Phantom electrical issues on '83 KZ750H4, please help!?!

[markjs]

When I got the bike it needed an igniter and I got one off Ebay that seemed to work fine.

First it was fine but then after a while, every once in a while particularly when wet, it would lose one or two cylinders. Then it finally blew a coil completely.

I replaced it with a coil that was different (from a Yamaha XJ) but it was the same amp rating, and again it worked great. Then I washed the bike (at a car wash with hig pressure water and soap) and still it worked great.

Then after a few days sitting i take it for a ride and it's fine till it gets warm then it loses cylinders. At first I thought it was the other coil because it was those cyclinders, but then after it cooled it ran fine again for a while then it was the other two cyclinders that went dead. I cannot find any loose connections, at all. I have no idea how to test the ignitier but the coils test fine. I suppose if the coils were warm they may test differently but I have no idea how to make the happen other than to ride away and strand myself somewhere and then test. The thing is though the battery goes dead trying to restart the bike.

I HATE electrical problems. Always the hardest to diagnose and often the most expensive to fix!

[DiverRay]

Mark,
I would start with all the GROUND wires. you may be loosing the ground someplace because of oxidation or a slightly loose bolt. Check ALL ground wires!(usually black). Loosen the hold down screws or bolts, make sure everything is clean, and re-tighten the bolts.
Next check the gap between the pick up coils and the fire mechanism (metal tab that sticks out closes to the coil). IF the gap is supposed to be 0.008", set it to 0.004. This will allow it to produce more voltage, and a bigger spark at the coil.
Last thing would be the igniter you got from EBay. It could be failing when it gets hot. Try our fix on it, pull the cover, and reheat all the solder joints that you can.
Good Luck!!