79 GS850 - no spark on #3

[dbarnes42]

I have a 79 GS850 that is completly stock except for a Dyna S ignition, new coils and the coil relay mod. While riding yesterday, I noticed the bike started to become sluggish and would not accelerate as well. When I got home, I checked the timing, which was still spot on. I also noticed the #3 pipe was not very hot. I pulled the #3 plug, which had fuel on it. I grounded the plug to the engine and cranked it over. No spark. I took that plug and put it in the #2 wire and spark was blue and strong. I pulled the #2 plug and put it in the #3 wire and had no spark. I know that #2 and #3 use the same coil but is there something else I should look for? I dont think the coil is bad. Any ideas or suggestions?

[tkent02]

Look at the end of the spark plug wire where it comes out of the coil. I bought a barely running GS1000 with Dyna coils. Three of mine had a burnt end, lot of carbon in there, two rarely sparked, one never did. Whoever put the wires into the coil didn't do a very good job of it. Taking it apart, cleaning inside the hole in the coil, cutting off the end of the wire and putting it in correctly was all that was needed.

[dbarnes42]

I should add that when I replaced the coils, I did not use Dyna coils. I used new coils bought from Cycle Recycle in Indy. The plugs wires are hard mounted into the coil I think. I was thinking I should snip off a little bit where the wire goes into the plug boot and also check to see if that plug wire is shorted somewhere under the tank. Am I going in the right direction or should I look elsewhere?

[tkent02]

It has to be something along that wire.

[rustybronco]

Do you still use the original spark plug caps (ends/boots), the ones that use resistors in them?
if you still have them on it, look in the end where it snaps over the spark plug and you will see a screwdriver slot. lefty loosey it and see if the 13mm long resistor is still good.

[dbarnes42]

Dang! Another thing I forgot to add was that when I replaced the coils I replaced the boots with NGK boots also from Cycle Recycle.

[rustybronco]

they still have a resistor in the boot end.

[dbarnes42]

I will check that tonight. Is there a specific ohm reading I should get? Should I read the resistor by itself or through the boot? Or am I just checking to see if it is broken? Can I leave it out if it is bad?

[rustybronco]

I'm thinking 5K resistance should be about correct and read the value through the boot.

I'm not sure if it's removable...

[dbarnes42]

OK I measured the resistance of th boot and it was 4.9 ohms. Just out of curiosity, I swapped boots and there was still good spark on #2 and still none on #3. So I pulled the tank and began chasing the wire. I noticed the coil for #2 #3 was hot. I am sure this isnt good. Any suggestions on where to look or what to look for? I am guessing I have a bad connection or a short somewhere.

[dbarnes42]

This is where I am at. I pulled both coils off. I hooked up the original #2/#3 coil to the wiring for #1/#4 and the #1/#4 coil to the wiring for #2/#3. I still only had spark on 3 of the four leads. So my questions are these: 1. Is it possible for one side of the coil to go bad and 2. Does the coil get a ground through or from the bolts that attach it to the frame?

[earlfor]

OK I measured the resistance of th boot and it was 4.9 ohms. Just out of curiosity, I swapped boots and there was still good spark on #2 and still none on #3. So I pulled the tank and began chasing the wire. I noticed the coil for #2 #3 was hot. I am sure this isnt good. Any suggestions on where to look or what to look for? I am guessing I have a bad connection or a short somewhere.

The coil should not be hot. Best guess is an internal ground fault in the coil.
I would replace the coil.

Earl

[1978GS1000custom]

the coils ground might have been weak in the first place causing a pooling of power making it hot. once hot things inside can melt and loose contact. this happened to me on a different bike but the same problem. if your gonna replace the coils go dyna and be done with it. use dyna wires also. i got a set of new ones on ebay a few months ago for 60.00 plus shipping you just gotta keep looking and they always show up for sale. i have a stock set of 78 gs1000 coils left over from my upgrade if you need them send me a pm and we can work out something if they would fit.

[dbarnes42]

Here is an update - I went to get a new coil but Cycle Recycle is out right now. He gave me a "loaner" to use. Problem is fixed. I will be getting Dyna coils and wires asap. Thanks to everyone for their help.