single 4 barrell tuning help
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single 4 barrell tuning help

  1. #1
    Senior Member glastornjet73's Avatar
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    Default single 4 barrell tuning help

    I have a jet boat 455 olds mild engine 11-1 comp, alum heads, around 550 lift cam, all ballanced zero decked extencive time spend to make it live but getting to the nitty gritty 830 hp downleg booster holley conpletly factory specs except for holley calls for 86's square and i have 84's square 6.5 power valves front and rear front 2 plugs are a little on the rich side 3/4 a little fatter 5/6 sooty 7/8 wet where would you start off i was thinking about doing away with the rear power valve completly and trying a 4.5 in the front and starting there i am pretty decent and tuning carbs but i am new to tuning them on a boat i know the metering and needs of a marine engine are diffrent than there land going counterparts so i figured id try and get some input on here before trying much if it were a car doing that i would change the power valves but indont know if it maybe need the fuel because it is under more of a load than it would be if it were in a car maybe im just overthinking this (i tend to do that from time to time)

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    gn7
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    The amount of raw fuel in the manifold, with the engine tilt back + the attitude of the boat are causing to be richer and richer towards the back.

    Shit can the secondary PV all together. You can't open the secondaries without it activating anyway, so why have it. If the secondaries are open even a little, the PV is open.

    A 4.5 in the front may help. I'd keep the secondary jetting and drop 4-6 from the front.

    What manifold are you running, and does it have a spacer? 4 hole or open?



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    Senior Member glastornjet73's Avatar
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    Quote Originally Posted by gn7 View Post
    The amount of raw fuel in the manifold, with the engine tilt back + the attitude of the boat are causing to be richer and richer towards the back.

    Shit can the secondary PV all together. You can't open the secondaries without it activating anyway, so why have it. If the secondaries are open even a little, the PV is open.

    A 4.5 in the front may help. I'd keep the secondary jetting and drop 4-6 from the front.

    What manifold are you running, and does it have a spacer? 4 hole or open?
    I am using a crosswind intake (everyone says they are the catts a$$ for olds jet boats) idk lol but i am running a 2" 4 hole to open hvh super sucker spacer but i am gonna bail that in favor of a 1" 4 hole i just never get time to run to the local performance shop before they close... Thats exactly what i had in mind about the back holley said to ditch the back pv and up the jet size 6-8 numbers over factory size!!! Thats where he lost me 86+6 is 92!!!! Thats way into alky territory for cryin out loud!

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    gn7
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    The Supersucker is not your friend unless you need it it to reach your desired RPM. On a Olds I am not sure you care to run it to the point the thing is a benefit. Just changing the spacer to a 4 hole is going to have an effect.

    You are trying to remove "jet", not make up for a removed PV. If your tune was fine, then the recommended increase would make sense.



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    Senior Member glastornjet73's Avatar
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    Quote Originally Posted by gn7 View Post
    The Supersucker is not your friend unless you need it it to reach your desired RPM. On a Olds I am not sure you care to run it to the point the thing is a benefit. Just changing the spacer to a 4 hole is going to have an effect.

    You are trying to remove "jet", not make up for a removed PV. If your tune was fine, then the recommended increase would make sense.
    Yeah i am goin to get another spacer this week deffinatly the only reason its on there is i cant bolt the carb directly to the intake the fuel lines will hit so i need at least a 1" spacer would you say an open or a 4 hole i was gonna do a 4 hole... And after that i will do the pv blockoff and maybe drop to an 80 in the primarys?

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    gn7
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    I should have said this in the very first post, but I always seem to make the "assumption"!!

    DOUBLE CHECK THE FLOAT LEVELS!!!!



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    Senior Member glastornjet73's Avatar
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    Lol yeah i guess i should have mensioned that if anything they are a touch low 1/16 or so below the sight plug holebut maybe they need to be lower by the time it gets on plain i guess it could be a little high i guess i could take the real plug out hold my finger over the hole and let someone else drive and get it on plane and re check em sounds kinda dangerous tho lol

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    gn7
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    Quote Originally Posted by glastornjet73 View Post
    Lol yeah i guess i should have mensioned that if anything they are a touch low 1/16 or so below the sight plug holebut maybe they need to be lower by the time it gets on plain i guess it could be a little high i guess i could take the real plug out hold my finger over the hole and let someone else drive and get it on plane and re check em sounds kinda dangerous tho lol
    If they are right at the bottom of the site plug when you shut it off, they are fine.



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    Cool ill check em again today just to make sure but i have checked em 2/3 times and ill make sure and run to the performance shop this week and get a pv block off and a 1" spacer... I think im gonna bring a vacuum gauge with me today and see what the vacuum is around 3800/4200 because most of the time i cruise around there do you think i should bring the pv in a little before my cruising rpm or just after?

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    Question/comment...if the enrichment device (power valve) is designed to "add fuel" at a specific vacuum signal and below then why not keep it?

    Reason.. why remove/block the secondary PV and jet-up 6-8+ sizes to where (and just getting into the secondaries) you're dumping more fuel than what really may be needed vs, using smaller 'secondary-jets' and allowing the PV to open as intended and 'just before' WOT ?

    Of course...the above all comes into play with 'vacuum signal'...and the reason to test different vacuum readings at different RPM levels from idle, all the way up to WOT.

    Yesterday...(and FINALLY) gearing-up to change-out my '850 Annular DP' to a (hopefully) more fuel friendly '850 Vacuum Secondary carb' I boated around with a vacuum gauge in hand (hooked-up to an intake manifold port) and ran at different RPM's noteing vacuum readings to know what PV would be best suited at
    wot AND 'upper RPM' range.

    Results...at WOT-PUNCH and a ZERO vacuum reading tells me a 6.5 PV in the secondary will be open. And at just under WOT and 8" of vacuum the 6.5 will remain open.
    Theoretically, this should allow me to jet more accordingly to 'upper RPM cruising', not dump unnecessary fuel, and still be 'safe' at WOT and just below.
    Hopefully...slightly better fuel economy and no torched pistons!
    <img src=http://www.performanceboats.com/gallery/data/500/medium/06-30-11_1234.jpg border=0 alt= />

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    gn7
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    Quote Originally Posted by HammerDown View Post

    Hopefully...slightly better fuel economy and no torched pistons!:
    There is a balance when trying for every MPG.
    Every engine combo/boat is different. Cam, manifold single or dual plane, engine size verses carb(s) size, boat size, and drive type all determine if a secondary PV is of any use.
    Big cam, with a dual 850s on a tunnel ram, and the secondary PV is virtually guaranteed to be a waste of time.



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    I went and ran around all day and never hooked the vacuum gauge up forgot... I dont nessicarily think that a pv in the secondary side is a must heck holley dont even put them in there hp carbs untill the 830 so there must not be a big need for one

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    gn7
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    Quote Originally Posted by glastornjet73 View Post
    I went and ran around all day and never hooked the vacuum gauge up forgot... I dont nessicarily think that a pv in the secondary side is a must heck holley dont even put them in there hp carbs untill the 830 so there must not be a big need for one
    I don't what you mean by "until" the 830. Holley only put secondary PVs in some marine applications as far as I know. And I am not all that sure why they felt that was useful on a non application specific, purpose built carb.



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    Quote Originally Posted by gn7 View Post
    Quote Originally Posted by glastornjet73 View Post
    I went and ran around all day and never hooked the vacuum gauge up forgot... I dont nessicarily think that a pv in the secondary side is a must heck holley dont even put them in there hp carbs untill the 830 so there must not be a big need for one
    I don't what you mean by "until" the 830. Holley only put secondary PVs in some marine applications as far as I know. And I am not all that sure why they felt that was useful on a non application specific, purpose built carb.
    Sorry probly not the best word i could have picked there ( just a dumb old redneck from southern il) "until" meaning everything smaller than the 830hp series carbs did not have piwer valves nor has any dominator ever had a power valve if memory serves me correctly power valves deff serve there purpose but if you are goin for all out top end hp i feel the best way to acheve that is to do away with them and jet for wot and screw the rest of the part throttle tuning if its a little rich so be it but for over all power exonomy and longevity power valves are deff a great thing the more i think about it it i think i mighy keep the rear and bring em both in just before wot and start jetting from there

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