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  1. #1
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    Default 350 holley flat spot

    Hey guys I have a VJ valiant with a stock 245 hemi with extractors and a 350 holley, the carby has been rebuilt and has a new throttle plate assembly, also new manifold gasket, adjusted the bowl level, accel pump and throttle blades.

    My problem is I have a flat spot/hesitation off idle, I have a standard 4 speed with 2.92 LSD diff, the holley has a white accelerater pump cam on position 1, 35 or 36 squirt nozzle if I remember correctly

    Edit: has 31 nozzle

    Any help will be appreciated!
    Last edited by ETUQHNEDLOH2791; 29-05-2019 at 02:18 PM.

  2. #2
    Not the Kingswood! hq308's Avatar
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    When it hesitates is it rich or is it lean?

  3. #3
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    Hesitation is nearly always lean.

    Manual car really makes this stand out, but also makes it easier to know when and where and what you are trying solve.

    Have you got the Acc Pump arm adjust properly, no clearance at rest, and the clearance measured at wide open throttle? Have seen people get this back to front and cause the trouble you describe.

    A small hesitation might just need the mixtures taken out a 1/8 or 1/4 turn (made richer) be careful as some less common carbs have the mixtures back to front, as in, in for rich out for lean.

  4. #4
    Do you ever leave? EH179's Avatar
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    As per Mick's post above and check you don't have too much t/slot exposed.

    May need to spend time on the accel pump cam and squirters.

  5. #5
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    Try raising the float level 1/8". If that helps or fixes the problem, then it needs richening. A 35/36 squirter is already pretty large. Does the carb still have the power valve? What is the PV rating & what is the idle vacuum? Engine standard?

    Is the hesitation under very light throttle, heavy throttle or doesn't matter, it is always there.

  6. #6
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    Hesitation is always there, engine is stock pulling 22 inches of mercury, carb has a 6.5pv

  7. #7
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    HI
    PV needs to be half of idle vacuum
    Car currently is poorly setup P/V not opening till late
    Then Main jets are then expected to run rich to cover for the pv not really working much



    Start by setting up main jets for 80-90km light throttle cruise around 14 to 15:1 Airfuel ratio
    Under normal driving pv comes in after main jet . and under hard acceleration
    run the idle a bit rich
    the idle feed restrictor might need drilling to richen up off idle acceleration

    tune the accel pump squirter and cam
    check accel pump linkage adjustment


    Good engine condition already assumed
    vacuum leaks
    compressions
    ignition system
    cam is in good order
    fuel quality and fuel pump ok?
    carby float level and fuel pressure

  8. #8
    Not the Kingswood! hq308's Avatar
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    PV is certainly low for that much vacuum but IMHO not likely the issue (may be part of it though) as the hesitation is always there and PV only comes into play on the mains.

    It could well be a combination of issues, as GTO pointed out above 35/36 squirter seems a little on the large side and may be an attempt to bandaid the poor PV selection.

  9. #9
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    HI
    PV only works on really high percent of throttle/load eg very low vacuum . A little more than normal accel from traffic lights to 80km/h ,probably lean out . Power Valve Restrictors then need jetting for the top half of rev range as there are no secondaries

    The accel pump the cam does the volume . The squirter nozzle just times it eg all at once-- quick large initial spray or long and drawn out.

  10. #10
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    ETU,
    Need to know more about the hesitation. Is at light throttle taking off from a start? This might indicate the IFR needs to be enlarged.

    Is it when you are cruising & go to WOT? That would indicate a problem with the main system: PV rating, PVCR too small, float level etc.

    You need to be more specific.

  11. #11
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    The hesitation occurs off idle or at the start, doesn't matter if it it half throttle or full throttle, it'll still hesitate

    But when we took it out and it was already rolling, example 50-60kmh, then there wasn't a problemwith hesitation, only when idling in hear or from a stop does it happen

  12. #12
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    Holley States that if it is over 15 inches then the PV doesn't need to be half.

    No vacuum leaks, that is why we got a new gasket, rebuild kit and a new throttle assembly as the other was worn and caused a leak.

  13. #13
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    Do you have any other accelerator cams mate? The white one will be too small me thinks, try a blue one on
    position two and take it from there.

  14. #14
    Not the Kingswood! hq308's Avatar
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    The PV doesn't necessarily need to be half (that's old school thinking) but with that much vacuum it needs to be higher. My father in law has a mild 265 in his VJ Charger it has a 650 vac with a 10.5 PV and it runs mint. He had previously had a mild hesitation running an 8.5. From memory his engine has ~ 18" at idle (it's a manual too)

    Try a higher numbered PV, I think it will go a long way to getting you where you need to be.

    EDIT I think it will need some accel pump tuning as well

  15. #15
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    HI
    That's Holleys 3rd rule
    50% idle vacuum
    idle vacuum less 2 inches
    Then your 15 inch rule !!!!

    PV is for moderate to heavy load
    Typically check vacuum at light throttle cruise 60-80 kmh
    Operation start to occur after 80kmh vacuum reading
    Then drill out PV restrictors to richen at full load close to max rpm around 13:1 air fuel ratio

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