327 Backfire Under load?

Discussion in 'Troubleshooting & Diagnosis' started by '71StreetZ, Aug 18, 2017.

  1. '71StreetZ

    '71StreetZ New Member

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    Aug 18, 2017
    IMG_4430.JPG IMG_4431.JPG IMG_4430.JPG Hello, being a recent Member I figured I'd ask y'all if you knew anything about my problem, My 71 Camaro has a 327 Chevy in it that's been bored to a 334 has a hot comp cam, heads, edelbrock rpm intake and new carb but at about 4000 rpm under load it starts to hesitate then backfires I believe it's Ignition but don't know if it's just plugs or coil and needed some direction
     
  2. Gary S

    Gary S Administrator Lifetime Gold Member

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    Apr 14, 1999
    Bismarck, North Dakota
    I think you are on the right track thinking ignition problems. The only time I encountered that issue was with a points ignition that had worn points. It wouldn't be impossible for an HEI to do the same thing.
     
  3. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

    Start simple. Verify the hei is getting full voltage with a voltmeter not a light, and the connector is good and solid. Inspect cap and rotor, and the dizzy under the rotor to make sure everything moves good, no rust, no wear. Whats the base timing at? Running vac advance? Has it run well before with this distributor?
     
  4. '71StreetZ

    '71StreetZ New Member

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    Aug 18, 2017
    Base timing is at 14* BTDC and total is about 35 it has run well before but I've been fighting it burning up wires on the headers for some time so it's hard to say, no Vac advance just mechanical
     
  5. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

    Why no vac advance? Paging Damon....lol

    Double check voltage to it. A 71 i believe stock would had a ballast resistor and less than full voltage.
     
  6. cadillac_al

    cadillac_al Veteran Member

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    Apr 22, 2015
    Maine
    When I hear "backfire under load", my first thought is firing order messed up. If that is correct then something else is wrong with the ignition. Those burnt wires could be acting up.
     
  7. budro6968

    budro6968 Veteran Member

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    Apr 2, 2016
    Jax Florida
    I used to go to the junk yard and get a bunch of HEI wires to replace the burned ones. It was a constant thing. Header wrap would have worked but that had a hard time staying put.
     
  8. Dave Nelson

    Dave Nelson Veteran Member Gold Member

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    Dec 19, 2003
    Vineland N.J USA
    Burnt wires will do exactly what you describe. You need to make sure there is a decent airspace between the wires and headers. Start the car when it's dark out and look for arcing from wires, give it some throttle while checking, also listen for any ticking from arcing.
     
  9. Bandit723

    Bandit723 Veteran Member

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    Oct 1, 2016
    Waupaca WI
    So when does the backfire occur 1/4 throttle half throttle?
     
  10. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

    Misting a little water from a spray bottle helps with that
     

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