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Thread: Running very rich and mixture screw question

  1. #1
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    Default Running very rich and mixture screw question

    I have a 260z with 3 screw carbs. It is running so rich that the fresh oil on a fresh rebuild is dirty and fuel smelling with only 2.5 hours of driveway idle time on it. Carbon fouled plugs, toxic exhaust. You get the picture. I spoke to Bruce the other day and was given some great hints. In any case I took the pistons out today to check the needle jet height and found that no matter which way you turn the mixture screw located under the carbs -all the way in either direction it seems my jet does not move. I have included some photos. I guess I am trying to understand what part of the jet is susposed to move. I assume it is the center bit, the part that is down about 3/16 below the bridge. Is this correct. Would I actually see visual movement of the jet if I crank the adjustment screw all the way in either direction.

    Thanks
    Glenn
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  2. #2
    Registered User Zforce's Avatar
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    Default

    Also check your floats, they may be sunk.

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    Clean and lube the carb:

    0. Make sure the choke connection to the jet works correctly and the jets raise and lower easily with the choke cables.

    1. Take out the jet and clean it as well as the tube where it fits. Spray carb cleaner works great

    2. Once cleaned insert the jet and move it by hand up and down. Check for binding.

    3. If it still binds, you may wish to gently sand jet with emery paper to help.

    PS Spray carb cleaner on all that black stuff and wipe with blue shop rags until just grey aluminum. Do the same for the pistons and domes. Clean carbs work better than carbon-gummed carbs.
    Last edited by Blue; 06-19-2011 at 12:14 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.


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    By the way currently the choke cables are not hooked up. Would this matter at all, the jet should still move when the adjustment screw is turned. Correct?

    Thanks
    Glenn

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    What does sunk mean, broken and filled with gas so they wont lift? please clarify

    Thnaks
    Glenn

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    Nova Scotia,Canada,Earth Blue's Avatar
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    Not having the chokes hooked up makes it easier.

    When you turn the knurled screw to bring jet all the way up until it stops, the top of the jet should be flush with the brass cylinder top that the jet resides in. The jet should move easily when the knurled screw is turned by hand. Any binding will be caused by gunk or corrosion between the jet and the sleeve (brass cylinder in which the jet moves).


    After you get the jets moving freely in their sleeves, the needle should be set to it drops all the way down and it's shoulder sits on top of the jet and effectively closes the space between the two.
    Last edited by Blue; 06-19-2011 at 01:44 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

    http://ZSportCanada.com


  7. #7
    Registered User Zforce's Avatar
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    Quote Originally Posted by zdude1967 View Post
    What does sunk mean, broken and filled with gas so they wont lift? please clarify

    Thnaks
    Glenn
    Yes they can become soaked with fuel making them heavy.

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    Thanks Gentlemen. I am off to the garage with some cold beverages and this information.

    Cheers
    Glenn

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