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Thread: dmaddox's 1968 911L workshop

  1. #31
    Senior Member
    Join Date
    Sep 2020
    Long Island, NY
    Update - Idle and popping.

    A special thank you again to @edmayo and @1quicks for the fantastic documentation (and hefty load of patience). I owe you guys - and I hope you don't mind me posting the high level process in setting up and dialing in my particular Webers (40IDAP3C1's).

    What is important is the initial setup.

    Assumed: Valve lash set, timing set at initial timing settings, fuel filters/pump and pressure set, spark/ignition in good working order and carbs maintained/rebuilt and in good working order.

    Here is what worked for me - and it was an amazing learning experience. Weather good, timing light in hand, along with a synchrometer and your favorite snubby flat screwdriver, get into a well ventilated area.

    First - setting up the carbs for initial tune - this will be the "zero". (along with a plug for my instagram account)

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    A) The idle stop/speed screw, just until touching the arm and then 3/4 of a turn.
    B) Idle mixture screw, carefully (do NOT snug them in) seat them and then dial them out 2 full turns.
    C) Idle air adjusting screws, loosen up the 8mm lock nut and lightly seat them all in.

    You're now zeroed in. (at least this is what I call it - keep in mind this time last year, I had never even seen a 40IDAP in person nor owned a Porsche of any kind.)

    I then warmed up the engine, let it idle for awhile - it still and probably wont idle optimally, but I used the hand throttle to keep it running until it warmed up. Once warm, I adjusted the stop screws (A) to get the motor to idle right at 1000 rpm (even if its bobbling around in the 980 to 1150 range.

    Once warm, I made sure the hand throttle was all the way down and I disconnected the drop links to the throttle cross-arm.

    Now the first round of testing on the idle mixture (B) screws. I had 5-gallon bucket I sat on, was about the perfect height to sit on and fiddle with these. THIS is fun. Starting at #1, I turn the screws in 1/4 turn, waiting a few seconds between each turn until the motor said "cough, need....fuel..." on that cylinder. You'll feel/hear it. Then, back the screw out until it smooths out. Repeat for each cylinder. Recheck timing and idle speed. Should still be the same.

    Now, pop the synchrometer on top of #1:

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    With a notepad/pen - jot down where each cylinder reads, and then on the first bank, note the highest of the readings. Mine was cylinder #3, at 4, right on the money.

    So, I then backed out cylinders 1 & 2 to match #3, so that all three in the bank read 4. Lock down the 8mm's.

    Repeat for 4,5, and 6 so that all in the 2nd bank are at the same, lock those down too so that all are drawing the same air.

    At this point, I zeroed the idle stops again so they were both 3/4 turn in past touching. Doing so, I was right at 900:

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    Turning in the idle stops screws at the exact same amount on both banks to achieve 1000 rpm is next (1000 rpm it is easier to hear/feel the drops in rpm when you are lean dropping).

    I now repeat the "quick adjust" on each cylinder's idle mix screw (B), once more. This is turn in 1/4 turn, wait a few sec, turn in again, wait a few seconds until the cylinder stumbles. Back it out to smooth the idle, repeat for the other cylinders. When done, adjust to 1000rpm again, verify timing.

    Now, I carefully and slowly went through the process again, I know this will sound cheesy, but I literally had my eyes closed, turning the #1 cylinder idle mix screw in little by little, waiting between each 1/8th turn listening for even the slightest interruption of idle. When that moment came, I backed it out 1/2 turn. I repeated then for each of the other cylinders. I knew immediately when even getting to cylinder #3 that the sound was magic and the bumbling/popping and hesitation was gone.

    I took the car for a spin and I kept thinking THIS is what is supposed to be like.....flying down the back roads of Great Neck, NY....slamming through the gears, wow. During the drive I did note a very slight pop up through the carbs when I would "blip" the throttle, so on the side of the road, I opened up each mixture screw another 1/8th turn and pretended to be McQueen on the opening of LeMans when he pulled over his 911S to gaze around. Then, I hopped back in and continued the testing and found all popping/sniffing was gone and the blips, power and throttle response were amazing.

    What an experience. Again, this may sound cheesy or line out of a book, but I couldn't help but think of all the work we all do on our cars, we save, we trade, we buy things from each other all in hopes that we can experience what I felt undeserving to experience. So much fun.

    Now, onto fix the next thing. Maybe I can start my own show called "The Next Fix Thing" ha!

    Cheers - dallas
    Looking for motor number: 3280343 (I am running engine number 3280124)
    Looking for transmission number: 3280571

    My 78 FJ40 Build

  2. #32
    Well,,, you are a quick learner,,,,and nice write up. As you can see just because some one says "oh I've done the carburetors" doesn't necessarily mean they were done right. as you found out. The giveaway is when the poster says "I've got all the idle mixture screws 3 (or whatever) turns out. As you just experienced, the engine will tell you how many turns out each will be. Glad you got it right and have now experienced the difference.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

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