holley main jet fine tuning
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holley main jet fine tuning

  1. #1
    Steady Rollin
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    Default holley main jet fine tuning

    the carb is a Holley 4150

    So new to me boat, I've had it out a couple times at the local lakes. The previous owner mentioned he recently went up in size and was thinking it might have been too much.

    Any seat of the pants tests I can run to figure out if its should be rolled back to the old jets? Plug chops are kind of a pain to do on a running river, but I could try it
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    Village Idiot fc-Pilot's Avatar
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    Hand held GPS works, or worse case would be a recall tach to see what your max RPM's is. Just some quick ideas. O2 would be great, but can lead you astray if you are dead set on looking for a number instead of using it as a guide.

    Paul

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    Senior Member Bubbletop409's Avatar
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    You can get the list number from the carb and go to Holleys web site and find out what the original factory jetting, power valves, squirters, etc. were.
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    Quote Originally Posted by fc-Pilot View Post
    Hand held GPS works, or worse case would be a recall tach to see what your max RPM's is. Just some quick ideas. O2 would be great, but can lead you astray if you are dead set on looking for a number instead of using it as a guide.

    Paul

    So logic being at the top end it'll net the most RPM which translates into MPH.

    makes sense.
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    Senior Member jockorace's Avatar
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    If you know how to read plugs.......do it! If you don't know how, bring someone with you that can.
    The easy way is to bring a few spare plugs, chop the power and pull the plug on #7 (if flywheel forward) and quickly put the spare plug in. You should be able to do that in about 30 seconds, so it's still feasible on the river. JMO, Jocko

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    This^^^^^^even if you cannot chop it clean,Bring it in as quick as possible and read the plugs that should tell you something.

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    Quote Originally Posted by Bubbletop409 View Post
    You can get the list number from the carb and go to Holleys web site and find out what the original factory jetting, power valves, squirters, etc. were.
    If the air horns are cut off then get a butterfly size. You can identify the CFM from that.M

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    Default How serious are you?

    OK, as mentioned you should have an accurate GPS and a memory type tach. AND a new notebook.... Changing ONE thing at a time in the direction of improvement, or loss..... Then, call Kinsler and buy an "Air Density Gauge" so you can compare apples to apples instead of chasing your tail through varying atmosphere conditions... Once a base line is established at a given "Air" reading you can easily calculate what jet to change to and get the same, (very close) result.. (Less air means less performance, plain and simple, the air dictates the fuel. Less fuel= less performance).... Obtain a jet chart that shows the AREA of various jets and use that to add, or take away fuel, based on percentage differences in density and percentages of AREA, (NOT DIAMETER).... Sure, you can say a 76 jet will flow more than a 74, but how much more??
    After any, and all changes, WRITE IT DOWN, as well as the performance gained or lost...

    Ray
    PS The chart will show area out to 5 or 6 places past the decimal point... You can also do the math, but the chart is much quicker...
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    Senior Member jockorace's Avatar
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    Quote Originally Posted by ol guy View Post
    If the air horns are cut off then get a butterfly size. You can identify the CFM from that.M
    Mark is right......in most cases. However, check out this chart.
    With 5 different CFM carbs listed here, there are only 2 different butterfly sizes. Plus, Holley had to put their HP950 into the list somewhere. I find it odd that an 850 has the same butterfly size and a largerventuri size as the HP950.......and it flows 100cfm less!? Jocko
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    Last edited by jockorace; 02-12-2018 at 09:46 AM.

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    The mechanical Kinsler Gauge is better than nothing but an electronic gauge that figures temperature, humidity and barometric pressure into the calculation is better. A general rule of thumb is a 3% change in air density is one jet size.
    GD

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    Quote Originally Posted by Moneypit View Post
    OK, as mentioned you should have an accurate GPS and a memory type tach. AND a new notebook.... Changing ONE thing at a time in the direction of improvement, or loss..... Then, call Kinsler and buy an "Air Density Gauge" so you can compare apples to apples instead of chasing your tail through varying atmosphere conditions... Once a base line is established at a given "Air" reading you can easily calculate what jet to change to and get the same, (very close) result.. (Less air means less performance, plain and simple, the air dictates the fuel. Less fuel= less performance).... Obtain a jet chart that shows the AREA of various jets and use that to add, or take away fuel, based on percentage differences in density and percentages of AREA, (NOT DIAMETER).... Sure, you can say a 76 jet will flow more than a 74, but how much more??
    After any, and all changes, WRITE IT DOWN, as well as the performance gained or lost...

    Ray
    PS The chart will show area out to 5 or 6 places past the decimal point... You can also do the math, but the chart is much quicker...

    Definitely not that serious, I'm just looking to go for good power, optimal fuel. This is not race setup

    I'll check the plugs and do the best i can with mph/rpm

    thanks guys
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    Senior Member ol guy's Avatar
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    Quote Originally Posted by sintax View Post
    Definitely not that serious, I'm just looking to go for good power, optimal fuel. This is not race setup

    I'll check the plugs and do the best i can with mph/rpm

    thanks guys
    If you want a good baseline tune without all the computer and weather station tuning I would get a starting point from Holley and start there. At that point you can tune by seat of the pants. Engine size, additions, cam and ignition. Mostly carb size for application would be a BIG plus. Not to scare you but the more info you have the more info you are going to get here. M Addition, If you don't know the carb bring it to me and I would be happy to identify and check jet,squirter, and power valves you have as we speak. Mark
    Last edited by ol guy; 02-13-2018 at 06:59 PM.

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