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'82 Seca left cylinder not firing/electrical problems

Discussion in 'The Garage' started by pcream, Jun 4, 2019.

  1. pcream

    pcream XS400 Member

    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!

    Attached Files:

  2. pcream

    pcream XS400 Member


    Checked the pickup coils' resistance going to the TCI, both within spec. Must be the TCI, went ahead and removed it and opened up the panel, had a lot of corrosion on bottom connectors, like water had gotten into it! It was always under a cover so I don't know how the hell water could have gotten in, unless it condensated or something. I clean it out the contacts with isopropyl, but I can't get to the actual components on the other side of the board. I tried removing the two nuts as well as the screws going into the metal cover on the back, but the board is fragile and I don't want to pry too hard. I went ahead and ordered another 82 Seca TCI on ebay, hoping I don't get screwed, they're all used and no one makes replacements.

    Attached Files:

    buztabuzt likes this.
  3. XSLeo

    XSLeo XS400 Junkie

    The extra Black/white wire was used along with some relays and switches to prevent you from riding with the side stand down.
    The bike should only start in neutral or the clutch pulled in. Once running if you put the bike in gear without lifting side stand that B/W wire gets grounded and the ignition stops.
    I would leave that wire unhooked.
    pcream likes this.
  4. pcream

    pcream XS400 Member

    Ahhh, perhaps the side stand switch is broken then, as it's been on the center stand the whole time. I've just received the "new" TDI/ignitor unit from ebay, I'll see if the problem is fixed when I replace the old one.
  5. pcream

    pcream XS400 Member

    Yep, new ignitor fixed the problem, spark on both sides. Filled the carb with fuel and it started up nicely after a couple of cranks. Next thing on the list is adjusting the clutch. It immediately starts turning the wheel when on the center stand and shifted into first from neutral.

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