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Carbie Questions

  1. #1
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    Default Carbie Questions

    I bought a 1997 Commander near the end of last season. It has a Marine power 454 with a Holley carb on it. Boat came from Havasu and I live outside Durango, CO read 6000+ ft elevation. I boat here at Navajo lake, but also go to Phoenix, AZ to see family often. Are there any marine carbs I should look at that can change jetting easily ? Thanks boys I know this is THE place for good info.
    Cheers !
    Ron

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    Holley carburetors are about as simple to change main jets on as any. The link may help give you an idea of where to go www.bgsoflex.com/holley.html. You will still have to do some trial and error as every engine set up is different.

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    Simplest thing to do would be to install Holley's quick jet change bowls and a jet "wrench". That way you do not have to remove the bowls for a jet change.
    Another solution would be to install the ProForm "dial-a-jet kit". All jetting adjustments are external on the top of the replaced metering blocks. I think they still sell these kits. Google it. Jocko

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    Default Air Density gauge

    Invest in an "Air Density" gauge and learn how to use it. Buy an assortment of jets, and a notebook. Once you establish a "baseline" of performance at either end of your travels, high or low, you'll be able to make the necessary changes based on "Data", and not some wild guess.... Write it ALL down for future use, you'll be the talk of the lakes when you "hit the tune up" right off the trailer...
    Ray
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    Quote Originally Posted by Moneypit View Post
    Invest in an "Air Density" gauge and learn how to use it. Buy an assortment of jets, and a notebook. Once you establish a "baseline" of performance at either end of your travels, high or low, you'll be able to make the necessary changes based on "Data", and not some wild guess.... Write it ALL down for future use, you'll be the talk of the lakes when you "hit the tune up" right off the trailer...
    Ray
    thats good info right there! You can change jets in a heart beat once you know what works at 6k and what works when the air gets thicker(so to speak) at 1k. Plugs tell the story and a weather station can get confusing. M

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    Quote Originally Posted by fastmarlene View Post
    Holley carburetors are about as simple to change main jets on as any.
    NO! the Holley is probably the worst PITA carb to change jets in. I can't think of another carb that is as bad. Tunable yes, PITA, definitely.
    Quote Originally Posted by jockorace View Post
    Simplest thing to do would be to install Holley's quick jet change bowls and a jet "wrench". That way you do not have to remove the bowls for a jet change.
    Another solution would be to install the ProForm "dial-a-jet kit". All jetting adjustments are external on the top of the replaced metering blocks. I think they still sell these kits. Google it. Jocko
    I agree, that would be the easiest. I don't think Proform ever made the externally adjustable blocks. I believe Percy's is the only one making them. Holley did sell them, but I believe they sold the deal to Percy's or Percy's was always making them for Holley and Holley is no longer distributing them. Anyway, they are available.
    LINK: Percy's externally adjustable metering plates

    The very easiest is Willy's setup, and it doesn't make the carb any longer, and you get a billet metering block in the deal to boot.


    By far the easiest CARB to change jets in is what was the old holley 4010 series carbs now sold exclusively by Summit. You can change the jets in these things in less than half the time of a 4150/4160 Holley. And they are available in manual secondary double pumpers in 600 and 750 sizes.




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    Bob, your right.......I forgot it was Percy's (not Proform) that made that kit. I put one on a generic 1850 Holley on my roadster and it worked really good. It did extend the carb length as you said, requiring longer bowl transfer tubes included in the kit. Jocko

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    Thanks guys ! I knew I came to the right place. All great suggestions, I like the idea of the air density gauge and getting my set up dialed just right. I'm off to do my homework !
    Cheers
    Ron

  11. #9
    Or Seth, either one Budweiser's Avatar
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    Default Dare I even say it? It's true, why not?

    Quote Originally Posted by COKid View Post
    ...Are there any marine carbs I should look at that can change jetting easily ?
    The metering rods (jetting) in a Carter AFB style (Edelbrock) carburetor are THE quickest, cleanest, and easiest to change... At least in my personal experience. It can be done in less than a minute, probably closer to 30 seconds if you don't count the time it takes to remove the air cleaner.

    They are less understood, so less average engine guy tuning advice is available, but it is available. If a simple jetting change is what your after, this may be your ticket. I'm pretty sure Edelbrock has a marine version.

    -Seth-

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    gn7
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    Quote Originally Posted by Budweiser View Post
    The metering rods (jetting) in a Carter AFB style (Edelbrock) carburetor are THE quickest, cleanest, and easiest to change... At least in my personal experience. It can be done in less than a minute, probably closer to 30 seconds if you don't count the time it takes to remove the air cleaner.

    They are less understood, so less average engine guy tuning advice is available, but it is available. If a simple jetting change is what your after, this may be your ticket. I'm pretty sure Edelbrock has a marine version.

    -Seth-
    The rods in a Carter/Edelrock are not a true jet change but more of a fuel curve trim. No different than the needle in a M/C carb slide. You don't re jet a bike with the needle, you trim the fuel curve with it. They will make an overall A/F change, but its minor compared to a jet change. Not usually enough for an altitude change, or a serious air density change.
    Also, they are vac operated and double as the fuel enrichment like a Holley PV
    If you are looking for an across the board fuel delivery change, you have to go inside and change the jets just like a Holley 4010.



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    Last edited by gn7; 04-18-2012 at 09:06 PM.

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    Gn7 Have you looked at a EDE tunning manual lately, up to 22%. Prob. with the EDE is they never keep the power tip constant,like the best carb for this app the Q-Jet. Not too easy to change primaries like the others but who cruises anyway. Q-Jet sec. rod adj. 40 seconds.

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    gn7
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    Quote Originally Posted by MACHINEHEAD1 View Post
    Gn7 Have you looked at a EDE tunning manual lately, up to 22%. Prob. with the EDE is they never keep the power tip constant,like the best carb for this app the Q-Jet. Not too easy to change primaries like the others but who cruises anyway. Q-Jet sec. rod adj. 40 seconds.
    Like I said, it will change the jetting, but its design is to change the CURVE,
    AND
    it is VAC dependent. So its not only like changing a jet, its also like changing the VAC number and the PVR as well, all at the same time. Not EXACTLY the EASIEST change in the carb tuning for alttitude/air density change.

    When I make a change in a Holley, I usually don't change ALL those things at the same time, specially because I climbed a few thousand feet, or the weather changed.



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    You have a holley, get the Percys frt. and rr. ($270) And an O2 and AD gauge ($370 5-wire and $120), and the binder and pen ($8) and a dyno with a good opperator to enterpolate the numbers ($625). Or just read the plugs! I dont think its going to hurt its self if its too rich. Oh, get the dry tips so the O2 wont crumble. ($600-$6800) Oh boy! I think you just bought (dare I say it) E F I

  16. #14
    Or Seth, either one Budweiser's Avatar
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    Quote Originally Posted by gn7 View Post
    The rods in a Carter/Edelrock are not a true jet change but more of a fuel curve trim. No different than the needle in a M/C carb slide. You don't re jet a bike with the needle, you trim the fuel curve with it. They will make an overall A/F change, but its minor compared to a jet change. Not usually enough for an altitude change, or a serious air density change.
    Also, they are vac operated and double as the fuel enrichment like a Holley PV
    If you are looking for an across the board fuel delivery change, you have to go inside and change the jets just like a Holley 4010.
    I know that you know what you're talking about, just clearing a few things up for accuracy.

    There are, in fact, 4 screw in jets in an AFB style carburetor.
    The secondary jets meter fuel in the traditional sense, solely based on the diameter (area) of the hole in the jet. (along with air bleeds, but we'll leave that alone for now)
    The primary side of the carburetor uses a large jet and a metering rod. The metering rod has two distinct diameters (thin at the tip and thicker above) and slides up and down inside the jet, increasing and reducing the overall area of the jet and fuel flow based on engine vacuum.
    The larger portion of the metering rod (and its relation in size to the jet) could be compared to a main jet in a Holley. Changing the diameter of this portion of the rod IS IN FACT directly related to a jet change when speaking in Holley terminology. However, it's the combination of the jet and metering rod that is important, not one or the other.

    Navaho Lake is at 6086' elevation and Phoenix is 1124', a difference of 4962 (5000). A quick look at Edelbrocks Reference chart reveals this MAY be able to be tuned with a simple metering rod change. Although, I agree with you, it probably will need a different jet(s) and metering rod to get it spot on. (Intentionally left out other air density factors for simplicity)


    Quote Originally Posted by gn7 View Post
    Like I said, it will change the jetting, but its design is to change the CURVE,
    AND
    it is VAC dependent. So its not only like changing a jet, its also like changing the VAC number and the PVR as well, all at the same time. Not EXACTLY the EASIEST change in the carb tuning for alttitude/air density change.

    When I make a change in a Holley, I usually don't change ALL those things at the same time, specially because I climbed a few thousand feet, or the weather changed.
    I completely disagree on this statement.

    The thin part of the metering rod (and it's relation in size to the jet) determines the amount of fuel that flows through the jet under high load (low vacuum) situations. The metering rod in and of itself, has absolutely nothing to do with vacuum at all, ONLY fuel volume (flow). Basically a Power Valve Circuit Restrictor (PVCR) in Holley terms.

    However, changing the spring under the metering rod is just like changing a Power Valve VAC number on a Holley and will determine the point of vacuum it takes to enrich the AFR.

    Either can be changed independently and have their own function.

    I think your use or the term "CURVE" is very loose. Any change to any carb will change the "curve".

    If my goal was easy jet changes, the AFB would be my choice. Even if I did have to pop the lid off. Very easy and quick... and no mess. Although any of the other carbs mentioned will work well too.
    Last edited by Budweiser; 04-19-2012 at 05:01 PM.

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