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79 GS550 coil meltdown

  • Thread starter Thread starter pmac
  • Start date Start date
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pmac

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So I was out for a ride last week when the power dropped as it was running on 2 cyl, when I pulled over I smelled burning plastic, removed the tank and found my left coil was melting near both of the mounting bolts. Brought the bike home on a trailer, got another coil and wired everything up. I have noticed that I do not get a regular voltage to either coil at this point. The bike seems to run fine but clearly there is an issue as the coil still gets hot after being hooked up to power for a half hour or more.

I assume there is a short somewhere, anyone have any suggestions that could help?

Cheers,
Preston
 
check for the 3-4 ohms of coil resistance, if you only have 1-2 ohms it will stress the points/ignitor. If so replace the coils; I'm assuming (I have no idea why) that you did not short the primary (O/W) on the coil coil to the frame.
 
pmac said:
So I was out for a ride last week when the power dropped as it was running on 2 cyl, when I pulled over I smelled burning plastic, removed the tank and found my left coil was melting near both of the mounting bolts. Brought the bike home on a trailer, got another coil and wired everything up. I have noticed that I do not get a regular voltage to either coil at this point. The bike seems to run fine but clearly there is an issue as the coil still gets hot after being hooked up to power for a half hour or more.

I assume there is a short somewhere, anyone have any suggestions that could help?

Cheers,
Preston
Click to expand...

I have noticed that I do not get a regular voltage to either coil at this point.

What voltage are you getting and are you measuring with the supply plugs disconnected ?

coil still gets hot after being hooked up to power for a half hour or more

Are you switching the ignition on a leaving the bike sit for that time ? Is the temperature to hot to touch or warm like a small charger. What is happening to the other coil?

As posplayr suggested measure the primary resistances. I'm guessing the replacement coil is not an exact match.

You coul measure the resistance between the old coil input wires and between each wire and the metal core. If you find a short that's one question answered.
 
Last edited:
Hi;
I had a similar problem few weeks ago, before leaving for holidays....
I saw that there was a spark between my points, so I changed the condensers, and it started directly without bogs, on the 4 cylinders..
Moreover, I replaced my old coils, by 1300 fjr coils, with a 3 ohm resistance and smaller than the old suzuki ones...

First you can check if there is a spark between your points, if yes, go for new condensers, a good ignition timing and check.. then go for change coils... :)

(sorry for the mistakes ,I'm french :) )
 
I have since changed out the points system for the Dyna s electronic ignition so the points are no longer an issue. I will have to check again when I return home from work as I have had the bike sitting in the garage since October. I was checking the voltage coming into the coils from the ignition system and it was fluctuating around but if I remember correctly around 10v. I believe it should be a steady around 12v is this correct? I'm going to do a bunch of work to the bike in February to get ready for the spring but this will be my first issue I want to tackle.

This is my first bike and am learning everything on the way so sorry for my lack of knowledge. The coil was definitely very hot to the touch, to the point where it was hard to keep my fingers on it for very long.
 
pmac said:
I was checking the voltage coming into the coils from the ignition system and it was fluctuating around but if I remember correctly around 10v. I believe it should be a steady around 12v is this correct?
Click to expand...

That depends. The way I measure coil supply voltage is, with the coil disconnected, measure the voltage at the supply plug.
In deciding what you should see at the coil plug you need to know what the source voltage is. Suppose you have a fully charged battery at 12.6 Volts and get 12 at the coil. That's about as close to perfect as you will get on a bike from the last Millenium. It's about the drop. The bigger the drop the less available to make sparks.
As the bike starts and revs up the source voltage could rise to 14 in which case the coil might see 13.5.
 
from what I have noticed on 2 different bikes with dyna s kits, the gs and the kz, once you throw a dyna on you will have a voltage drop. you may have to do a coil relay mod, I did on the kz. now, one thing you should check for is signal voltage at the signal input on the coils. you need to see between 1.2-1.4 vdc. if not, then you are seeing an issue with your dyna dropping one side on you. also, I would have replaced the coils in pairs, but that's just me. oh, and what coils are you running?
 
I am running a stock coil on one side and a used 3 ohm I got from a shop in town. Im having an issue timing my dyna currently as well as the test light is always 360? of rotation. Getting to the point where im considering rewiring the bike from scratch as I am kind of running out of ideas.
 
I'm running a Dyna on my '79. I suggest you talk to Dyna. You need the same impedance on both coils.
 
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