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Thread: Solex Carb Tuning

  1. #1
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    Solex Carb Tuning

    Any ideas as to where one can find tuning data for Solex carbs? ('65 911) Carbs have been kitted, accelerator pumps adjusted, float levels set--new mechanical pumps and electrical supply pump. Balanced carbs with synchro---. with all adjustment needlevalves opened 2 turns. Engine runs very rich, tried to lean with needle valves without success. The only info I currently have is an old Haynes manual---limited in scope.
    My intent is to try to resolve this problem, then to store original carbs and replace with Webers. (Engine is 2 liter which I overhauled this winter) 911 had been stored for around 20 yrs, and, I believe , was running rich when I parked it... Any help would be very appreciated. Thanks, Steve L
    '65 911
    '02 M5
    '03 MCS

  2. #2
    Early 911S Registry # 237 NeunElf's Avatar
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    Well, there's some information in the factory shop manual. But, I followed it and my '65 with Solexes runs rich, too.

    An unusual part of the procedure is that you unhitch the right side and left side carbs, then crank the throttle on one side only to get the engine up to 1200 -1400 rpm synchronize the carbs, adjust mixture, bring it back to 900 rpm, recheck carb synchronization, adjust mixture, put the air cleaner back on...and yes adjust mixture agan.

    There isn't really a ton of detail--I guess in 1965 Porsche mechanics all just knew what to do with six carburetors.

    Good luck.

  3. #3
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    NuenElf, Thanks for the reply. May I ask what type of sparkplugs do you use? Also, can a person use multiple sparking on these early models in hopes of more complete ignition/less sparkplug fouling? Can one change the jets in the carbs? And finally, the adjusting needle valves look as though they are ported downstream of the throttle butterfly(negative press?), and appear to be internally ported to the jet module (nomenclature suspect), so as one tightens (clockwise) the needle valve, does this decrease the available air?? Clearly, I'm not really sure as the mechanics of this unit, certainly can't let that stop me. Thanks again. Steve
    '65 911
    '02 M5
    '03 MCS

  4. #4
    Early 911S Registry # 237 NeunElf's Avatar
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    According to the leftover boxes, I installed Bosch W5DC plugs last time.

    I wouldn't have any idea where you would get a multiple firing ignition system. I have degrees in electrical engineering, but two decades doing systems and software engineering on surveillance radar and spacecraft doesn't make me an ignition espert.

    It is extremely easy to change the jets in the Solex 40PI carbs: all the jets live in little jet carriers and you can get them out by removing two screws. You might be able to do that after only removing the air filter. Worst case, you'll need to take off the velocity stacks. But, I don't know where to get alternative jets.

    I think the "mixture screw" is officially called a "volume screw." It actually regulates an extremely rich fuel/air mix that comes through some of the jets. It is downstream of the throttle plate.

    As far as I know, screwing it in means less and screwing it out means more (essentially richer).

    One warning the factory shop manual gives, and I was also told by Matt Blast of Eurometrix: If a carb just won't cooperate, the problem may well be that the throttle plate is not in the correct position on its shaft. The throttle plate has to close absolutely completely (when you have the carb off the car--that doesn't mean you need to adjust the throttle stop all the way closed).

    Note that the throttle plates are bevelled on their edges and that bevel defines a top and a bottom surface. Put the plate in upside down and they'll never close.

  5. #5
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    E.E.---never could trust something I couldn't see Was running NGK 7's---after reading a number of posts, changed to a hotter plug (6 ES). Also discovered pitting on points, dressed and regapped to .014. I installed clear fuel feed line and a clear filter after overhaul (many yrs inactivity prior ) and am seeing what appears to be rust accumulating on filter membrane, Sooo- pulled float reservoirs (no debris) then pulled "jet packs" on a couple of carbs and found no debris--reassembled then fired her up after opening "mixing jets" 2 turns. Used synchronometer to balance 1 and 4, then remaining carbs at 1400 RPM--running rich so closed each of the adjusting screws until the cylinder "dropped out" then opened screw until cylinder "picked up" (around 1.25 turns). Read another post saying adjustments should be made in 1/8th increments(my adjustments were more on the order of .5 turns) Happy to say the majority of the exhaust smoke (blu/blk) is gone. Thanks again for the suggestions--Steve
    '65 911
    '02 M5
    '03 MCS

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