is it that importantto run a marine carb? if I cant find my holley DP750, I am going to buy a new one, unless some of you guys have one you could sell me, that would be awsome !!
I need to check with my mechanic, but to the best of my knowledge, the marine carb is built so as to not overflow into your bilge area and possibly cause an explosion (critical on enclosed compartments). I know I would definitely go marine, just to help insure everyones safety.
A good carb for your motor is the holly 9022 dual feed double pumper with mechanical secondaries. http://free.***boat.net/ubb/biggrin.gif
It is especially important when you have a closed engine compartment, but when you are running an open one, like yourself the issue becomes less dangerous. I believe the extent of the "marinizing" is to extend the float bowl vents up and back over into the carb so if they do overflow (stuck needle valve) they go back into the carb instead of on your manifold.
I ran a non-marine carb on my old boat with great success. I just JB Welded some brake line of the right diameter I think it was 5/16 into the vent tubes and had already bent it into the right shape. Worked great!
not needed on your boat just fo with the holley 750 dp should be set up well for your boat maybe a minor jet change but you probably wont notice it.
This info is direct from the CPPerformance catalog. I am sure you can find it at other sources as well.
A marine carb has one principle requirement that makes it different from an automobile carb.
The is a USCG test requirement that if the carb floods, only 0.5 cc of fuel can escape within 30 seconds.
1/2 of a cubic centimeter is not much fuel. Close to the equivalent of a couple of drops from a medicine dropper.
How this requirement is met is two fold.
First, J-tubes dump fuel back into the throat of the carb.
Second, no gasket is used which can saturate with fuel and release vapor.
Third, the butterfly shafts are "grooved" and "slabbed". This prevents fuel that puddles on the throttle plates from seeping past the ends of the throttle shafts. Rather the fuel is channeled into the manifold.
So, there is a difference between the two types. And there is a cost difference. I think a list 9022 (800 DP) can be had for around $500. I haven't bought a standard carb in years, but I'd imagine that a list 3310 or a 4150/800DP for a car is still 300 and up.
If you have a closed engine compartment, in my mind, there is no question. Safety is first. If you ever have a fire or explosion and file an insurance claim, my guess is one of the first things that will be looked at is the carb. I wouldn't want to be on the wrong side of a decision that was made earlier that affects payment on a claim
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the above is my new carb from BIGS. There is no doubt in my mind that I will never use a carb built by anyone but BIGS. They set the carb up for your application based on what you have in your engine. Here's an article I originally found that turned me on to them. Their contact info is at the bottom of the article.
Believe it or not, this was a nearly ten year old Holley 650 double pumper. With a complete rebuild and tune from BIGS Performance, it performs better than a new carburetor.
The BIGS treatment includes a full disassembly and cleaning, followed by milling the base, body, and metering block surfaces to ensure a leak free gasket seal. The throttle shafts are removed and bushings installed in the passage to eliminate fuel leakage. Finally custom tuning and enhancements are made as required to match the carburetor. to the customer's engine combination. Since our engine is used mainly at the drag strip, the modifications were based on increasing performance rather than fuel economy.
So you've just finished bolting up that brand new engine. A freshly built shortblock, shiny aluminum heads, a hot cam, full-length headers, and a new intake. What are you going to put on top of it? Probably the same, tired and old Holley 650 you've been running for the past five years? If this scenario sounds all too familiar, don't sweat it you're not alone. We all like the latest, bright and shiny go-fast parts, but when it comes to shelling out several hundred dollars on a new carb, most of us can't justify the expense, especially when the significant other knows how much you've already spent on your project.
Fortunately there is an option that is better than new, but doesn't cost as much. A professional rebuild. We're not talking about picking up a $20 a gasket kit, but rather a complete teardown, blueprinting, and recalibrating to achieve maximum performance, or fuel economy, depending on your exact requirements.
What you end up with is a carburetor that performs better than a new one, because assembly line irregularities are fixed and the carb is tuned to your engine, rather than a "out of the box" calibration.
Here's what we started with; our trusty, but used and abused, Holley 650 cfm double pumper. We bought it from a classified ad several years ago. It's a standard 4150 model, part number 4777.
We recently had an opportunity to renew our Holley 650cfm double pumper that had served us well for nearly six years, and in fact had served someone else for a few years before that.
After building up a new motor we noticed our 650 simply wasn't performing the way it should. The idle screws seemed to be less responsive and the throttle shafts leaked a little fuel. Throttle response off idle and cruise was also not what we'd expect from a fresh engine. Knowing we were way over budget as it was, a brand new carb was out of the question.
We tried rebuilding the carb using a Holley rebuild kit, but the results were mediocre; we fixed some of the leaks, but the carb still felt sluggish. A Holley rebuild kit is probably a good idea every ten-fifteen thousand miles, or once a year, but on a neglected carb like ours, it really demanded more work.
A fellow racer suggested we contact BIGS Performance, a carburetor shop in Wisconsin. BIGS has over 25 years experience rebuilding and customizing Holley's, from daily drivers to circle track engines. We called up BIGS and were surprised to talk directly with owner Lynn Bignell. Lynn spent a good half-hour with us discussing our carb, its problems, and what we wanted to achieve in terms of performance and fuel economy. Lynn and his son Jesse explained to us their procedure of complete disassembly, checking and milling flat each mating surface, correcting and modifying the fuel delivery passages, and other "secret" modifications and calibrations specific to our engine combination (in this case a naturally aspirated, 302 which spends the majority of it's time at the drag strip.)
The total cost for a BIGS rebuild starts at about $150, depending on the level of modifications, but nevertheless a considerable savings over a comparable Holley or Barry Grant performance carburetor. By the way, we didn't tell them until after the conversation that this was a magazine project, so the personal attention we got is definitely standard practice at BIGS.
Here is a general idea of the work BIGS performs during a typical carburetor rebuild and tuning. We'll cover some of these in detail.
Complete disassembly
Thorough cleaning to remove varnish, dirt and corrosion
Check and modify circuits for correct size
Check and clear any casting obstructions
Check and correct surfaces for flatness
Includes float bowl, metering plate, air bleed, throttle
shaft, and boosters to meet or exceed factory
specifications
Remove all metering block brass plugs and clear fuel
well of factory casting
Check air bleeds and adjust if necessary
Change fuel emulsion signal for even fuel flow and
distribution
Rebuilding and Tuning
Over the course of a several days BIGS performed their "magic", meticulously going through every piece of our carburetor, just as they would do with a carburetor for a restoration project, or for a high-rpm oval track motor. We were stunned at just how different the carb looked when BIGS got through with it. Our grimy and sooty carb was now powder coated in brilliant gray. The choke horn that we had crudely hacked off had been milled completely flat, as had the base plate, body, and jet blocks.
At first glance we could tell BIGS had modified the fuel and air bleeds. Upon removing the fuel bowls, we could also tell the numerous passages had been cleaned out, deburred and resized where necessary.
Of course we prodded BIGS to reveal all the intricate details of what all they had done to the carburetor, but owner Lynn Bignell politely told us to "back off!" I guess you can't expect a gourmet cook to reveal his secret recipes!
Although BIGS wouldn't reveal all their secrets, we could spot a few modifications without much disassembly. In the higher-flowing downleg venturis (compared to the venturis in the photo of our original carb.) BIGS also smoothed and contoured the throttle bores, shaved the throttle shaft and installed button head screws, all in the aim to increase airflow through the carb while reducing turbulence and promoting better air-fuel atomization.
To eliminate a lean bog upon launching, BIGS installed jet extensions secondary metering blocks. This prevents the jet from being uncovered as fuel is forced back in the bowl due to the momentum of the vehicle off the line. The screw-in extensions shown are preffered over the "slip on" style that Holley sells, which can fall off the jet.
Also note the use of better sealing and reusable Teflon coated gaskets.
Solid nitrophyl floats were also installed to maintain a consistent fuel level in the bowls,m and to clear the extensions. Stock brass floats can develop small leaks which cause them to fill with fuel and change the fuel level.
We told BIGS that our 9.5:1 302 typically ran a stout solid-roller camshaft and single plane intake, both of which made the idle quality tough to manage.
To remedy this, BIGS made some internal modifications to the carburetor, such as the different idle air bleed orifice shown here. These types of modifications not only require extreme precision, but they require years of knowledge and experience. Unless you know carburetor function inside and out, we recommend you leave it to the pros to make such adjustments.
Continue to the Engine Dyno Testing!
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Contact:
BIGS Performance / Wisconsin Carburetor Service
3228 Pleasant St.
Altoona, WI 54720
715-835-3726
Where I live is a little different from the west coast, not many jets or exposed motors. At my business, we won't even work on a boat if it has an automotive carb, starter, alternater, etc. Years back, my brother-in-law and a friend were out in a stern drive that blew up and burned both of them fairly seriously. I have seen this a few times before and it's pretty scary. Take precautions. What's a life worth?
CP performance sells a kit to make a auto carb marine compliant. Tim
When I had my carb done, C&J installed a "cross tube" instead of the "j-tubes". The cross tube bridges the two "j-tube" fittings with a single tuble, but the tube bridge has a slot on top, so the air gets pulled around it.
This prevents your engine from pulling signal from the "j-tubes", and your float bowls. These guys do alot of big HP carbs, and I guess less vacuum in the bowls is nice...
How much does it help? I don't know...my boat is still slow...
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[This message has been edited by Havasu Hangin' (edited March 15, 2002).]
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