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XJ700X timing mod

Discussion in 'XJ Modifications' started by Rallemikken, Jul 27, 2019.

  1. Rallemikken

    Rallemikken New Member

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    The pickups sits on a steel plate on the left side, and the plate is fixed with only two screws. I drilled two new holes, and removed the steel inbetween. This gave me the possibility to retard the timing 7,5 degrees. I settled on 6, and the bike became a dream to ride. No knocking, whatsoever, and I can take her up from 2000 rpm whenever I want. Anyone else tried this? Mileage seems the same. Maybe I've lost a few hp in the top, but don't miss them, to be frank.

    The stock ignition curve is a little weird. It drops up to 1500-2000 rpm, and then rises all the way up to 40 degrees. I suspect this is the reason why the idle speed is so troublesome to set on theese bikes. With my mod, this behavior is gone. Ignition is near TDC beyond this point. Considering replacing the ignition unit with one (or two, to be precise) without this "bump".
     
  2. Timbox

    Timbox Well-Known Member

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    Would be great to see that in a pic. I think it was Yamaha's way of having a very zippy cruising bike with the FZ head on it.
     
  3. Polock

    Polock Well-Known Member

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    i milled a slot in mine to advance the timing 4 deg and my butt dyno said it made no difference so i put it back, never thought about retarding it.
    if the carbs are set right it should pull 2000 rpm in fifth without any problem
     
  4. Rallemikken

    Rallemikken New Member

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    If I understand the Yamaha service manual, the tolerances of the TCI unit is big. At 2000 rpm, the advance can lie anywhere between 13 and 37 degrees. Correct me if I'm wrong, but this give some room for variations. My bike knocked with open throttle under 2500 rpm, and it felt nervous untill it reached 3000. Retarding made it more cultivated, and I can use the torque in the bottom.
     
  5. k-moe

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

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    It should not do that. Your ignition timing changes are masking some other problem.
     
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  6. Rallemikken

    Rallemikken New Member

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    Maybe an aggresive TCI, anyway, problem fixed. I never let my petrol engines run lean, and I never let them knock. Engine is ship-shape, pulls hard with wide open throttle from 1500 and up. Plugs looks nice, and valves adjusted last winter. Mileage between 0,55 and 0.6 litre / 10km. I'll upload the diagram in the manual I refered to. Up to 2500 rpm, a variation of 20 degrees are permitted. Can this be right? When you lit the plug at 37 degrees before TDC at 2000 rpm, I can't see how the engine can avoid knocking with open throttle. tenning.jpg
     
  7. k-moe

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

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    The service manuals have all sorts of errors in them. That could be one.
    My point is that Yamaha never let the engines knock either.
     
    Last edited: Jul 28, 2019
  8. FJ111200

    FJ111200 Active Member

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  9. squidx85

    squidx85 Member

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    I don't understand what you mean by this, or what this means. At 2000 rpm, maximum amount of intake vacuum, the advance is 37 degrees, at atmospheric, it's at 13? How does the ignition module work? I have an 85 maxim x, but am not familiar with that aspect of it, yet. I am familiar with cars and other engines, and a lot of theory behind tuning. I can tell you that a "tolerance" or "permitted variation" if you will, of 24 degrees is not correct. Even engines back in the 1960s, effectively had a 3d graph of ignition advance vs rpm and manifold pressure. Centrifugal and vacuum advance accomplished this before the era of 3d mapping with computer control.
     
  10. Rallemikken

    Rallemikken New Member

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    This TCI don't care about intake vacuum, no sensors. It knows where in the rotation it is (or more precise, it knows the point of LAST rotation) and it calculates the RPM based on time/rotation. Then it advance or retard the timing in correspondance to RPM only. Or at least, I think it's this way it's done. Very simple electrical layout. This is why some engines knocks on low RPM and open throttle. Mine did. 6 degrees overall retard did the trick. The whole curve moved down, but didn't change form.
     
  11. k-moe

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

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    The TCI doesn't calculate anything. The timing curve is fixed (and isn't really a curve). There is likely a problem with your TCI. Maybe a failing transistor, or bad caps.

    http://www.jetav8r.com/Vision/IgnitionFAQ.html#a7p2

    While written for the Yamaha Vision, the XJ TCI is nearly identical.
     
    Last edited: Jul 29, 2019
  12. Rallemikken

    Rallemikken New Member

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    It doesn't "calculate" in a binary way, but it is an active unit. It triggers the coil by cutting the current, like an old-fashion breaker point. It does so a little bit earlier as the RPM's rise. Something is definitly going on in there! I suspect the drop in advance from 2500-3000 RPM is due to the technical limitations of the box. We are speaking about electronics from the mid 80's. No logical reason, that I can see.
     
  13. Timbox

    Timbox Well-Known Member

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    Looking for the popcorn icon...
     
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  14. k-moe

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

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    I guess I don't know anything about 80's electronics. Ya know, the stuff that was cutting-edge when I was learning about electronics theory and application.
    I'll bow out and let the reverse-engineering happen. It is a fun way of learning, and I've done it myself.

    The fact still remains that if the engine was knocking with the stock spark timing, something was wrong. And to be clear, advancing the base timing is not a bad thing. I've done that to our Miata, however the goal was to tweak power delivery a little, not to solve a knock.
     
    Last edited: Jul 29, 2019
  15. Polock

    Polock Well-Known Member

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    did you ever put a degree wheel and a timing light on it to see where it is/was ?
     
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  16. squidx85

    squidx85 Member

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    Well, if it's rpm dependent only, with no intake/manifold pressure/throttle reference (a terrible design) the timing at light load would be far from ideal, (way too little advance to be efficient) since it would have to be tuned for mbt @wot, realistically slightly less to avoid knock. Every car I know of even in the 80s had vacuum and centrifugal advance. If all this info is true, and I'm not saying it isn't, the maxim would get a Lot better mpg with vacuum advance, or a proper timing curve.

    But that's theory, and they did what they did back then. Real world, if the motor is knocking and all stock with good fuel, as been written already, something isn't right.
     
  17. Polock

    Polock Well-Known Member

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    some used vacuum to retard the advance
     
  18. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    XJ650 Turbo, XS1100, and XJ1100's used a vacuum sensor (as did many later models, FJ1100/1200, etc.). But typically the purpose of the vacuum unit is to slightly retard the timing in the presence of high vac conditions

    From a well-known source:

     
  19. Rallemikken

    Rallemikken New Member

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    Did a check with a lamp, but didn't bother to glue on a wheel. Idle not far from mark, and then a sudden rise up to 2500 to 3000 RPM, just as expected, and as the curve says. Then it actually flattened out, maybe with a little dip as revs increased. Hard to tell.
     
  20. Polock

    Polock Well-Known Member

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    without numbers it's hard to say what happened. maybe the tci was out of spec before, for some reason, and you put it back into spec.
    the main thing is you like how it runs now and that's whats important
     

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