pcream
XS400 Enthusiast
Hello all, I posted a previous thread about getting a stuck oil emulsion bolt from an '82 XS400XJ DOHC Seca, finally got it off and replaced it and the oil/filter. I had the bike running pretty well after cleaning out the carbs, but I was in the process of doing the MSF course and let the bike sit outside under a cover for several weeks. When I had some spare time after the course, I came out to do some practice riding around the neighbourhood and couldn't get it started. Ran down the battery, so I charged it up using a trickle and began troubleshooting.
Checking the spark plugs showed a spark only on the right side, none on left. Switching the spark plugs showed that the plugs are not faulty as the spark is still on the right. Switched caps as well and the same result, still firing on right, none on left. Checked the fuses, all still had continuity. I started looking at the diagram posted in the electrical section of the Seca manual posted here (first image) and tested the resistance. I went from left and right spark plug wire (wire going to ground from 9 on the image) to the orange, red/white, and gray wires that go out of the ignitor/TCI (8), getting resistance of ~9.1K ohms for each. That is within the tolerances in the manual for the secondary coils (7.9k +/- 20%). While checking this, I noticed that a black and white wire from the TCI was disconnected from another black and white wire coming from the harness (second picture). I thought I had found the problem, but when I connected it I lost all sparking on both sides! The diagram is not clear at all at what this wire does, it shows a B/W (black and white I assume, even though it's not in the color table) wire coming out of the TCI going to an unlabeled box (circled in the manual picture). What the heck is that box?
I'm not really sure what's going on here, I guess the next step is to check the pickup coils, but I'm suspicious of the TCI; it has a label sealing it dated to 2018 (last picture) and there is electrical tape wrapping all over the original wiring harness. I can't rule out the possibility of a short considering it was outside and it's been quite rainy here lately. Battery is holding at 12.6 volts, but goes to 9.6 or something when cranking, seems normal enough. Any help or advice is appreciated!
Checking the spark plugs showed a spark only on the right side, none on left. Switching the spark plugs showed that the plugs are not faulty as the spark is still on the right. Switched caps as well and the same result, still firing on right, none on left. Checked the fuses, all still had continuity. I started looking at the diagram posted in the electrical section of the Seca manual posted here (first image) and tested the resistance. I went from left and right spark plug wire (wire going to ground from 9 on the image) to the orange, red/white, and gray wires that go out of the ignitor/TCI (8), getting resistance of ~9.1K ohms for each. That is within the tolerances in the manual for the secondary coils (7.9k +/- 20%). While checking this, I noticed that a black and white wire from the TCI was disconnected from another black and white wire coming from the harness (second picture). I thought I had found the problem, but when I connected it I lost all sparking on both sides! The diagram is not clear at all at what this wire does, it shows a B/W (black and white I assume, even though it's not in the color table) wire coming out of the TCI going to an unlabeled box (circled in the manual picture). What the heck is that box?
I'm not really sure what's going on here, I guess the next step is to check the pickup coils, but I'm suspicious of the TCI; it has a label sealing it dated to 2018 (last picture) and there is electrical tape wrapping all over the original wiring harness. I can't rule out the possibility of a short considering it was outside and it's been quite rainy here lately. Battery is holding at 12.6 volts, but goes to 9.6 or something when cranking, seems normal enough. Any help or advice is appreciated!
