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Thread: 68S - how rich / lean should the fuel air mix be?

  1. #11
    Are you using the factory prescribed jetting for the 68 S?
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  2. #12
    Senior Member
    Join Date
    Jul 2012
    Location
    Kent, UK
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    183
    Honestly, I don’t know.

    I had thought the poor power transition at lower revs was the ‘s’ cam, but the dyno guys suggest the carbs are over fuelling at low revs, which I was hoping I could adjust will idle mix or air adjustment screw.
    Rich
    68 911S
    mbr. 2393

  3. #13
    Senior Member
    Join Date
    Jul 2012
    Location
    Kent, UK
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    183
    Opened up the carb today to reveal ‘factory’ jetting 55 idle 125 mains 185 air correction jet.

    Have a theory why the dyno sheet presents as over fueling, that on the dyno test the tester has applied full throttle at 3000 rpm which is off the cam sweet spot and it flooded the engine.

    Thoughts?
    Rich
    68 911S
    mbr. 2393

  4. #14
    Senior Member frederik's Avatar
    Join Date
    Sep 2018
    Location
    Netherlands
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    299
    Maybe it would work better to drive around with a wideband AFR sensor in the exhaust, with someone next to you taking notes of the AFR with different throttle / RPM combinations? That's what we did with my engine. I believe you want to optimize for drivability, so mid-RPM, half-throttle usage, and then verify that you're getting a decent AFR on full throttle from mid- to top RPM.
    1972 911 2.4T Targa Aubergine (MFI)
    2000 996 Carrera Ocean Blue
    Member #3833

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