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Thread: 3000 rpms and runs on 5

  1. #1
    Formerly known as Koalia Reverend's Avatar
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    Default 3000 rpms and runs on 5

    I have this weird issue. Installed set of SK carbs this spring and had the tuned by pro. Been driving since with no problems until now, i cannot accelerate properly because one of the cylinders drop out around 3000 rpms. I have renewed all the plugs plus wires are only year old. Im also running no-points ignition so that is not the problem.

    To me it feels like it could be carb related, but also could be fuel related issue. I dont really know. I have holley regulator and i have cut down that pressure a bit, but do not know the pressure in system, because i dont have gauge for that.

    All help appreciated.
    -72 240Z "Goldie"

  2. #2
    Nova Scotia,Canada,Earth Blue's Avatar
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    Please do these two tests:

    1. What do the plugs look like after you idle it for 5 minutes

    2. What do the plugs look like after you drive at cruise for 5 minutes (do a plug cut and take them out on the side of the road... a photo of all 6 side by side would be nice for us to see)
    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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    ZCars in Eastern Canada seaport ready for shipment to Europe

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  3. #3
    Formerly known as Koalia Reverend's Avatar
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    Well the old plugs were all black as a night. All.
    -72 240Z "Goldie"

  4. #4
    Nova Scotia,Canada,Earth Blue's Avatar
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    That is the problem and it is common to all 3 of your carbs. Try cleaning the plugs and see if they foul with carbon again.


    Wrong jets could be the cause but if it ran well all summer then it must be something else.... too much fuel pressure could cause main overflow into the aux venturi that you should see as fuel dripping out of the throat at idle (remove filters to watch/feel for fuel leaking into the throat). Of course measuring fuel pressure is best.

    Check fuel levels too (in main well).

    Btw did your carbs come in contact and catch the illness that Madkaw has?
    Last edited by Blue; 08-19-2014 at 01:11 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


  5. #5
    Registered User rossiz's Avatar
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    Madkaw disease!
    Blue likes this.
    '78 280z - Daily driver/work in progress...

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