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Old 08-01-2011, 08:51 AM   #1
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Marine supercharger carburetors?

Hi all,

I need to order a pair of carbs for my blower, at the moment it's running a single 1000cfm. I'm told this can cause issues with leaning out the rear cylinders and I'd be better off with a pair of around 750's.

I've looked on Jegs and Summit where I can find plenty of marine carbs or supercharger carbs, but none for marine superchargers.

Do I need to worry about the marine bit given that they'll be up in open air?
If so, anyone got any suggestions of where I can find some?

Cheers, James

PS. If anyone wants a basically new 1000cfm holley, let me know!
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Old 08-01-2011, 10:55 AM   #2
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It may be stating the obvious but get on the american forums like scream and fly or offshore only, or try a company like teague. Good luck.
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Old 08-01-2011, 11:19 AM   #3
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Hi james try PAW they are in cali and have the carbs you want at a good price
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Old 08-01-2011, 11:26 AM   #4
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Perfomance Automotive Warehouse is wot you are looking for they have the carbs and a ton off other stuff they may be of use to you on your build regards paul
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Old 08-01-2011, 05:50 PM   #5
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Grand. Renegade, I posted on there too but thought I'd ask on both sides of the pond. They seem to rekon I should stick with the single.

Paul - Cheers for that, I'll have a nose through their stuff

James
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Old 09-01-2011, 11:15 AM   #6
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james
we are using Demon(berry grant)http://www.barrygrant.com/ carbs on our drag race cars, there is also a blower calibration available.
demon carbs are way more accurate and better to tune then a holly carb and race stuff.

http://www.jegs.com/p/Barry-Grant/De...55476/10002/-1

what blower do you run gm type 671 674 or b&M

bds has also good blower service and well known in blowers since 30 years
http://www.blowerdriveservice.com/

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Old 08-02-2011, 07:35 AM   #7
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What size supercharger, engine, boat, it's weight and type of drive to start with. I'll explain why I need this info in the response. Thanks.
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Old 08-02-2011, 08:17 AM   #8
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Boat1/Germansaleen

It's a very light and narrow 25ft revenger. Only 6'6" wide and I'd guess it's about 1500kg ready to go, hull seems just under a tonne. It's very 'petite' for it's length!

It's a penta based 502 motor with 8.81:1 compression, standard rectangular port iron heads, stainless marine headers, roller rockers etc.

Blower is a B&M 250 with superchiller.

Drive is currently a Bravo 1, early type but holding up well. I'll upgrade as necessary in the future.

Use is going to be leisure for this year, then mixed leisure and racing next year.

Boat1, are you the same Boat1 as on OSO?

Cheers, James
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Old 08-02-2011, 03:26 PM   #9
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Thanks for the info, yes the same Boat1. Marine carburetors are not significantly different than automotive, they have a J-tube bowl vent and some seals on the throttle blade shaft to prevent raw fuel from from leaking out the shaft, these are, in my opinion, the only real important differences. For a B&M 250 supercharger I would not spend the money on dual carburetors. I have done quite a few and the dominator carburetor will provide all the air flow you need for a 502 base, in fact it is easier to maintain idle adjustment with the single carburetor. If your current carb does not have j-tube vents, they can be installed. Your application is fairly light, that is helpful. Most carburetor supercharged application go very lean when trying to get on plane for extended times in heavy boats. The best way to correct this is to "boost reference" the carburetor. This is a modification to the metering block the show the power valve the manifold pressure below the supercharger and signals the power valve accordingly. During part throttle loading, "Trying to get on plane without breaking the drive" there may be a significant vacuum under the carburetor due to part throttle and the supercharger trying to suck air, but in the intake manifold you may have low vacuum or slight boost, a condition that would signal a power valve to open and add fuel. Boost referencing will show the carburetor what the engine really needs from the power valve, based on load. A power valve adds the equvalent of 8-10 jet sizes of fuel when open. If you do not have a mechanic that can boost reference the carburetor, a safe approach is to install high flow, 10.5 power valves. This will open the valves sooner and add fuel under load. This is the most important first step in setting up the carburetor. Tell me what your experience level is with carburetors. Do you know the purpose of air bleeds, have you changed the accellerator pumps to 50 cc units, do you know where the transition slot is, have you fully dis-assembled a 4500 series carburetor, is it a two circuit or three curcuit, do you know the accellerator pump ramps are adjustable? Your comments about the single carburetor loading fuel to the rear cylinders is not caused by the single carb, the B&M blowers are 2 lobe style rotors, that is the main reason for the fuel unbalance and it is a function of the blower not the carburetor. Bottom line carbs are great because they are so adjustable to a knowledgable person, but carbs can be a headache because they are so adjustable and lack of knowledge can really get them to poorly function. What camshaft is in the engine? To take full advantage of the supercharger, you must upgrade the camshaft. Lets try and finish this conversation first before we address the camshaft. Good Luck.
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Old 08-02-2011, 04:24 PM   #10
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James give John Kaiserman at Express engines in Florida a call on 001 386 734 9302 make sure you have the build spec for your engine to hand because he will want to know what pistons,cam,comp ratio etc you are using,this mans advice could save you a lot of heartache and money.
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Old 08-02-2011, 09:11 PM   #11
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Oh and tell him i said to call him.
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Old 08-02-2011, 10:39 PM   #12
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Gordon - I'll give him a call. I need to get a spare sec to speak to the builder anyhoo so I'll get the engine specs while I'm there.

Boat1 - Thanks for the advice. My knowlege of this type of carb is limited but I pick things up very quickly anyway. I'll get the nembers off the side of the carb to get it's spec and dismantle it to see what jets, valves etc are currently fitted, hopefully we can go from there. My engine builder is looking into camshafts anyway as my old one has had it!

Cheers, James
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Old 09-02-2011, 03:52 PM   #13
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You should trust your engine builder. I would be happy to provide specs that I have used, and the power it made. If you want any help with the carb let me know. Good luck with your project.
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