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Thread: Carb trouble

  1. #1
    Registered User maton_acoustic's Avatar
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    Default Carb trouble

    Hi, I've reached the carb set up stage of my restoration now. I've got a colour tune and a uni-syn so I started with trying to balance air flow.
    I set the uni-syn so the front carb bought the little float up to around the centre mark of the tube and then tried the rear carb and it's not even registering on the uni-syn at all.
    I would screw in the throttle screw but at the moment the rpm is really high even though I've got both individual throttle screws backed out all the way, and the screw on the main throttle linkage is also backed off all the way.

    I read somewhere to check for vacuum leaks with carb cleaner so I will try that tomorrow but I was wondering if someone could give me some advice and things to check.
    I've never worked on carbs before so my knowledge is very limited but I'm keen to learn.

    Many thanks.

  2. #2
    Barn Find Daily Driver Captain_Zeros's Avatar
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    Default

    Make sure your float bowl levels are dead on. The mix screw is really only a fine adjust.
    1973 240Z w/ roundtop carbs, 280zx e12-80 distributor, 280zx alternator, late model Altima junkyard electric fans. 115 Blue Metallic & white side stripes.

  3. #3
    Registered User beermanpete's Avatar
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    Default

    Make sure the throttle linkage is adjusted properly. If one of the rods is a bit short it will hold the throttle open. The carbs should both be able to close fully with the throttle stop screws backed out all the way.

  4. #4
    Registered User madkaw's Avatar
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    Default

    One way to be sure is remove that carb and see if the butterfly is open at all. It wouldn't take much air to slip by. You could use a feeler gauge or probably could see visually if its open at all. If it is , ten your linkage is probably at fault.
    It's only four nuts!!
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  5. #5
    Registered User maton_acoustic's Avatar
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    Ok cheers guys. I'll give that a go

  6. #6
    Registered User Stanley's Avatar
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    Default

    You checked the idle adjusting screws, first step, right? They're on each carb body right where the linkage between the carbs meets the carbs. Move them both all the way up or all the way down, and then screw each the same number of turns until they're in the middle where the idle is about right. Then set the balance, mix, fast balance, readjust the idle screws, and repeat.
    In case I left something out, the FSM tells it best.

  7. #7
    Registered User z74z90's Avatar
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    I find that this is very helpful....good luck!

    TECHNICAL TIP #6

    1974 260Z 2+2
    Member, Indy Z Car Club
    Member, Windy City Z

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