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just bought the 82 xj750j on ebay with 16,000 miles

Discussion in 'XJ Technical Chat' started by ravenbut, Jul 6, 2021.

  1. ravenbut

    ravenbut New Member

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    its pretty sweet but i need some advice. it will not start unless the clutch is in and the big kickstand is down. weird right. also the neutral light does not work. any help would be appreciated. its really a cool bike.
     
  2. ColoradoDan

    ColoradoDan Active Member

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    Nice! With only 16k, she is a baby. First suggestion, check all the pinned posts in the technical sections that will walk you through the absolutely necessary work to perform. Don't fix the one problem. Fix them all
     
    Franz likes this.
  3. Minimutly

    Minimutly Well-Known Member

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    I would read through the technical section to get to know your safety relay circuits. I'm very much fix the fault in front of me first guy, anything else comes later.....
     
  4. ravenbut

    ravenbut New Member

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    i really appreciate it and happy riding!
     
  5. Minimutly

    Minimutly Well-Known Member

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    It's not that the neutral light isn't working - the safety circuit isn't seeing it, hence no start and no neutral light either. I don't know enough about the stand switch to advise, sorry.
     
  6. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    I’m at the pub waiting on dinner. I’ll post something helpful either later this evening or tomorrow. You definitely have a problem in the circuit that indicates to the TCI that the gearbox is in neutral. There is a list of potential causes, and several remedies depending on what the diagnosis process reveals. All are easy fixes.
     
  7. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    OK.
    The neutral light and igintion interlock both interact with one another, and have one common ground through the sky-blue wire in the main wiring harness. That wire has its final connection at the neutral switch on the bottom of the oil pan. When the engine is in neutral the switch closes to ground the sky blue wire, which illuminates the neutral light and sets the ignition interlock relay to allow the TCI do its job.

    For our purposes I'm ignoring the sidestand and clutch switches right now since those both seem to be working correctly. Though I do wonder what you mean by 'big kickstand." Are you referring to the center stand that lifts the rear wheel?

    Back to the problem of not starting in neutral.

    One of the more common problems foa a XJ that has either sat, or not had the oil changed in long time, is the buildup of sludge around the neutral switch. This prevents the switch from closing, thereby preventing the neutral light from illuminating and the bike from being able to start in neutral.
    The usual (and easiest) fix is to dose the existing oil with Seafoam in order to clear out the sludge. About an hour or two of riding should get it cleaned out, after which you will want to change the oil and filter.

    The second most common issue is a sky blue wire that has become unplugged, or broken. You will find connections for it in the headlight bucket, and under the engine on the left side. It's partially hidden by the lower frame rail and exhaust (thogugh the exhaust dose not pose as much of an issue on your model). The switch is in a deep well that can be difficult to see, so use a flashlight.. The wire has a split-ring terminal that is held to the neutral switch by a single JIS (crosshead) screw.

    The third, and least common problem is a misrouting of the wire that causes it to wear through and break. Save that one for last as you'll have to remove other parts to check the whole length of that wire.

    The only other thing that I can think of would be a problem with the relay, but I don't recall one failing in a way that would prevent from starting in neutral and allow starting with the clutch pulled in.


    Going back to needing to have the "big kickstand down": If indeed you are talking about the centerstand, then that makes me think that the problem does lie with a problem at the underside of the bike (the neutral switch itself, or a loose/broken wire). That stand has no interlock switch on it.
    If you are talking about the sidestand also needing to be down in order for it to start with the clutch pulled in, then you also have a problem with the clutch lever switch. It could just be that it has popped loose from the socket that holds it in place, or it may have broken from a spill. That switch is round, has two wires leading to it, and is located on the lower half of the clutch lever perch. There is a small hole on the underside of the perch that you will stick an unbent paperclip into in order to release the switch from the perch.
     
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  8. Minimutly

    Minimutly Well-Known Member

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    Good answer from k-moe. I'd start at the headlight.
     
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  9. ravenbut

    ravenbut New Member

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    thanks alot, i appreciate it very much. i will try that when i have time, now i have a stack of computers
    that i have to repair. i wish i could throw them all out in the yard and put my new "to me" xj in my shop
    to work on it. i did not expect to get this much help. after i bought it the po told me that it would not start
    unless the big stand was down and the clutch was pulled in but i soon realized it was the sidestand that has
    to be down.
     

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