Safer carburettor in a box?

Discussion in 'Inboards' started by tom kane, May 22, 2014.

  1. tom kane
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    tom kane Senior Member

    If a carburetor floods or fuel leaks on an inboard gasoline motor where does that fuel go? Maybe into the bilges where it is not wanted so why not seal the carby from the bilges so that can not happen. If it is fitted into a container the fuel stays there and can be automatically directly fed safely into the induction manifold by evaporation and manifold low pressure.Good idea or bad?

    It is not quiet as simple as that but it can be easily done very cheaply.
     

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  2. Petros
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    Petros Senior Member

    usually the term "flooding" the engine means it has too much fuel inside the intake manifold and combustion chambers. if this happens there is no risk to the boat, it will only make it hard to start until you either blow the excess fuel out the exhaust or allow it some time to evaporate.

    if you have leaking outside the carb that is usually due to faulty fuel lines or connectors. If the carb leaks fuel out the vents it normally goes down the intake, but can spill out on to the engine. that means usually eithe the float or needle valve are defective and needs to be repaired or replaced. putting the carb in a box will not prevent this, but will allow a lot of fuel to accumulate before you know you have a problem.

    also, the carburator has to stay cool or you risk vapor lock. A box sitting on an engine will get hot and not allow much cooling to the carb, this would be a really bad idea.

    The most important thing is to mainain the fuel system so the lines, filters, and all connectors do not leak. It might be possible to run all of that in a large PVC pipe, than can drain overboard, but it will be hard to know when you have a leak and it will not be easy to inspect the condition of the line and connectors.

    I would think keeping the fuel system simple, and easy to access/inspect would prevent more leaks than a box or other means of containing leaking or loose fuel.

    I do not know if they exist, but some means of detecting fuel vapors would be a better early warning system. however, that means another system to test and maintain to make sure it is operating properly.
     
  3. PAR
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    PAR Yacht Designer/Builder

    A marine carb will have bowl vents that dump directly into the venturi(s) through (usually) a "J" tube(s). Other subtle changes to these carps might include internal circuit venting to the throttle bore or bowl, not a pin hole in the carb body, "O" rings on the penetrations (throttle and choke shafts, etc.).

    I agree, keeping the fuel system simple is the better course. Robust lines, attachments, with doubled clamps or better yet mechanical (AN) fittings. Fixing trays and boxes "just in case" seems an incorrect engineering response. You have to assume the end use will receive the appropriate maintenance and upkeep. Other wise you'll end up attempting to design paint that can't be scratched.
     
  4. Ike
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    Ike Senior Member

    This is why marine carburetors are required by law not to leak into the boat. Of course now most new marine engines are fuel injected which for the most part eliminates these issues.
     
  5. powerabout
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    powerabout Senior Member

    except when it does flood you will have a box full of fuel vented to the atmosphere and inlet manifold, back fire and boom
     
  6. tom kane
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    tom kane Senior Member

    Thank`s for all of that input and opinions and I think you have all illustrated all the reasons why a gasoline fuel system on an inboard boat is unsafe and needs re-inventing.
    Fuel injection does not solve all problems and can increase them.
    Insulating a carb or fuel lines from the radiant heat of the engine should be an advantage and cool air from out side of the engine compartment is better for the motor.
    Carbs run cool because of temperature drop by evaporation and can freeze.
    Maintenance is not a thing many people know how to do or do well, better to have a fail safe system.
    Gas detectors work only after the problem has happened and then maybe and don`t solve the fault.
    Marine carbs do not stop fuel from finding it`s way into the bilges.
     
  7. PAR
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    PAR Yacht Designer/Builder

    There's absolutely nothing wrong with gas powered craft. Systems and requirements are in place and the 1960's are long past. The old days of boats regularly blowing up are past, though admittedly it still happens, but not because of the carb, but usually because of a lack of maintenance, a leaking fitting, cracked line, etc. This is how fuel gets into the bilge.

    EFI has all but eliminated these issues, plus dramatically improved starting, reliability, durability and maintenance requirements. Fail safe systems are nice, but often not practical or cost effective. This is why EFI is showing up on boats. It's not because they're looking for a safer system, but because they're building to a price point and these new generation of electronically controlled engines, come with EFI systems. They're not going to retro fit each with a carb, no they eat the up front cost of the system and gain reliability and lower maintenance reputations. You can park a 5.7 Mercruiser EFI for 5 years and it'll start with a fresh battery, with little fuss. Try that with a varnished up carb, maybe one with pitted points . . .

    Ford was against hydraulic brakes for a long time, siting initial costs and labor to install. Eventually he had no choice, but to keep up with the competition and because, the mechanical brake parts where becoming harder to find. Personally I think he was an idiot, but he did eventually figure out how to build to a price point, with a few innovations along the way.

    Maybe aircraft should have an extra pair of wings, retracted of course, just in case.
     
  8. powerabout
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    powerabout Senior Member

    years ago in Australia the insurance companies statistics said diesel pleasure craft go up in flames more often than petrol powered ones.
    The issue was huge diesels in small engines rooms and fuel or oil leaks onto hot turbo's and exhausts guarantees a bonfire.
    Spray hot petrol on a red hot turbo and it does not ignite ( add a spark and its a whole other story of course)
     
  9. PAR
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    PAR Yacht Designer/Builder

    A common mistake that people make when trying to design something completely foolproof is, to underestimate the ingenuity of complete fools . . .
     
  10. powerabout
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    powerabout Senior Member

    Par
    you would remember those old K&W ( I think) turbo kits for Mercrusiers, that had a blow thru carb in a box, scary
     
  11. Ike
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    Ike Senior Member

    Amen:

    "Never underestimate the power of human stupidity." R. A. Heinlein.
     
  12. tom kane
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    tom kane Senior Member

    The Auto Industry is constantly trying to make motoring safer by installing anti skid anti lock brakes, lane checking devices and a multitude of other automatic systems.The boating industries need to keep innovation going and not relying on traditional methods especially when we move into more volatile fuels like Hydrogen and gases.

    The only extra part fitted to the fuel system in the image of the old Opel motor is the box surrounding the carb that does what a Marine carb does (it could be a Marine carb).
    The box collects any wet fuel and vapors that is scavenged into the induction along with crankcase and rocker cover vapors so they will not finish up in the bilges.

    The box has a cover through which the twin carb protudes and the carb is fitted with a flash screen and filter. Cool air from outside of the engine box is fed into the carb.

    The principle of isolating the fuel system and fuel storage from the Oxygen in the air in any vehicle should be a good idea.
     
  13. tom kane
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    tom kane Senior Member

    Safer carburettor in box?

    I do not think there is any EFI systems designed for use in boats but they are all
    made for autos without thought for the specific needs of boat safety, cost can not be an excuse.The same thing happened when auto engines were first installed in boats.
    With EFI there is no room for "keep it simple"
     

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  14. PAR
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    From an engineering view point, you wouldn't want a containment box - an after the fact bandaid approach, but rather a "tighter" control at potential sources. Yes, high pressure fuel lines can fail, usually violently, but they are made to a much higher standard in anticipation of this potential, so unless extreme neglect is shown, not an issue.

    It will be unlikely a 50 year old EFI will be "rehabbed" by a backyard restorer, mostly because the parts wouldn't be trustworthy, so they'd be replaced with new, possibly upgraded to a more current system. Those systems that need or require a true restoration will still have the pieces replaced. The '64 fuelly Vette a buddy restored had to go through this, with a fully restored, rebuilt and re-machined assembly. No one in their right mind, installs a well worn fuel line or other part, if they actually care about safety or durability. I just don't see the need for a containment system, for an event that will likely not occur, nor one that has shown a predominance of happening regularly.

    Fresh air supplies have been used regularly for many generations on marine and automotive applications, all showing their value. I have done this to my garden tractor, knowing the benefits. All the automotive manufactures have incorporated cold air systems on their intakes, usually stealing air from a high pressure area ahead of the front wheel or over the radiator top.

    Yes marine EFI's are designed and employed, though you're correct many engine suppliers are simply using an automotive system. This is a price point business decision mainly, as the dedicated marine systems are more costly and not wholly necessary. A primary reason for this is electrical connector technology, used in these (and other) systems. I just replaced all 5 solenoids and the force pump motor in my electronically controlled automatic transmission. All of these pieces live submerged in a bath of hot hydraulic oil, yet maintain separation and connectivity. Those like you would think "just one arc" and it's a problem, but in fact, my transmission had 225,000 miles on it, before I did the solenoids. In fact, the main problem was an external connection on top of the trans, but since the harness needed to be replaced, I did the external, internal harnesses, accumulator springs and solenoids all at the same time, just so I wouldn't have to pull the pan again, any time soon. I can get another 200k from this trans, likely with a new torque converter and possibly a pump, but these are fairly easy to R&R. This is the difference between modern engineering and machining operations and the old school, bang it to shape and have a pan to catch the drips approach, used previously. All the parts on this trans fit very precisely, nothing like what an old 350TH or PowerGlide would show on disassembly. You wouldn't even think about asking for 200k from one of these, without new bands, clutches and other associated parts, but the CNC cut parts and serious engineering used in my 4L80E easily triples it's durability and reliability, comparatively. And this is why we don't see EFI (even the automotive versions) blowing up all over the place, like we did with carb systems in the '60's and '70's. Don't get me wrong they do occasionally burn a boat down, but the reason isn't engineering solutions, but 99% of the time neglect, which is frankly imposable to engineer out of the equation.
     

  15. powerabout
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    powerabout Senior Member

    Tom, they are custom made as from day 1 the uscg said there cannot be a return line, some autos have now followed this.
    dont forget that for merc anyway they had efi on outboards before the inboards.
    these days i see more cars burning on the side of the road than i ever did in the 70's
    I wonder why?
    Cheers
     
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