Carb jets and altitude
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Carb jets and altitude

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    Senior Member activeshack's Avatar
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    Default Carb jets and altitude

    1976 Spectra Daycruiser running a ZZ502 Chevy crate motor with a tunnel ram and 660 center squirter Holleys. Have the carbs jetted with 72s which was ideal at sea level in Virginia. I'm living in Colorado now and thinking about bringing the boat out here. Will I need to change jets in the carbs ? Will the altitude at 8000' change the lean/rich mix ? Running 100LL because of the glass tanks.

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    Member sneakyneon's Avatar
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    you will be down 100 to 120 HP from sea level I would jet down 4 and would expect more. No way to know exactly, its trail and error

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    Senior Member activeshack's Avatar
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    Quote Originally Posted by sneakyneon View Post
    you will be down 100 to 120 HP from sea level I would jet down 4 and would expect more. No way to know exactly, its trail and error
    .
    New I would lose some HP so probably start with 68s and check the plugs ?

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    Senior Member SoldHondaBoughtHondo's Avatar
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    How much change in temp/humidity?
    Air Density Calculator
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    Senior Member activeshack's Avatar
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    Quote Originally Posted by SoldHondaBoughtHondo View Post
    How much change in temp/humidity?
    Air Density Calculator
    Now this is getting way too complicated lol

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    Quote Originally Posted by activeshack View Post
    Now this is getting way too complicated lol
    Easy enough, throw some 68's in it and take it out. It will be so far down on hp you might not want to even use it....
    And bring some 02 for you to
    You need to buy one of those units with an altitude compensator pulley on it, that will get the hp back, still have to mess with jetting but it's much more fun.
    "A liberal paradise would be a place where everybody has
    guaranteed employment, free comprehensive healthcare, free
    education, free food, free housing, free clothing, free
    utilities, and only law enforcement has guns. And believe it or
    not, such a place does, indeed, exist: It's called prison."

    Sheriff Joe Arpaio
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    My typical lake conditions result in a result of .0607. What is that number. How do I use it to figure out density altitude?

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    not sure if this helps, but I am looking for initial jets and saw this:

    Interactive Holley Jet Correction Program

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    Senior Member bp298's Avatar
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    Quote Originally Posted by SoldHondaBoughtHondo View Post
    How much change in temp/humidity?
    Air Density Calculator
    what exactly is this supposed to be useful for???

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    Quote Originally Posted by bp298 View Post
    what exactly is this supposed to be useful for???
    Maybe for increasing his post count?

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    Senior Member SBS933's Avatar
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    Dump some propylene oxide in the fuel and mash the pedal. DUH
    Last edited by SBS933; 03-31-2014 at 09:30 PM.
    Believe Nothing you hear and 1/2 of what you see.

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    Senior Member activeshack's Avatar
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    It looks like either 76s or 78s are what I'll need so I'm going to try the 78s first. Would rather be a little on the rich side versus lean to start with.

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    I would go leaner your going way richer if you buy those jets you need to try like 69 if you have 72s. I boat at 6200' and i go up 3 to 4 sizes going to Laughlin.

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    Senior Member activeshack's Avatar
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    Quote Originally Posted by 88hardin View Post
    I would go leaner your going way richer if you buy those jets you need to try like 69 if you have 72s. I boat at 6200' and i go up 3 to 4 sizes going to Laughlin.
    What's the altitude at Laughlin ? I've always boated at sea level on the Chesapeake Bay and it's tributaries so this altitude is all new to me. I've got a complete Holley jet kit with everything from like 60 to 80.

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