The first thing I would check is the plug wires and "boots" themselves. If the wires and boots are good, check *carefully* how they are attached to the ignition coils... the old `86 I owned developed an erratic spark that was a result of corrosion and crud collecting in the "sockets" of the coils where the wires attach. While you've got the tank off, test the coils themselves and also see if they are getting a signal from the wiring harness to fire. There is also a "pickup coil" underneath the cover on the right side of your engine, in front of the clutch cover... those can go bad, but I'd check the wiring harness here... I think the shop manual describes a procedure for testing the pickup coils too. If all of that checks out OK, the igniter (mounted under the seat near the battery) is the next thing I'd look at. I can't think of anything else that can cause the problem. Good luck!
Uh, actually I did think of something else. Electronic ignition boxes will sometimes fail to produce a spark if the battery voltage is low... it can be high enough to spin the starter motor, but still fail to produce a spark if you have one cell gone bad in the battery. Check the voltage on the battery, if it's below 11.5 volts or so, that's the likely culprit.
Right. I've checked the wiring from the pickups on the engine, up past the ECU box, to the switches. Nothing. The only thing I found was a small oil leak near the pickups. I think it might be something to do with that but I've got no way of testing them. Anyone know how to carry out tests on the pickups, ECU and coils? (I don't think it's the coils though 'cause they bth stopped sparking at the same time)
OK, keep in mind that this stuff is from the manual for an `89 1100... but I suspect the testing procedures and values are the same for all the oil-coolers... You'll also need the suzuki tester to check the igniter according to this. If it were me, and I knew someone close by with the same bike, I'd see if I couldn't talk him/her into letting me test my igniter in their bike. YMMV, but here it is: