ignition timing BBC
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ignition timing BBC

  1. #1
    Senior Member 69 wriedt devil's Avatar
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    Default ignition timing BBC

    was wondering if someone can steer me in the right direction. I have a blown BBc 427 with 2 750 holley carbs. the boat runs great for the most part. Now every now and again when i jump on the throttle, there is a nano second of a hesitation. fuel pressure set at 7. what should my timing be ballpark? since ive had the boat, never checked timing because the boat ran so good. thx

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    Senior Member 69 wriedt devil's Avatar
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    oh yeah, i removed my headers and installed zoomies. didnt like the zoomies so i re-installed headers, not sure if that makes a difference.

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    Or Seth, either one Budweiser's Avatar
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    The guys who will be able to help will want to know your compression ratio, how much boost you're making, and what fuel you use. Might also want to know aluminum or iron cylinder heads, distributor, and if it's locked.
    Last edited by Budweiser; 07-06-2012 at 08:18 AM.

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    Senior Member 69 wriedt devil's Avatar
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    great, dont have a boost guage, not sure about compression, thats what sucks when you buy an engine and the guy you bought it from doesnt know anything. i am running 100LL av gas, and mallory distributor with pertronix no points. thx

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    Senior Member 69 wriedt devil's Avatar
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    All the info i have

    Mfi
    Locked distributor
    Iron heads
    Twin 750 holleys.
    100ll av gas
    Gonna buy a boost guage, but will not know compression ratio
    Idles at 1100

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    Or Seth, either one Budweiser's Avatar
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    What is your timing set at now?

    I have next to zero experience with blower engines, so I'm not the guy to send you in the right direction... just making it easier to get the answer you're after.

    In my experience, a slight hesitation off idle would be a carb setting issue. Accelerator pump, accelerator pump cam, transition circuit... something like that. But, who knows...

    Oh! What blower? 8-71??? Over/under drive ratio?

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    The first place I have always been told to look was the accelerator pump

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    Senior Member 69 wriedt devil's Avatar
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    Ok. Thanks and thanks. I need to provide more info. Will check timing and accelerator pumps as well. Also its 6-71 bds and underdriven, but not sure how much. Thanks and i will play with it tomorrow.

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    Senior Member wagspe208's Avatar
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    Look at overdrive/ underdrive. That will be a start.
    28 to 32 is a starting place.
    Hesitation with a locked advance is not a timing issue. It is a squirter or air bleed issue.
    If you ease into throttle does it hesitate, or if you whack it? The throttle...
    Wags

    BTW, with all the info you have you are going to get generalizations.

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    Senior Member wagspe208's Avatar
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    OH... 6-71 and underdriven... it ain't making much boost.
    If you take off the belt, does the blower turn easily by hand, or takes some effort?
    Wags

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    gn7
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    Quote Originally Posted by 69 wriedt flattie View Post
    All the info i have

    Mfi

    Locked distributor
    Iron heads
    Twin 750 holleys.
    100ll av gas
    Gonna buy a boost guage, but will not know compression ratio
    Idles at 1100
    OK, I'm confused

    Screw the compression or the boost. Is the hesitation form a part throttle stab, or flat footed from an idle?
    Are these double dumper 750s? Or Vac secondary?



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    Last edited by gn7; 07-06-2012 at 07:55 PM.

  14. #12
    Senior Member 69 wriedt devil's Avatar
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    ok from idle it responds well, if im moving good and stab the throttle, it has a real miniscule lag, then launches. my friend also suggested the squirters. so all of your advise is great.

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    Senior Member 69 wriedt devil's Avatar
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    sorry, they are both double dumpers.

  16. #14
    Senior Member 69 wriedt devil's Avatar
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    @wags turns with little effort

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