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Spark plug boots

Discussion in 'XJ Technical Chat' started by bminis01, Mar 30, 2019.

  1. bminis01

    bminis01 New Member

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    OK, so I checked the ohms on my plug boots and got two at 6 and one at 5, and one that I can't get a response to. My bike is running on all 4 cylinders and I'm running non- resistor plugs. So my question is, is that boot bad or is it a non - resistor cap. I'm getting ready to start syncing the carbs, and checking things before I do. I'm thinking I should just get new boots for the wires. Thanks.
     
  2. Chitwood

    Chitwood Well-Known Member

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    Have you checked valve clearances? I would suspect that the plug cap is bad if you cant get a reading on it. They aren't that expensive to replace. Also look at the plug wire to make sure it's not corroded at all
     
  3. cgutz

    cgutz Well-Known Member

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    I had a plug boot that showed it wasn't passing current on an ohm meter.. Cylinder was firing, but it ran better after replacing. I suspect ignition had enough oomph to jump resistance in boot, but it had to be a weak spark.
     
  4. bminis01

    bminis01 New Member

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    Don't have the valve clearances with me but they are in spec. I should probably cut a little off the end of the wires too. Thanks.
     
  5. XJ550H

    XJ550H Well-Known Member Premium Member

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    if it is an oem cap you can use a flat blade screwdriver inside where the sparkplug goes to tighten up the screw.
    put the spark plug back into the cap and use the plug electrode as the contact point to measure the resistance.

    also with caps off measure from end to end of the spark plug wires for each ignition coil.


    and just FYI a sparkplug boot is just that a boot, no resistor . a spark plug cap has a resistor in it.
     
  6. XJ550H

    XJ550H Well-Known Member Premium Member

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    you have a xj650?
    specs

    Pick-up coils:
    1980-81 XJ650 Maxim and Midnight Maxim: 700 ohms +/- 20% = 560 ohms to 840 ohms acceptable range
    1982 XJ650RJ Seca (non-yics engines): 700 ohms +/- 20% = 560 ohms to 840 ohms acceptable range
    1982-84 XJ650 Maxim: 650 ohms +/- 20% = 520 ohms to 780 ohms acceptable range
    1982 XJ650RJC Seca (yics engine): 650 ohms +/- 20% = 520 ohms to 780 ohms acceptable range
    Ignition Coils:

    Primary side (input from main wiring harness):
    2.5 ohms +/- 10% = 2.25 ohms - 2.75 ohms acceptable range

    Secondary side (spark plug wires, without their end caps):
    11K ohms +/- 20% = 8,800 ohms - 13,200 ohms acceptable range

    Spark plug caps:
    5K +/- 20% = 4,000 to 6,000 ohms per cap acceptable range

    Spark plugs:
    0 ohms per plug
     
  7. Calvert

    Calvert New Member

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    Sorry to chime in a year later... Looking to replace the spark plug caps and possibly ignition coils. My Haynes manual states:

    Plug cap resistance
    UK Models
    Cylinders 1 and 4 (5 K ohm)
    Cylinders 2 and 3 (5 K ohm)
    US models
    Cylinders 1 and 4 (5 K ohm)
    Cylinders 2 and 3 (10 K ohm)

    Considering the spark plugs and ignition coil resistance are consistent across the models, is there any particular reason I should use a 5kohm vs a 10kohm on cylinders 2 and 3?

    I have a 1982 XJ650J Maxim (US model)
     
  8. XJ550H

    XJ550H Well-Known Member Premium Member

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    it is an error in the haynes manual


    specs are in this link
    The Ultimate Relay, Switch, Sensor, and Diodes Guide
    XJ650 models:

    Pick-up coils:
    1980-81 XJ650 Maxim and Midnight Maxim: 700 ohms +/- 20% = 560 ohms to 840 ohms acceptable range
    1982 XJ650RJ Seca (non-yics engines): 700 ohms +/- 20% = 560 ohms to 840 ohms acceptable range
    1982-84 XJ650 Maxim: 650 ohms +/- 20% = 520 ohms to 780 ohms acceptable range
    1982 XJ650RJC Seca (yics engine): 650 ohms +/- 20% = 520 ohms to 780 ohms acceptable range
    1982-83 XJ650 Turbo: 120 ohms +/- 20% = 96 ohms to 144 ohms acceptable range


    Ignition Coils:

    Primary side (input from main wiring harness):
    2.5 ohms +/- 10% = 2.25 ohms - 2.75 ohms acceptable range

    Secondary side (spark plug wires, without their end caps):
    11K ohms +/- 20% = 8,800 ohms - 13,200 ohms acceptable range


    Spark plug caps:
    5K +/- 20% = 4,000 to 6,000 ohms per cap acceptable range

    Spark plugs:
    0 ohms per plug
     
    Chitwood likes this.

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