Have a 1993 GS500 and the left cylinder is intermittent. I have pulled the wire off to verify that it was running only on on cyl. I have replaced the wire and caps,both sides, and still getting intermittent running. I have jiggled the wire but this did nothing, woundering if it could be a thermal problem. Has anyone had this problem before? Is there a way I can test the coil to verify it is good? Any suggestions will be great. Will be getting new plugs and try that but they loodo look fine.
Thanks!
Al

i had a cylinder down when the pilot jet was blocked completely

once i gave it enough throttle to get it up to 3-4k it woke up again

hold the plug against the head and you can see if it is sparking

I also had the same problem as Skirecs.  There have been reports of heat related failures of the crank trigger. Coil failures are rare but possible. And I don't recall any definitive failures of the CDI unit.

You can swap left and right coils to see if the problem moves with the coil.

Thanks for the input. I have gotten it up past 3-4k and its still intermittant, will verify when I get home.
Thanks!

Is the left plug wet with gas when u pull it ?  If so you know you're at least getting fuel ... if not then maybe carb problem .

Have you checked for spark while cranking, by pulling the left plug, ground it , and watch for blue spark ?  Use a known good plug - if no spark then troubleshoot for electrical prob.

All wiring and connections in the primary circuit should be checked - signal generator to igniter, igniter to coils, etc.   There's a circuit schematic on this site if you don't have a manual at home.

and btw the igniter can partially fail and give symptom u describe, but so can other causes - check the easy, cheaper stuff first .

In addition to all the excellent suggestions so far I'd like to add - Auxillary ground. Thin black wire from the negative terminal of the battery. It has a plug ~3 inches from the battery, and poor contact there can kill 1 cyl. Thing is though, in different bikes it usually is different cylinders.
Cool.
Buddha.

In addition to what buddha just said, if the thin ground cable is bad, you probably got one coil at the signal generator burnt....

You're gonna find it true if you swap spark coils and the problem persists on the same cylinder and the harness is OK.

Quote from: GAS on March 25, 2011, 06:48:59 AM
In addition to what buddha just said, if the thin ground cable is bad, you probably got one coil at the signal generator burnt....

You're gonna find it true if you swap spark coils and the problem persists on the same cylinder and the harness is OK.

Maybe not. I've had it have poor contact there and put it back in and coils and ignition box were fine.
Cool.
Buddha.

Thanks for all the info will be working on it this weekend and give update.

Thanks!
Al

Sorry for not getting back sooner.  Here is what I did:
1.   I verified that I did have spark on both sides.
2.   I did clean the connector that was on the negative terminal side.
So from the above it would appare that it is a fuel problem. So decided to do a few other tests.
3.   With both plug caps on I started the engine and pulled the left wire off and had no change in the rpm, about 3000.
4.   I then pulled the right one off and it would die, yes I did put the left one back on.
5.   I then started the bike with just the left plug wire on and the bike ran , rpm steady from about 1000-3000.
6.   I did this with the right one also with the same results.
It seems that with both plugs on only the right one will be constant, where the left will be intermittant.
My next step is to look at the wiring and clean the conntacts.
Any thoughts on what else I should do?
Thanks for all the help!
Al