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What causes backfiring??

Discussion in 'The Garage' started by CaveBlazin, Jan 14, 2004.

  1. CaveBlazin

    CaveBlazin 1/2 ton status Premium Member

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    My buddy has a 400sbc and he just had someone put a new carb on it and now its backfiring as he shuts it off. It will knock when he gets on the pedal a little. This just started after the carb change. Im sure its something easy (I HOPE!!) so what do I tell him other than take it back to the garage that put the carb on..
    Thanks,
    Spence
     
  2. clubba68

    clubba68 1/2 ton status

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    Check the timing on it.
     
  3. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    Could be wrong jets. 400's need bigger jets than a 350.
     
  4. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    Check the timing on it.

    [/ QUOTE ]

    2nd that.

    Check the firing order.

    Make sure the idle mixture is correct.

    Slow the idle down.
     
  5. thezentree

    thezentree 3/4 ton status

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    he asked what backfiring is, and even if yall cut to the chase and fixed his problem, i'm still curious. my understanding of it is, its when the exhaust gas is still combusting as it goes out the exhaust port. am i correct?
     
  6. great scott

    great scott 1/2 ton status

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    yeah is it poping up through the carb or out the tail pipe.
     
  7. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    It blows the power vlaves out of a holley carb when it happens too.
     
  8. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Backfiring is caused by combustion happening when the valves are open.
     
  9. supersize75

    supersize75 1/2 ton status

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    [ QUOTE ]
    It blows the power vlaves out of a holley carb when it happens too.

    [/ QUOTE ]

    haha now ya tell me, needless to say I just replaced that /forums/images/graemlins/tongue.gif
     
  10. R72K5

    R72K5 Banned

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    advanced too far, retard it a little and also get vacuum guage and make sure idle manifold vacuum is within 18 to 22, if not then adjust timing more until it is within that range
     
  11. CaveBlazin

    CaveBlazin 1/2 ton status Premium Member

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    Dang timing sounds about right cant believe I forgot that...
     

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