Misfire - Electrical Issue

A few months ago I purchased an '83 XJ750, non-working. It's original problem was a "misfire" where only one ignition coil would work at a time. The P.O. believed it was the ignitor and purchased multiple replacements. Oddly, switching between ignitors, would switch the the igition coil malfunction. This lead us to believe, that the ignition coils are OK, and we had multiple bad ignitors. While cleaning the electrical connections I found a corroded wire and pin in the rectifier, we repaired that and, the bike started right up. I contiuned with mechanical maintance, and the bike was in fine riding condition.

I took it on a long ride and parked it in the driveway. When I tried to start it again, back to the original problem. Due to a my error, I overtorqued the battery terminal and cracked a cell, replaced it. The diode behind the headlight failed, and I replaced it. I checked the rectifiers diodes, OK. Connectivity to the rectifier and battery, OK. I'm not sure where to look anymore. My next step is to check all the diodes in the harness, but before I do, I was hoping maybe someone had some helpful experience or insight.

Thanks,
Mike

 

Lets start at the original fuse block. Has it been replaced??
These are known to cause many electrical problems. The clips get brittle, and break.

The next step would be to check the entire wiring harness for Corroded/Loose/Dirty connections. That includes the spaghetti bowl mess in the headlight bucket.

After the wiring harness is squared away. You will need to progress onto the handle bar, and ignition switches. Male sure the contacts are clean,and working properly.

By the time you complete everything above. Your electrical gremlins should be well under control.

Ghost

 

The fuse box was replaced by the PO with individual inline fuses.

I checked nearly every connection, resistance, and diode and found nothing wrong.

When playing around in the handlebars the only thing that didn't work properly is the clutch switch, and the flasher relay/ canceling unit ( the left blinker doesn't blink at idol). But inspecting the wiring diagram that is a separate system. I can see that causing the issue.

What I did find seems to be bad TCI boxes. When I first got the bike, and trusting the PO I assumed they were all bad. When I discovered the bad rectifier and the problem went away I never bothered to check the other TCIs against the one that was already in and working properly.

From a lot of sources I have heard that it is very unlikely that a TCI would be the problem. I have 4 of them 3 OEM and 1 aftermarket (hyperpack s/n 3012398). When none seemed to work I assumed they couldn't all be bad. I plugged each one in and push started the bike (engine was flooded) until one of the OEMs started the bike on all 4 cylinders. Then plugged them each back in and tested the leads to every spark plug. 2 of the OEMs, including the one that ran the bike for months, had a bad channel, and the aftermarket seems to not work at all.

This leads me to believe they were all Ok, for the most part, and that something on my bike, is causing them to go bad. What do you think it could be?

 

I took the bike out for an hour or so and bike ran great. Stopped half way at wawa for a quick snack, couldnt have been off for 5 minutes, and the bike started right back up. However, when i got back home, parked it, and half an hour later tried to start it, problem came back. No spark in 1 & 4. I quickly checked battery, 12.8 Volts.

I have no idea where to look anymore.

 

The fact that the problem is common to #1 AND #4 indicates a coil or coil-circuitry-wiring related issue (including pickups.) The same coil fires 1 and 4, the other fires 2/3.

 

However, if I install one of the other TCIs, cyilinders 2 and 3 fire and 1 and 4 give me nothing. I have an aftermarket TCI ( hyperpack s/n 3012398 ) which will fire neither coils, then periodically fire both.

 

I think I've narrowed it down to the pick-up coils... When the bike is running properly I read 710 and 730 on the two coils. When it's not running They both read about 330 and are identical. This to me sounds like the 2 coils are shorting to eachother, ( parallel instead of series). This would explain why only 1 set of cylinders fires, and why the resistance changes. What I can't figure out is what would cause this, once the bike gets hot... Any ideas?