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Ignition Coil Resistance & Caps

Discussion in 'XJ Technical Chat' started by fiveofakind, Oct 14, 2014.

  1. fiveofakind

    fiveofakind Well-Known Member

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    I have been running non resistor plugs NGK BP7ES...my plug wires test out at 11k plus each new cap is 5k each for a total of 21k per coil.....

    Bike is running great & I have been having a lot of fun enjoying it once again after a long restoration period.

    However, I notice in the Parts Diagram under Service Data for the XJ750J (15R)

    Under Ignition System: Spark Plug Gap/Torque/Cap.....it indicates that Cylinders 1 & 4 should be a 5k cap & that Cylinders 2&3 should be a 10k cap.

    However, everything I have read here in this forum including some Chacal literature, suggests one should use 5k caps on all cyclinders on a 1982 XJ750J Maxim or Seca.......

    So question is: which is it ? 5k or 10k on cyclinders 2 & 3 ????

    or does it not much much difference if bike is running fine....

    Just curious as to others opinion

    [​IMG]
     
    fiveofakind, Oct 14, 2014
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  2. fiveofakind

    fiveofakind Well-Known Member

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    what no answers here.....lol.....I know Bigfitz will answer.....
     
    fiveofakind, Oct 14, 2014
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  3. wizard

    wizard Active Member

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    You can run non R without a problem.
     
    wizard, Oct 15, 2014
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  4. fiveofakind

    fiveofakind Well-Known Member

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    what does that mean...not sure what your comment meant......the bike calls for "non-resistor plugs".....& that's what one should use on these bikes....

    My question was: what about caps on wires 2 & 3........5k or 10k caps ?

    Right now, I am running 21k ( 11k +5k +5k = 21k ) on both coils....

    However, parts catalog indicates 5k on 1 & 4 and 10k caps on 2 & 3 ...which would be 31K ( 11k + 10k + 10k )
     
    fiveofakind, Oct 15, 2014
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  5. Rooster53

    Rooster53 Well-Known Member Premium Member

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    Checked the FSM that I have and it has the same values you listed. However, I measured 2 to 3 and read 21.5K ohms, indicating the caps are 5K ohms ohm - I know these are original. Also checked a spare coil assembly for 2 and 3, and got the same 21.5K ohm reading, these caps also appear to be original and 5K ohms.

    Also from Len, I think you might have seen this already but just in case:

    It is important to remember that you should strive to keep the ignition coil secondary circuit (plug wire, plug cap, and spark plug) total resistance as close as possible to original specifications, which are:
    - 15K ohms per cylinder on all 1986 XJ700-X, XJ750-X, and XJ900 S/SH models.
    - 10K ohms per cylinder on all XJ550, 1985 XJ700-X models, 1986 XJ700 non-X, XJ750RL, and XJ900 N/FN and F models.
    - 5K ohms per cylinder on all XJ650, 1985 XJ700 non-X, all 1981-83 XJ750 models, XJ750-D, XJ900RK and RL models, and XJ1100 models. Although some manuals may call for a different resistor rating on inner vs. outer caps, we've never seen such a combination on an actual bike

    So with that information the published information in the FSM must be incorrect?
     
    Rooster53, Oct 15, 2014
    #5
  6. k-moe

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

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    Typos happen all the time, and are almost never corrected in service manuals.
     
    k-moe, Oct 15, 2014
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  7. Polock

    Polock Well-Known Member

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    Polock, Oct 15, 2014
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  8. k-moe

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

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    Less resistance also changes spark duration. Less resistance is not always better. The cumbustion chamber shape, valve overlap, and compression ratio were all developed based on a specific spark voltage and duration.
     
    k-moe, Oct 15, 2014
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  9. Polock

    Polock Well-Known Member

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    i think we have to agree to disagree, and that's ok
     
    Polock, Oct 15, 2014
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    k-moe likes this.
  10. k-moe

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

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    I'm not saying that it won't work. I'm just saying that it might not be ideal for every riding situation.
     
    k-moe, Oct 15, 2014
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