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Discussion Starter · #1 ·
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.
 

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Discussion Starter · #2 ·
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.
 

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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 :D :D :D
 

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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.
 

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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.
 

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Re: GM Disributorless Coil Mod - Writeup

xHoladay40x said:
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
 

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Discussion Starter · #10 ·
Re: GM Disributorless Coil Mod - Writeup

crazypj said:
xHoladay40x said:
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.
 

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Re: GM Disributorless Coil Mod - Writeup

i decided to modify the gm coil so the wires come out the front instead of the back, so it could be mounted flush to a bracket

[attachment=0:1pmxsek3]2012-10-23 08.43.10.jpg[/attachment:1pmxsek3]

all it took was drilling straight through, there's nothing there, just plastic.. and you'll find some metal strips which were attached to the spade terminals. they seem to take well to soldering..

[attachment=1:1pmxsek3]2012-10-23 08.42.59.jpg[/attachment:1pmxsek3]

poured a little liquid neoprene in the holes for protection

if anyone wants a black coil like this one (instead of grey/blue/red like most of the aftermarket ones are) -- standard part# DR39T. it's cheap, payed $30 for this one..
 

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Re: GM Disributorless Coil Mod - Writeup

steveo said:
i decided to modify the gm coil so the wires come out the front instead of the back, so it could be mounted flush to a bracket

[attachment=0:fpyooh48]2012-10-23 08.43.10.jpg[/attachment:fpyooh48]

all it took was drilling straight through, there's nothing there, just plastic.. and you'll find some metal strips which were attached to the spade terminals. they seem to take well to soldering..

[attachment=1:fpyooh48]2012-10-23 08.42.59.jpg[/attachment:fpyooh48]

poured a little liquid neoprene in the holes for protection

if anyone wants a black coil like this one (instead of grey/blue/red like most of the aftermarket ones are) -- standard part# DR39T. it's cheap, payed $30 for this one..
how far did you need to drill i am thinking of doing it like this
 

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Re: GM Disributorless Coil Mod - Writeup

all the way, you need to solder through the back, but poke the wires through the front..

i broke both of the the flimsy spade terminals off while drilling, but the wire that attaches to the spade can be dug out with a little carving away of plastic, then just solder your wire to it and fill the hole
 

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Re: GM Disributorless Coil Mod - Writeup

I am not sure what the resistor cap is for. You can't just connect a straight spark plug wire from the new coil to the plug? What would it do if you did? And last question, what exactly does the resistor cap do?
 

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Re: GM Disributorless Coil Mod - Writeup

Paul1217 said:
I am not sure what the resistor cap is for. You can't just connect a straight spark plug wire from the new coil to the plug? What would it do if you did? And last question, what exactly does the resistor cap do?
This might answer some of your questions. http://www.motorcycleproject.com/motorc ... etech.html
Yes, you could use a automotive plug connector if you add the screw on cap to the plug so you get a solid connection. Means you have to switch it over everytime you swap plugs since MC plugs come set up for the clip style connectors.
 

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Re: GM Disributorless Coil Mod - Writeup

Making a mount for the coil was actually alot easier then i thought i used a flat piece of steel and used 1 of the stock mounting holes and bolt i made a sleeve to fit the coil to run a longer bolt though so it tightens down to the plate heres a pic of mine ive cleaned it up since this was a mock up but works well. Definitely a good mod to do for sure and fairly cheap.



 

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Discussion Starter · #20 ·
Re: GM Disributorless Coil Mod - Writeup

Paul1217 said:
I am not sure what the resistor cap is for. You can't just connect a straight spark plug wire from the new coil to the plug? What would it do if you did? And last question, what exactly does the resistor cap do?
The "resistor" in the term resistor cap refers to the spark plug so the resistor cap is essentially the connector that attaches the spark plug wire with the spark plug... it helps to differentiate this end from the end that attaches to the distributor/coil.
 
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