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Thread: throttle lag 3K to 4K rpm 72 MFI

  1. 08-15-2020, 01:58 PM #1
    72t4tom
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    throttle lag 3K to 4K rpm 72 MFI

    I am not sure if lag is the correct word, but as I am accelerating, as soon as I reach 3000 rpm, the engine falls flat until I pass 4000 than it picks up nicely and away we go.

    It is a stock 72 911 T with MFI. new injectors and rebuilt MFI pump & fuel pump, new plugs & wires

    It has the original distributor with only cap, rotor and oil wick being oiled

    any ideas as to where I should look next?
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  2. 08-15-2020, 02:28 PM #2
    bob joyce
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    there are people on this forum with much more knowledge and experience than me... 30 years ago i had this problem, The mechanic who worked for red mcclintoch in Berkley, and was incredibly good said that this problem normally, was do to , the intake stacks and butter fly's and linkage .
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  3. 08-15-2020, 05:15 PM #3
    NorthernThrux
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    Was the right space cam used when the MFI pump was rebuilt? S space cams in 72 and 73 had a noticable flat spot (lean) in that range, likely for emissions reasons. If everything is new and you know your vacuum advance is working properly, you really need an air-fuel-ratio meter to know what’s going on.
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  4. 08-15-2020, 06:04 PM #4
    bob joyce
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    yep ... that's how red fixed mine ... one of those big air thingys and linkage adjustment ...
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  5. 08-15-2020, 11:22 PM #5
    MattB
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    Ignition advance working OK?
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  6. 08-16-2020, 10:26 AM #6
    frederik
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    It could be anything. You need to go through CMA from start to finish:
    http://early911nzdownloads.yolasite....ure_adjust.pdf
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  7. 08-16-2020, 08:46 PM #7
    edmayo
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    Normally a rebuilt MFI pump will need some adjustment after installation. Was this a shop install or self done? Were any linkage rod adjustments made?
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  8. 08-19-2020, 05:09 AM #8
    BURN-BROS
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    If the pump was calibrated back to factory specs and you are running fuel with 10% ethanol, you will require about a 8% increase in fuel output.
    Aaron Burnham
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  9. 08-19-2020, 05:02 PM #9
    72targa
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    Quote Originally Posted by BURN-BROS View Post
    If the pump was calibrated back to factory specs and you are running fuel with 10% ethanol, you will require about a 8% increase in fuel output.
    Interesting to learn.
    Peter Kane

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  10. 08-20-2020, 04:26 AM #10
    BURN-BROS
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    If the throttle bodies were rebuilt, they were most likely had the bores cleaned up and larger throttle plates installed. This can affect part load and cruise so adjustment may need to be done in those areas.
    Aaron Burnham
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