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sputter/misfire

Discussion in 'Technical Q&A' started by 91.5mm Buick, Sep 1, 2010.

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  1. 91.5mm Buick

    91.5mm Buick Rookie

    Mar 5, 2008
    7
    ma
    #1 91.5mm Buick, Sep 1, 2010
    Hello everyone.My name is Tony and I`m helping someone with a 71 daytona.It`s a v12,Twin dist,and has 6 carbsThe car has the dist upgrade to electronic.
    Here is the problem.The car cold is runs great,idles and part throttle and accell.With the car warm we get a off idle stumble(flat spot) but 1/2 pedal and accell is okay.With car fully hot it is a bear to drive.Just getting off the stoplite is rough.Seems like the transition jets are not working.if you goin like 30-40 mph in 2nd gear just off idle accell it starts to jerk around till you hit the accell pedal past that point.
    Things we have done is inspect the cap and rotor for cracks and carbon trail.None found.Pulled tops off carbs and checked for sludge and dirt.Found some stuff at the bottom of the bowl so we disasembled all the carbs one by one.Pulled all the jets and used carb cleaner and sea foam to trace the channels of carb then blew carb out with compressed air.We reset the floats.Reinstalled carbs and road tested car.Its the same thing.seems like better top end performance but still has the low end stumble/misfire.We also installed new plugs.
    Just looking for direction on where to go.
    Tony
     
  2. bill.jones

    bill.jones Karting

    May 29, 2009
    64
    Adelaide, Australia
    Full Name:
    Bill Jones
    #2 bill.jones, Sep 2, 2010
    Possible fuel starvation??? Is there a petrol tank filter??? In-line filter??? Check for fuel flow rate. Good luck.
     
  3. PV Dirk

    PV Dirk F1 Veteran

    Jul 26, 2009
    5,401
    Ahwatukee, AZ
    #3 PV Dirk, Sep 3, 2010
    My first thought was vaccuum leak, which would lead to the fuel starvation listed above. Keep us up to date on how things go.
     
  4. Ferraripilot

    Ferraripilot F1 World Champ
    Owner Project Master

    May 10, 2006
    17,923
    Atlanta
    Full Name:
    John!
    #4 Ferraripilot, Sep 3, 2010
    run a compression check while cold and then while hot. See what's changing. May be something that's opening up once the engine is hot.
     
  5. brian.s

    brian.s F1 Rookie
    Professional Ferrari Technician

    Nov 3, 2003
    3,809
    Midwest
    Full Name:
    Brian
    #5 brian.s, Sep 4, 2010
    Always start with the basics, ignition first. Timing, advance curves, wires, plugs should be correct.

    Then search here for Weber tutorials, very important to syncronise and set basic idle mixture.
     
  6. 91.5mm Buick

    91.5mm Buick Rookie

    Mar 5, 2008
    7
    ma
    #6 91.5mm Buick, Sep 7, 2010
    Today we checked to see if the correct carbs were on it.
    They are 40 DCN 21/A
    The main jets are 140`s
    The idle jets on the side are 60`s
    The air bleed jets are 190
    The emultion tubes are F25
    Does anyone know if these jets are the correct ones for a usa spec car.This car came from over seas and i`m wondering maybe it`s jetted for their fuel and not usa fuel.
    We put new plugs in it with new wire set.This car runs perfect when you when your into the gas pedal.But when you cruising along at low speed barely touching the gas it bucks and pops.Seems to be the transition jet in the carb.

    Tony
     

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