Holley Jetting
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Holley Jetting

  1. #1
    AAARRRRRGGGGGGG!!!!! Motomatt68's Avatar
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    Default Holley Jetting

    This is my first time working with a Holley carb. I have a 750 vacuum secondary 4160 on a 509 bbc in a whitewater jet boat. I am making about 400-450 hp at 4400 rpm depending on what impeller chart you look at. I ran the motor at about 3300 rpm (just above cruising rpm) for 45 seconds and shut it off as soon as it went down to idle. How much of a jet change should I make.



    Matt.

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    Default New plug??

    That can't be a new spark plug... Unloaded RPMs won't really tell you anything... From what I see there, it's fat, and has been for a while... More than that, it looks like it's getting fuel from somewhere besides the main jets...Like maybe a blown P/Valve dumping raw fuel into the intake...
    Ray
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    Senior Member earlbrown's Avatar
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    when you were cruising at 3300 what was your vacuum reading and what powervalve do you have?

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    Quote Originally Posted by Moneypit View Post
    That can't be a new spark plug... Unloaded RPMs won't really tell you anything... From what I see there, it's fat, and has been for a while... More than that, it looks like it's getting fuel from somewhere besides the main jets...Like maybe a blown P/Valve dumping raw fuel into the intake...
    Ray
    Ray knows what he's talking about here-what he didn't mention is you need to use a NEW set of plugs and run them and cut it off after your run- not idle to shore-then read the color to adjust your mix.make sure you check the p-valve.
    If that was a new plug you are WAY fat.
    Last edited by Ronboats; 08-28-2012 at 10:23 PM.

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    That is not a new plug. I didn't know I needed new. I will get some and redo the test.

    I don't have a vacuum gauge set up. It is a jet so running it on the trailer with the back end in the water should be under load. I didn't idle after I just ran it and shut it off as soon as it got close to idle. I was told that I didn't have to do wot runs just under load above where I cruise.

    Do I need a new set of plugs or can I just change one and see how it does?

    Do I need wot? and does the engine have to be completely up to temperature?

    If it does need to be warm then I need to run for a while, change plugs, run it hard once, and check the plugs immediately. And I should do this every time I change jetting? Is this right?

    Is there a way to clean a plug. It seems like if I have to buy a new set for each time I check it could get expensive fast. Not that any of this is cheap.

    Matt.

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    gn7
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    Yes you do need to run it WOT max RPM. Everything else below that is the "fuel curve" and is probably outside your ability to change aside from a PV change.
    Yes, you need to be up to temperature, one because it has some effect on jetting, but more important, you don't want to run your boat WOT when its not!!!!
    Yes you need new plugs. MIGHT be able to read those, if you can hold WOT for 3 minutes or more so you can burn them clean. That is once you get your mixture somewhere near correct.
    If you're only interested in the mixture in one cyclinder, you can use one new plug.
    No you cannot do this on the trailer back into the water under full load.
    No you cannot clean the plug.

    Matt, you could POSSIBLY save yourself a ton of grief by telling us what size the carb is, what the current jetting is, what the current PV vacuum number is, are there pri and sec PVs, what the size of the engine is, compression ratio, cam type and roughly the profile. Wet logs, dry headers, wet headers?

    Showing us a plug that bad, and asking what the jetting should be is IMPOSSIBLE!



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    AAARRRRRGGGGGGG!!!!! Motomatt68's Avatar
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    Holley 750cfm vacuum secondary. 509 bbc at about 8.75:1. AFR 305 CNC'd with hydrolic roller about .622 intake and .617 exhaust 112* lsa. Dana wet headers. I don't have the jetting or pv info here but I will get it.

    I don't know anything about holleys so I will be reading and may be able to answer more soon...

    Engine makes about 400-450 hp at 4400 right now. I plan on cutting the impeller to let it get up in the hp more but that is later. I am having proposing problems so running it under full power for 30 seconds to a minute is scary. Hopefully I will get it running at the right attitude this weekend so I can get this done safely.

    Thanks for the replies so far, Matt.

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    Ps. Since I didnt know i needed a new plug I use what was in it. They were sooty from when I was first trying my EFI and it ran unbelievably rich. The water out the exhaust was black. I assumed running it hard for a while would cook off anything on there...live and learn.

    Matt

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    Default So...maybe....

    Quote Originally Posted by Motomatt68 View Post
    Ps. Since I didnt know i needed a new plug I use what was in it. They were sooty from when I was first trying my EFI and it ran unbelievably rich. The water out the exhaust was black. I assumed running it hard for a while would cook off anything on there...live and learn.

    Matt
    Soooo, we dig a little deeper... Maybe it's not fat now, and maybe, it doesn't have a blown Power valve.... Trying to use those plugs for any sort of current information is, as Bob said, impossible.. Can you clean them? Well, yeah... If you had a a/f ratio leaning toward lean, and could run it WOT, at a good solid operating temperature, for an extended period of time, they MIGHT clean up.....But, since you can't do that, it looks like you're going to have to pony up the coin for some new ones... BUT, You might want to mention the plug number, as you could be waaaay cold on the plug heat range and all the tests in the world won't yield any decent info as to a/f ratio...( Lucky for me, I use an EGT in a dry header to establish A/f ratio and don't ever have to look at a plug....)..... Get the boat right to SAFELY do some WOT runs, and pull a plug before you let it idle for more than a few seconds..... Then, show us some pictures of your results and someone here will nail it down for you....I will ad, that if you need to change more than 4 jet sizes, up, or down, the carb is likely the wrong CFM for your application.... IMO, you'll have a double pumper, with some "shooter" work, on it before you're happy with the results....
    Ray
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    I already ordered some plugs and they will be here by this weekend. The plug is an ar3932. It is the plug AFR recommended for my head. I will be working on the porpoising this weekend and it should be a relatively easy fix. I will post when I get more info.

    Thanks, Matt.

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    Super Moderator HammerDown's Avatar
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    Matt when first experimentation with my Jet (16 years ago) my plugs were somewhat but NOT as dark as yours.
    As mentioned, make sure to use a vacuum gauge to help determine the proper power valve needed > this was a BIG aid!
    Make sure the carb is CLEAN, float level is right > and no air bleeds are clogged!
    And of course, make sure you have the correct heat range plug or error on the cooler side if guessing.

    With the above and help from the gurus here, I ended up with this > it's a 'more-happy' plug
    You can't see it but, way down in the plug I can see the 'fuel ring' > this was after a 1/4 mile WOT pass then, a 'safe' but quick shut-down.
    BTW, if and (hopefully) all your plugs look and are burning the same...if so, you don't need to do your 'testing' with new plugs each time > I only checked and made jet adjustments using two new plugs.

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    gn7
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    Quote Originally Posted by Motomatt68 View Post
    I already ordered some plugs and they will be here by this weekend. The plug is an ar3932. It is the plug AFR recommended for my head. I will be working on the porpoising this weekend and it should be a relatively easy fix. I will post when I get more info.

    Thanks, Matt.
    Matt, the heads do not determine the plug heat range, other than being alum or iron. When AFR recommends a 3932 plug, they aren't talking about a 8.75 CR engine with a cam that lumpy. What is the .050 of that cam? How do you come up with that cam for that combo?

    That plug is EXTREMELY COLD. In a 8.75 CR engine, with alumn heads and that camshaft, it has no chance. Make the carb even a little rich, and it is hopeless. I have never run a plug that cold in a blown engine spinning twice the RPM.

    Also, its a racing plug which why you have to order them. You can get a good decent plug for that deal off the shelf unless you live in Siberia. You don't live in Siberia do you?
    I would use a NGK 2756
    If you get Autolites easier than NGK, I would try a 5224 or a 3924.

    don't even atempt to tune that thing with a plug that cold.


    I



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    I found the specs on the cam. Adv dur 292/300. Dur @0.050 242/248. Lsa112 lift .622/.617.

    I will get some of the NGK's you recommended and make some passes this weekend. I have some solutions to the porpoising problem so I can make some fast passes.

    Matt.

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    I took the boat out yesterday and the engine ran great but since I was at 7500' I didnt do any testing with the plugs. I hope to get out on the river here and check. I have a set of the autolite 3924's which gn7 recommended and I will use them.

    Does anyone use the adjust-a-jets that you can get for holley carbs. They seem like a good way to go since I boat from 3500' to 7500' from weekend to weekend but I really dont know anything about them. Most of the criticism that I have read is that it lengthens the carb (which is not a problem for me) and once you get things set you dont mess with them so why have something adjustable.

    Is it worth getting a wide band o2 meter and adjustable jet plates. The money is not an issue but spilling gas in the engine bay to change jets (my engine is enclosed) seems like it could be dangerous.

    What is a good wide band o2 meter and are the adjust-a-jet plates decent or a gimic?

    Thanks, Matt.

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