No Spark From Apparently Good Coil

[80GS750]

Now that I have my Kat running, I have started to work on my 1980 GS750. It quit on me last fall, and would not restart. I checked for spark, and found that cylinders 1 & 4 had it, but not 2 & 3. I thought the coil was bad, so I took it to the Rice Paddy in Columbus to get it tested. They checked it, and said it is good. I hooked up my multimeter to the plug where the coil is connected a few minutes ago, and got the following results:

2 & 3 coil: 10 volts with switch on and not cranking, 6.8 to 7 volts while cranking

1 & 4 coil: 11.3 volts with switch on and not cranking, 2.5 to 5 volts while cranking

Anyone got any ideas? The bike does not fire at all, but has spark on 1 and 4.

[Newbie2it]

Well, one easy freebie test to see if its the wiring on the bike or the coilpack.. Swap coils 1/4 where 2/3 is and then see if you still get spark. Put coil pack 2/3 where 1/4 is. Got spark now out of it? If not, you just narrowed it down to something in the wiring.. and if no spark, you just agian narrowed down the coil pack as possibly defective.

[80GS750]

Well, one easy freebie test to see if its the wiring on the bike or the coilpack.. Swap coils 1/4 where 2/3 is...

I thought about that, but Suzuki used a male connector on the 2/3 coil, and a female connector on the 1/4 coil. I'll have to make jumpers to make it work, and presumably make sure I get the polarity correct.

[GregS]

It would be cheap to make jumpers, you can get some crimp on connectors and wire at most auto stores or radio shack.
When you read your multimeter you want to see the voltage switch on and off. Problem is most meters don't react quick enough. You would need to also ohm check the pickup coils, compare the readings to see if 2/3 is vastly different.

[hardlydangerous]

I would swap the coils from 1-4 to 2-3 just for a quick test.

best though , to grab a manual and check the primary and secondary resistance of the coils.
If both are ok check the resistance of the pulse coil/signal generator.
if everything is ok with the pick ups and coils it's the CDI.
Unless that GS has points ignition but i doubt it. if it does change the points

[Newbie2it]

Nope no points, They got rid of them in either 78 or 79, the 80 is electronic simular to ours.

[80GS750]

Nope no points, They got rid of them in either 78 or 79, the 80 is electronic simular to ours.

Correct. I found a procedure in the manual (also found the manual!) to test the ignitor (CDI), but didn't get a chance to try it out last night. I'm hoping to have time to do it tonight. If that passes, I'll move on to the other components.

I have checked coil resistance before, both on this bike and on the Kat, and in both cases, got good primary readings and flaky secondary readings. Also, in both cases, I took the coils to The Rice Paddy to be tested, and they were shown to be good. The Rice Paddy has a little test bench setup that connects the coils to a power supply and the wires to a pair of spark plugs. Both coils had very good spark on the test bench. Needless to say, I don't have much confidence in my multimeter resistance checks.

Thanks for all the help so far.