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  1. #1
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    Question 2 bbl vs. 4 bbl carb???? Automotive vs. Marine carb????

    I have had my boat for a few years now and I am wondering what the pros and cons are to putting a quadrajet carb on my olds 350 instead of the 2bbl rochester carb that is currently on there. When I purchased the boat it came with an intake manifold for a 4 bbl carb and 3 quadrajet carbs. I haven't done anything with them and I was just thinking about installing the 4 bbl. I have heard many things about this and wondering what peoples take is on it. I have heard that a 4 bbl actually will get better mpg (if you stay out of the gas). On the other hand when into the throttle you will just eat up the gas.

    The next thing that I was told is that a 4 bbl needs to be dialed in more often than a 2 bbl. I don't want have to dial in the carb all the time. I understand you do the beginning of the year tune up and then I would like to forget it and use the boat.

    The next thing will I actually be able to feel the difference in power with the 4 bbl. The gentleman who sold me the boat said he had had it on the motor at one time and didn't see a difference in the performance???

    The final question I have is that I have had a problem with the 2 bbl boiling over. The motor doesn't go above 200 and while running it stays at 160 but if I use the boat for pulling for a long period of time I will start to smell gas fumes and when the hatch is opened you can see steam coming from the carb. Would a 4bbl fix this or is this whole different problem?

    Both these carbs are automotive carbs not marine.....not sure if this makes a difference???

    Thanks
    Ben

  2. #2
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    A 4-barrel carb will improve both top-end speed and acceleration - provided it is jetted & tuned correctly, and appropriately sized (600 cfm is a good size for most mild small blocks). Do NOT use an automotive carb in a boat! It is unsafe and illegal. Doing so could result in an explosion and fire. Marine carbs have features such as curved down air-horns to keep fuel and fuel vapors from escaping into the engine bay. Always use a marine certified carb and flame arrestor (stainless mesh air cleaner). Holley and Barry Grant make some good ones. Your fuel economy will drop, but your fun factor will increase - A good trade-off.
    __________________
    Real Boats Don't Have Propellers!
    -- Rivernut

  3. #3
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    Thank you very much for this information. I have done some research and found that edelbrock has a carb of those standards (600cfm marine). It seems that it is resonable in price also. Have you heard of National Carburetors Comp. This is selling as a reman unit for 250.00 with a lifetime warrenty. Just an option. Thanks for all the info. Would this marine carb take care of my gas vapors and the smell in the boat?

    Thanks and it sounds like something that needs to be addressed asap!

  4. #4
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    Edelbrock makes high quality stuff. I prefer the Holley type carbs for tunability. The Barry Grant carbs are Holley knock-offs with interchangeable parts. I believe the Edlebrock stuff is based on the Carter AFB style carbs. Never used one, but Edlebrock is one of the most proven and trusted companies in the performance aftermarket business. You should also consider installing an aftermarket 4-barrel manifold such as the one I use - an Edlebrock Performer RPM Air-gap intake manifold. Do not run your boat ever if you are smelling gas fumes in the bilge without resolving it. You may want to verify that the engines electrical components (starter and alternator) are marinized with spark / flame arresters.
    __________________
    Real Boats Don't Have Propellers!
    -- Rivernut

  5. #5
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    Quote Originally Posted by BBSPURGEON View Post
    The final question I have is that I have had a problem with the 2 bbl boiling over. The motor doesn't go above 200 and while running it stays at 160 but if I use the boat for pulling for a long period of time I will start to smell gas fumes and when the hatch is opened you can see steam coming from the carb. Would a 4bbl fix this or is this whole different problem?
    Thanks
    Ben
    Ben,

    DO NOT RUN THAT ENGINE ONE MORE MINUTE WITH THAT CARB IN THAT CONDITION!

    You are taking a huge chance of a bilge explosion. I know two people who survived a bilge explosion, and one has years of reconstruction on her leg. You are taking a big risk of injuring or killing yourself, your family and your friends. A fireman once told me that he would rather be injured by any other means than a fire. You can have pain for a lifetime.

    Make sure the next carb has a carb insulator (a thick gasket device that slips between the carb and manifold). Make sue your fuel lines do not run near any hot engine parts.

    Michael

  6. #6
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    Find the source of the vapors look and check if there is a screen on the back of the alternator and check that the starter is a sealed unit. Like said above a bilge fire is preceded by a bang and can be fatal. If caught with auto parts on a boat the fine is stiff. I have found that I got better fuel economy on a 4 barrel than a 2 the primaries seem to be more efficeint until you put your foot in it. Rick

  7. #7
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    Quote Originally Posted by BBSPURGEON View Post
    I have had my boat for a few years now and I am wondering what the pros and cons are to putting a quadrajet carb on my olds 350 instead of the 2bbl rochester carb that is currently on there. When I purchased the boat it came with an intake manifold for a 4 bbl carb and 3 quadrajet carbs. I haven't done anything with them and I was just thinking about installing the 4 bbl. I have heard many things about this and wondering what peoples take is on it. I have heard that a 4 bbl actually will get better mpg (if you stay out of the gas). On the other hand when into the throttle you will just eat up the gas.

    The next thing that I was told is that a 4 bbl needs to be dialed in more often than a 2 bbl. I don't want have to dial in the carb all the time. I understand you do the beginning of the year tune up and then I would like to forget it and use the boat.

    The next thing will I actually be able to feel the difference in power with the 4 bbl. The gentleman who sold me the boat said he had had it on the motor at one time and didn't see a difference in the performance???

    The final question I have is that I have had a problem with the 2 bbl boiling over. The motor doesn't go above 200 and while running it stays at 160 but if I use the boat for pulling for a long period of time I will start to smell gas fumes and when the hatch is opened you can see steam coming from the carb. Would a 4bbl fix this or is this whole different problem?

    Both these carbs are automotive carbs not marine.....not sure if this makes a difference???

    Thanks
    Ben
    I agree with everyone on the 4 barrel, most 2 barrels on V8's are 500 cfm, with a 600 cfm 4 barrel you run on 300 cfm on each with Edelbrock & 4150 Holleys, with a Q-Jet the common carb on 350 will flow 650 - 750 depending on jetting and metering rod choice, so it is around 250 on the front barrels and the rest when the much larger secondary's open. The Edelbrock is a copy of the Carter AFB, this style uses metering rods & jets for tuning both Primary and Secondary which requires either a Tuning Kit or taking it to a tuner who has one. The Quadrajet also uses metering rods & jets for tuning. The Holley use jets on the Primary, and Jets or a Metering Plate on the Secondary depending on whether it has Mechanical (Double Pumper) or Vacuum Secondary's. The Holley is the easiest and the cheapest to tune, in my opinion.
    As far as the boiling over, if the carb seems to be overheating, check the front of the intake manifold under the carb, some had an exhaust passage that ran from side to side to help the carb heat up quicker. This style requies a stailess steel separator to keep the carb from getting too hot. If it has this passage I would drill and tap it for a plug to block it off, or use the stainless steel separator with a Phenolic Resin Spacer to insulate the carb.
    Hope this helps,
    Sid

  8. #8
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    As long as you get a carb with vac. secondary's you should be ok. The secondary's will only open to the amount of air the engine can pull, the Edelbrock AFB style and Q-Jet are very trouble free once setup. As was said blocking the exhaust crossover will keep carb cooler but will need a manual or electric choke. Marine spec carbs are the best way to go. JMO

    Dave
    1980 Cougar 19 tunnel,90 2.4L Bridgeport EFI in middle of restoration.
    1988 BAJA Sunsport 186, 96 225 Pro Max
    79 12' Auminum, 95 Merc 9.9
    RIP Stu
    "So many idiots, so few bullets"

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