1970 RS Z28. Running a factory LT1

Discussion in 'Troubleshooting & Diagnosis' started by harkz28, Nov 19, 2017.

  1. harkz28

    harkz28 New Member

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    Aug 22, 2005
    1970 Z28 LT1 Stock Holley 780 MSD ignition. When running at 70 on the freeway feels like the car is surging. Car seems to run fine on side streets at normal speeds. Any ideas?
     
  2. COPO

    COPO Veteran Member Lifetime Gold Member

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    Ontario, Canada
    Don't gap the plugs wider than .040 with MSD on a 70 LT1. Ask me how I know.
     
  3. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

    I'll bite. How do you know?
     
  4. COPO

    COPO Veteran Member Lifetime Gold Member

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    Cause I tried .045, .040 and .035 with my MSD 6420 and .045 gave me a hesitation above 2500 rpm and up cruise and even a gradual increase in rpm from a dead stop.
     
  5. SRGN

    SRGN Veteran Member

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    Feb 20, 2009
    Central NJ
    Without a wideband to verify air fuel ratios, you can't be 100% positive it was the ignition system alone. Lean mixtures are notoriously difficult to ignite.
     
  6. COPO

    COPO Veteran Member Lifetime Gold Member

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    Ontario, Canada
    Get the highest vacuum reading on your idle mixture screws too. Not everyone has a W/B, that makes it too easy. I don’t and won't drill a hole for one. We never had them in the 60’s and early 70’s when HP was at it’s peak on leaded Sunoco 260 fuel and we got by.
     
    Last edited: Nov 19, 2017
  7. SRGN

    SRGN Veteran Member

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    Central NJ
    You don't need a hole, they make a tailpipe clamp if you were so inclined to use one. Technology has advanced considerably since 10mpg, 250hp cars were built. I choose to embrace it and reap the benefits.
     
  8. COPO

    COPO Veteran Member Lifetime Gold Member

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    IMO, the tailpipe is too far away for an accurate reading.
     
  9. 70lt1z28

    70lt1z28 Veteran Member Gold Member

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    Oct 3, 1999
    Beavercreek, Ohio, USA
    For something like the stock exhaust on a 70, I would not be afraid of taking an old heat riser and moding it for the sensor. Bolt it in, take readings and adjust and them put the original back in. Yeah, its a bit of work, but what isn't.
     
  10. COPO

    COPO Veteran Member Lifetime Gold Member

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    I would leave the moded heat riser in place.
     

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