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engine backfiring,please help

Discussion in 'The Garage' started by jones, Jan 11, 2007.

  1. jones

    jones 1/2 ton status

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    i really don't have the specs for this engine other than it's a recent rebuild.i was told it was a .030 over 350,but it actually turned out to be a 400.i haven't pulled the heads to be sure it's bored.it's backfiring through the exhaust and the carb.i haven't found any vacuum leaks,the headers are snug(no leaks there),i've advanced and retarded the timing via the distributor to no avail.it's got a stock type fuel pump,holley 650 double pumper,882 heads(u/k if they've been worked over.)i'm pulling my hair out trying to get it running right.pleeeeeeeeease help!thanks!
     
  2. 58 apache

    58 apache 1/2 ton status

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    sounds like timing... are you sure its right? it could be way off
     
  3. Avery4jc

    Avery4jc 1 ton status Premium Member GMOTM Winner

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    my truck has been having some small backfiring issues lately too...when does your's do it? Mine does it when I get into the throttle (in 1st) and when I let off a little it'll sort of pop...
     
  4. bigblock72

    bigblock72 1/2 ton status Premium Member GMOTM Winner

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    When is it back firing? if it pops out the intake under accleration than it's probably lean, if it pops both out of the exhaust and the intake simultaniously than you may have a valve problem, likely a broken valve spring. Valvetrain problems always cause the engine to run real rough especially at an idle and will cause it to backfire as the engine speed is raised or engine loaded down.
    Please post more specifics and I can help you more.
     
  5. AussieK5

    AussieK5 1/2 ton status

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    Choked plugs will also cause merry mayhem. A front mount PCV on a stock intake can (depending on engine age, rocker covers etc) can foul No 2 after sometime.

    What did your plugs tell you when you pulled them?
     
  6. jones

    jones 1/2 ton status

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    more specs:edelbrock intake,PCV into valve cover towards the back of the engine,pass.side.idles fairly smooth,starts popping through exhaust at op.temp,though not constantly.bleeping the throttle gets more exhaust popping,then a good pop through the carb.plugs are new as are the wires.plus not getting to hot or fouling(black sooty)they were wet with gas:eek1: ,hopefully not a bad thing.hope that helps,thanks!
     
  7. 58 apache

    58 apache 1/2 ton status

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    sounds like timing is 180 out
     
  8. bigblock72

    bigblock72 1/2 ton status Premium Member GMOTM Winner

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    Pop those valve covers off real quick and make sure no broken rockers or valve springs. Usually a valve spring will break the second coil down and may be hard to see. If the timing were 180 out it wouldn't start, you've replaced plugs and wires and moved the distributor all over with no change so that rules out spark issues, a carb wouldn't normally cause the backfiring problem. Time to move on to valvetrain.
     
  9. jones

    jones 1/2 ton status

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    thanks for all the suggestions,guys.it's very much appreciated.i'll make time this weekend to pull the covers.aside from checking the springs for cracks,should i check for any thing else?would it do the same thing if the rockers were to tight?how do i go about tuning aholley carb(650 double pump;model# u/k)?
     

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