Not Sure of Secondary Ignition Coil readings--1980 GS850G

[nate875]

Dear GS Lovers,

I have a 1980 GS850G that runs well about 30% of the time. The rest of the time I experience a significant loss of power. But when it runs well, I think it's really running strong. I got this bike running last fall after finishing a carb rebuild job and addressing air box leakage. The intermittent nature of my trouble got me thinking about the ignition system. I believe I may have two failed/failing ignition coils, but I'm not sure I trust the resistance readings. Here's what I got:

1-4 Secondary: wide open. No reading even at my meter's 20 million ohm setting.
2-3 Secondary: 8 million to 10 million ohms. No readings on lower-range meter settings.
1-4 Primary: 4.8 ohms.
2-3 Primary: 4.8 ohms.

My Suzuki factory repair manual says I should get approximately 4 ohms on the primaries, and about 15,000 ohms on the secondaries. So I'm calling primaries good. With the secondary readings showing open or nearly open, however, I am a bit surprised that the bike will start and run at all. I'm using a Fluke meter that has always been trustworthy, and I'm measuring from one spark plug terminal in the boot to the other. To get a good connection, I'm inserting a screw into each terminal that is the same diameter as the thread on the spark plug. I took these readings this past Sunday.

Since then it has dawned on me that the behavior of a coil failing open may depend on where the break is in the winding. If it's near the middle, maybe I still get spark at each plug, but it's weak--maybe about half of normal, since I would now have half the number of secondary winding turns available for each plug. If it is near one end of the winding, maybe I get little or no spark at the plug connected to that end, but I still get a pretty strong spark at the other one.

Please chime in, anyone who has some knowledge of these GS ignition systems. Let me know if you think there is something wrong in my coil testing methodology, or if you think my theory about their behavior when failed has any merit.

Thanks to all.

--Nate
1980 GS850G

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[tom203]

If you unscrew plug caps from a coils plug wires, and measure wire to wire you should see about 12000 ohms or so for a secondary reading. It's difficult to measure over old plug caps due to corrosion. Ignition coils are very durable. Do you have the stock ignition setup- with an ignitor??
it's more likely that you have a carb problem, or maybe fuel is not being delivered properly to carbs.

 

[nate875]

tom203,

Thanks for your reply and your guidance.

I believe I do have the stock electronic-style ignition setup, without points and capacitor.

On your advice, I started taking the plug caps, etc. out of the plug wires, and I'm finding some interesting things. The spring for #3 looked a little crusty with corrosion on one end, but otherwise the parts didn't look bad. The plug cap and spring for #2, however, are very dark and covered with either fine corrosion product, or possibly carbon/soot from arcing/burning. And I'm pretty sure I'm missing the little pin and disc for #2 that were present in #3. Either that, or they're still stuck in there and I'm not able to see them because it's so dirty. I took another resistance reading on this 2-3 coil with those parts out, and it has come down a lot, but it is still around 3-4 million ohms. It might be that #2 is so dirty down in the boot that I'm not getting a good connection.

I'm going to keep going on trying to get believable resistance readings on my coils, but the condition of #2 got me thinking about the idea of splicing on some automotive spark plug wires. Is that a crazy idea? Are there special things about this ignition system that will make it not work? Also, I didn't expect to get as many parts out of the boots as I did, so I didn't pay attention to the order in which they came out. I'll take apart the 1-4 wires and pay attention, but the condition of #2 makes me suspicious that these have been tampered with, and may not be assembled correctly. Do you know the sequence? I don't think this is addressed in my manual.

-Nate
1980 GS850G

 

[tom203]

Unscrew the plug caps from a coils plug wires- cut wires back 3/8 inch to expose fresh copper to your meter's probes. Stick probes in and look,for about 12000 ohms reading - this tests the coil's secondary fairly. New plug caps cost about $4 each, so don't waste your time fiddling with them as corrosion eats at them!

 

[nate875]

OK. I got it now. These motorcycle wires and boots (caps) are different from any automotive design I've seen. I unscrewed the caps that you are talking about, and now I'm getting these readings going directly from wire conductor to wire conductor:

1-4: 11,760 ohms
2-3: 11,600 ohms

These are lower than the 15,000 specified by my manual, but I think those readings indicate coils and wires that are still good. Tell me if I'm wrong.

I would like to put new caps on these wires as you suggest. Where are you finding them for $4? Bike Bandit says about $20 apiece. I know now that the huge resistance I'm seeing is in the caps, so I would like to see how it does with new ones before I go back to messing around with fuel/air/carburetion. I would really like to eliminate all ignition variables if I can.

I suspect now that the half-inch long pins I found in the caps when I took them apart are resistors. So do you know what the resistance through the entire cap is supposed to be, when all the parts are installed? And do you know what I should get specifically through each pin?

Thanks.

-Nate
1980GS850G


P.S. How do you like that 650L? I used to have a 550L.

 

[tom203]

Your ignition coils test fine. Lots of places sell caps, try Amazon or here's a typical set on on eBay....

http://www.ebay.com/itm/4-SUZUKI-GS...010-/311235893438?hash=item48771ad8be&vxp=mtr

You can get slightly shorter caps for outside cylinders if you are fussy unlike me.

this link from Basscliff explains terminology of ngk caps

http://www.sudco.com/spark.html

I like the 5k cap - stock ones were probably 10 k resistance wise.