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Won't start but backfires VERY Bad

Discussion in 'XJ Technical Chat' started by Bjarvis, Aug 30, 2012.

  1. Bjarvis

    Bjarvis Member

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    So I took the carbs off and cleaned them all out - tried to sync the carbs but everything way out - took carbs off again and checked everything over including float levels adjusted them to 3mm plus or minus 1mm. Set air mix screws at 21/4 turns. Put carbs back on - checked plugs fairly new and good shape ensured gap was .30 - tried starting no go but very loud backfire.

    Think I scared the neighbors - waiting for the police to come by - thinking what to try next ........

    Could this be a float issue ??? Could it be too much fuel in the floats.. I pulled the plugs their dry
     
    Bjarvis, Aug 30, 2012
    #1
  2. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    Ummm...

    Have you checked the VALVE CLEARANCES yet? Done a compression test?

    Are you running a modified intake or exhaust?


    [​IMG]
     
    bigfitz52, Aug 30, 2012
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  3. Bjarvis

    Bjarvis Member

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    No I haven't checked the valves - it was running last week started real good but was just rough, that is why a cleaned the carbs.

    Is there a valve adjustment guide for dummies ??
     
    Bjarvis, Aug 30, 2012
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  4. Bjarvis

    Bjarvis Member

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    Bjarvis, Aug 30, 2012
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  5. yamamann

    yamamann Member

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    compression test like bigfitz52 asked ?
     
    yamamann, Aug 30, 2012
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  6. Bjarvis

    Bjarvis Member

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    Yes, will do a compression test but need to get a tester first. Thanks
     
    Bjarvis, Aug 31, 2012
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  7. MiCarl

    MiCarl Active Member

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    Spark plug wires or coil wires switched?
     
    MiCarl, Aug 31, 2012
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  8. jeffcoslacker

    jeffcoslacker Member

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    Backfire through intake or exhaust?
     
    jeffcoslacker, Aug 31, 2012
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  9. moellear

    moellear Member

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    http://xjbikes.com/Forums/viewtopic/t=14827.html

    written by our good man, Fitz. just listen to and believe everything he says. he knows XJ stuff really well
     
    moellear, Aug 31, 2012
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  10. Bjarvis

    Bjarvis Member

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    Compression test done: All look good
    #1 150
    #2 155
    #3 160
    #4 158

    Took carbs off again and checked floats #3 seemed to be sticking so I took it off and adjusted it. Then bench set the carb sync again put carbs back on and secured with new clamps. Bike fired up and started but real rough - played with the sync using the 2 glass bootls with water as manometer eventually things started coming together .... Just went real slow ... Now running great. Will check it in the morning again and adjust air mixture.

    Seems I was perhaps confused with the carb sync screws and how they work..but once that became clear things went quick.

    Thanks for all the advice read a lot of past posts to finally get it running - was very time consuming but very interesting to work on...
     
    Bjarvis, Sep 1, 2012
    #10
  11. MN-Maxims

    MN-Maxims St. Paul Minnesota

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    Compression looks good. When you get time soon pull the valve cover and check your clearances. You can't really get a good sync untill you do.

    MN

    PS. Order a new gasket and and any other rubber goods for your valve cover before you start. xj4ever has them.
     
    MN-Maxims, Sep 1, 2012
    #11

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