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Thread: Power difference between dual vs, tripple carbs on 240Z

  1. #1
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    Oct 2013
    Cache Valley Utah

    Default Power difference between dual vs, tripple carbs on 240Z

    I have the opportunity to get a 73 Datsun 240z (my brothers) that hasn't been ran in many years (like 15 or so!) The engine has been stroked (280 Crank in 240 block), cam, head work etc. It currently has triple Webers on it an he has two sets of the early SU's (I believe they are from a 70-71 240z). He also has a 5 speed trans w/ matching rear end to put in.

    I know a lot desire the 3 Webers and it was a blast to drive but very temperamental. I want to use it as a daily driver (even in the winter here in UT). I don't mind tuning every so often.

    I have driven a 240z with the stock SU and it was still fun.

    So my questions would be-

    1- On my engine, how much difference is there going to be with the dual vs triple setup.
    2- How much engine mod can the dual SU's handle?
    3- Is there some mods that could be done to the SU's that would make them perform a lil better without messing them up?

    Thanks for any help. If some of this has already been answered can someone post a link to the topic please.

    I did search around a bit and couldn't find what I was looking for.

  2. #2
    Nova Scotia,Canada,Earth Blue's Avatar
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    Jan 2005


    1. SU's would be better for a daily driver. You will loose some low end torque.
    2. SU's can handle everything, even turbos! No worries there
    3. SU's first need to be tuned. Mods can follow depending on what you need:
    - piston at top limit at a particular rpm (spring and weight)
    - increasing piston top limit (shaving plunger tube metal and removing washer/stopper)
    - needle change to get fuel ratio set for power or mileage or compromise
    - piston rate change (oil)
    - air flow over bridge and under piston (metal shaping)
    - increasing air flow (boring)
    - reducing throttle valve obstruction (tapering profile)
    - increasing air flow (low profile elliptical bellmouth)
    - reducing heat transfer (exhaust heat shields and doubling up on insulators)
    Last edited by Blue; 05-23-2014 at 08:23 PM.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.

    John Ruskin (1819 - 1900)

    ZCars in Eastern Canada seaport ready for shipment to Europe

  3. #3
    Registered User george71z's Avatar
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    Feb 2002
    Melbourne, Florida


    I had triple Webers on my '71 for years. Big bog at low end, until I put in a new engine w/ a performance cam. The linkage is critical. Make sure your linkage is rock solid and opening all carbs at the same time. I also used a Color-tune glass sparkplug to set mixture. Ran great with almost no need for constant adjustment. Only drawback was it used 1/3 more gas than the SU's.
    72 240-- stock motor and drivetrain, 50,500 orig. miles

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