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Thread: holley jet size

  1. #1
    Senior Member EXPERT BUILDER
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    holley jet size

    how do u determine what size the jets are
    and also how do u know what size to change to
    cus im runnin real real rich and i need to jet it down some

  2. #2
    Senior Member RACING JUNKIE
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    there is a number stamped on the side of the jet...example 68.

    I change jets 2 sizes at a time until it's where I want it. You can go by the plug reading, mph(race car) or use an EGT to decide which way to go. Street car I'd just jet it to where it runs the best without loading up at slow speeds. Make sure the power valve is correct for the amount of vaccume you have at idle in gear.

  3. #3
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    ooo ok

  4. #4
    Senior Member RACING JUNKIE BEAST477's Avatar
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    bohay, to determine jet size you have to remove the float bowl. The jets are located in the metering block. They will have a number stamped on them. Also are you rich at idle,mid range, or top end? Check your idle mixture screws on the sides of the metering block. Turn them all the way in then back them out 1 1/4 to 1 1/2 turns to start. Also while you have the bowls off check the power valve make sure it's not blown or does it have a plug? I know it's alot but you need to check it all.
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  5. #5
    Senior Member RACING JUNKIE BEAST477's Avatar
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    Damn tod I type too slow.
    BEAST477






    Only a rich man can afford to use cheap parts.

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  6. #6
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    how would u tell if the power valve is blown or has a plug,
    i found it and have it out and i dont know how to tell wether its the right one for the vacume i have

  7. #7
    Senior Member RACING JUNKIE
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    IF IT IS A PLUG IT WILL BE OBVIOUS. A powervalve will have a spring and a diaphram,and a number on it like 65 which means 6.5 inches of vac ume is the opening point.when it opens it will enrichen the mix 8-10 jet sizes. Put a vacume gauge on the car and put it in gear and let it idle. Use a PV rated just below the reading on the gauge,so it doesn't open at idle but will open as soon as the vacume drops when you wood it..Almost all will have a 65 in them stock. They make a PV tester but you can usually tell if they are blown by sucking on them...if it opens and closes when you gently suck on it from the side opposite the spring it should be good. You could also probably put some fuel in the float bowl and hold the metering block on with your hands and hold it up and see if any fuel runs out....it shouldn't run out of the pv.

  8. #8
    Senior Member MASTER BUILDER
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    YEP!

    X2 what Todd said. Did you get all of that Bowhay?

  9. #9
    Senior Member RACING JUNKIE
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    Another thing BOWHAY...if it is running fat at idle and you get no response to turning the idle mixture screws in the metering block, that normally means you have the idle speed screw opened up too far and are exposing too much of the transfer slot in the base plate...when that happens you start to draw from the main circuit instead of the idle circuit.


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