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Weak spark on 1 and 3 XJ650

Discussion in 'XJ Technical Chat' started by Thomas Dermako, Nov 23, 2019.

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  1. Thomas Dermako

    Thomas Dermako New Member

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    Hi all. Firstpost here. I just got an 82 650 that had been in dry heated storage for about 5 years. It ran when parked. The bike is generally very good shape. but only runs well on cylinders 2 and 4. Things I've tried include fresh gas new plugs cleaned and tighten caps,snip last quarter inch off plug end of high tension wire. Have verified that carbs are delivering fuel to all four cylinders. Pipes for two and four come up to operating temperature, 1 and 3 are barely warm. There is a weak spark on 1and3. Figured I'd ask you folks before I dive down the rabbit hole .
     
  2. Thomas Dermako

    Thomas Dermako New Member

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    Ps I have the cylinders numbered correctly left to right when seated
     
  3. XJ550H

    XJ550H Well-Known Member Premium Member

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    cylinders 1 and 4 run off of the same coil
    cylinders 2 and 3 run off of the other coil
    it is a weak spark to start with.
    my first guess would be the spark plug caps they unscrew from the plug wires swap them out trim a little off of the end not working and ohm them when off see if problem follows plug cap.

    swap the spark plugs next again see if the problem follows the plug.

    carb cleaning may be needed to resolve the issue
     
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  4. tabaka45

    tabaka45 Well-Known Member

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    I agree with XJ550, it's probably not the coils since you have one cylinder running well off of each coil. I assume that you determined there is a "weak spark" by observation and comparison. If so, then it has to be in the wire, plug or cap. Like XJ550 suggested, switch the plugs on the coil for 1 and 4 and see if you still get a weak spark on four. If so, you have a spark plug problem, if not, it's probably the cap or wire, or cap and wire connection. Repeat the same thing for the other coil.
     
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  5. Thomas Dermako

    Thomas Dermako New Member

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  6. Thomas Dermako

    Thomas Dermako New Member

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    Agree with your assessment I have installed new plugs and there's no change. I have new MGK caps on order they should be here tomorrow. In the meantime I'm going to get home readings on the existing caps and post my findings.
     
  7. XJ550H

    XJ550H Well-Known Member Premium Member

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    plug caps should be 5k ohms +- 20 percent
     
  8. Thomas Dermako

    Thomas Dermako New Member

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    Readings are 1-4: 8.99k, 5.70k, 7.20k, 8.11k. So they're way out of spec. What should the readings from the secondaries be?
     
  9. XJ550H

    XJ550H Well-Known Member Premium Member

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    11k end to end of sparkplug wire.

    looks like you only have 1 cap in spec

    old thread that has come up

    testing coils

    specs from that thread
    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
     
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  10. Thomas Dermako

    Thomas Dermako New Member

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    Changed all plug caps and properly rebuilt carbs. Much better~thanks folks.
     
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