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Need some help, fowling plugs

Discussion in 'XJ Technical Chat' started by JBurch, Aug 9, 2021.

  1. JBurch

    JBurch Active Member

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    I'll admit right up front, I suck at trouble shooting

    Bike just developed a miss fire, at steady throttle, on cylinders 1 and 3, plugs sooty black. Checked coils; 1 & 4 primary ohms out at 2.6 ohms, secondary 20.93 K ohms; 2 & 3 primary ohms out at 2.6 ohms, secondary ohms out at 29.75 K ohms.

    I will have a fresh set of plugs tomorrow, NAPA had to order them in.

    Another thought is that it is carburetor related, not looking forward to pulling carbs off if I don't have to.

    Looking for ideas.
    Thanks,
    Jim
     
  2. Blackbird

    Blackbird Member

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  3. XJ550H

    XJ550H Well-Known Member Premium Member

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    Ignition Coils: 650 specs as you did not say which bike

    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

    you do have a coil out of spec coil pack for 2 and 3. 29k is high

    but your issue is with cylinders 1 and 3 not connected to same coil

    ohm out the caps make sure you have non resistor plugs trim all plug wires back a little incase they have corroded.
    swap plug wire i with 4 see if issue follows plug wire do the same fr other coil
     
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  4. JBurch

    JBurch Active Member

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    Thanks, I'll check it out tomorrow. Sorry I should have said my bike is 650 Seca
     
  5. JBurch

    JBurch Active Member

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    Yesterday I went out and went back over my coils, caps and plugs; here is what I got:
    #1 plug cap: 4.32Kohms
    #2 plug cap: 8.53 Kohms
    #3 plug cap: 9.18 Kohms
    #4 plug cap: 4.62 Kohms


    Coil 1 & 4 secondary ohms: 11.83 Kohms
    Coil 2 & 3 secondary ohms: 11.71Kohms

    My coil readings in my first post was done with plugs caps on, FSM (not Haynes) did not say to remove caps

    Swapped leads to cylinders 1 & 4, and leads to cylinders 2 & 3

    Coils, caps, plugs are how I received the bike, plugs looked good I saw no urgent need to swap them out; did not have knowledge issues of nonresistor plugs/resistor caps, resister plugs/nonresister caps

    Tried to purchase set of BP7ES plugs from NAPA; can't get them, ended up with resister plugs, put them in for short blast, #1 still very sooty, 2, 3, and 4 not so much.

    Gonna order up a set of nonresister caps from Len

    I'll keep poking
     
  6. XJ550H

    XJ550H Well-Known Member Premium Member

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    you need to get 5 k caps for the 2 and 3 cylinder.
    it is ok to measure plug wires with caps in place just remember to add the value to the specs . you would remove the caps if total was out of spec to find the offending part
    our supporting vendor has BP7ES he has stated ngk is subing in the resistive plugs and phasing out non resistor plugs.
    you can get 0 ohm caps( at this point called boots) and use resistor plugs up side is you refreash the resitor when you install new plugs and no longer have to worry about the cap resistance
     
  7. JBurch

    JBurch Active Member

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    Update: Swapped wires around to see if plug fowling moved with wires: no. Next I ordered up new plugs and caps from Len, installed new non resister caps and resister plugs, went for 20 mile ride, 1 and 3 plugs fowled dry black soot. Took carbs off, didn't want to but figured at this point issue was carb/fuel related. Carefully cleaned each carb, reassembled, put them back on the bike. Then the starter gave up, order kit from Len, rebuild starter, wait for fair weather, went on 20 mile ride, now only cylinder 1 is fowling, took rack off again, clean #1 again, reassemble, waiting to go for ride. As a side note, color tune shows #1 nice blue flame. I will let you know results of next ride.

    Any other ideas, things to check, let me know.
    Thanks,
    Jim
     
  8. XJ550H

    XJ550H Well-Known Member Premium Member

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    main jet and pilot jet being reversed will cause fouling
    same with air jets
     
  9. JBurch

    JBurch Active Member

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    How did they get swapped to begin with? I have about 1500 to 1800 miles on this rack after a Hogfiddles rebuild with zero problems until now.

    Going out now for a shake down ride to see if I corrected the problem, more news later.
     
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