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backfiring through exhaust manifold

Discussion in 'Technical Q&A' started by wildskinner, Jul 19, 2007.

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  1. wildskinner

    wildskinner Rookie

    Jul 19, 2007
    2
    #1 wildskinner, Jul 19, 2007
    Have a 308 which burnt its points out twice in two weeks. The idle speed is wrong (a bit Low) and the timing is 6btdc. When revved the 5-8 bank backfires through the exhaust manifold. The valve timing has been double checked as has the firing order on cap as well as engine. Can the carbs out of tune give this fault? Points and condensers changed twice aswell.
     
  2. BigTex

    BigTex Seven Time F1 World Champ
    Owner Rossa Subscribed

    Dec 6, 2002
    79,406
    Houston, Texas
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    Bubba
    #2 BigTex, Jul 19, 2007
    Hmmmm....welcome!

    Have you verified the distribs are advancing, with the revs????

    Both of them together, more or less?
     
  3. cavallo_nero

    cavallo_nero Formula 3

    Nov 3, 2003
    1,707
    colorado
    Full Name:
    Giovanni Pasquale
    #3 cavallo_nero, Jul 20, 2007
    my carby 308 does the same thing on one bank, it turns out i have a leaky intake manifold gasket - i will change it this winter, hence it backfires out the exhaust...
     
  4. Irishman

    Irishman F1 Rookie

    Oct 13, 2005
    3,526
    Raleigh
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    Kevin
    #4 Irishman, Jul 20, 2007
    This is good to know, thanks. I just replaced the intake manifold gaskets on my '89 Harley. Runs much better now. It generally ran like crap in cold conditions but no backfire. It must run leaner under these conditions. Made me wonder if it was a bad thing to be running it like that for any length of time.

    Seamus
     
  5. wildskinner

    wildskinner Rookie

    Jul 19, 2007
    2
    #5 wildskinner, Jul 21, 2007
    Sorry, forgot so say the backfire was at idle
     
  6. BillyD

    BillyD Formula 3
    Silver Subscribed

    Feb 28, 2004
    1,836
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    Bill
    #6 BillyD, Jul 21, 2007
    I'll bet u'll find a fouled plug that is letting unburnt gas into exhaust system & its igniting when it hits the hot exhaust from other cylinders.
    my .02
    Bill
     

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