: GM Disributorless Coil Mod - Writeup

    Nice post Ryan, thanks for taking the time to write it up. Also, thanks to coldfuzion76 for the idea and initial thread on this topic. Should be a great benefit to a lot of members.
    Perry

    1972 Honda CB350
    / 1978 Honda XL250S / 1982 Honda MB5 / 2014 Honda CB500X

  10. #9
    Supporting Member crazypj's Avatar
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    Re: GM Disributorless Coil Mod - Writeup

    Quote Originally Posted by xHoladay40x
    ok so i bought the coil now i am trying to do it but no spark, is ther different size connectors cause the ones i am using i had to trim a little to get them to fit, someone please help i dont want to of just wasted my money on something that will probly never get used if i dont do it.
    Yes, the spade connectors come in various sizes. Auto parts shops usually only carry 1/4", I think you need 3/16"
    Try Radio Shack
    There are three types of people in the world, those who can count and those who can't
    I'm not a complete idiot, but, I'm working on it

  11. #10
    Supporting Member ryan.hope's Avatar
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    Re: GM Disributorless Coil Mod - Writeup

    Quote Originally Posted by crazypj
    Quote Originally Posted by xHoladay40x
    ok so i bought the coil now i am trying to do it but no spark, is ther different size connectors cause the ones i am using i had to trim a little to get them to fit, someone please help i dont want to of just wasted my money on something that will probly never get used if i dont do it.
    Yes, the spade connectors come in various sizes. Auto parts shops usually only carry 1/4", I think you need 3/16"
    Try Radio Shack
    Can always cut down a 1/4" with a tin snip or use a file on it till it fits.
    1982 CM450E Cafe/Brat Build
    1982 CM450E Partout!!!

    Vintage motorcycles are just like women. They're moody and mysterious, they require a lot of maintenance, and you want to ride them all.

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