Marine carburetors are not highly "specialized" units, but do use different calibrations and offer a few features not found on automotive units.
The vast majority of the Marine units we've had sent in here for rebuilding have been side inlet divorced choke models. ( I've seen a few with electric chokes, but they were really late production and still used the early style castings.) They have all used very small main and idle airbleeds, along with relatively small jets and metering rods. In other words pretty much calibrated like a pre-emissions carburetors from the late 1960's.
They differ distinctly from automotive units in that the baseplate is not equipped with an APT adjustment, and most do not have any idle bypass air passages drilled. The shafts are coated with the green teflon coating found on the later automotive units.
They also have a slashed front vent, with the slash facing back toward the rear of the carburetor. This helps to insure than if/when any flooding would occur, it would go into the engine and not the engine compartment.
The front vacuum fitting in the upper left corner of the main casting is drilled completely thru into the right side main venturi area instead of stopping where it would provide manifold vacuum to the fitting.
For some reason that I will never understand, they continued to use the early large float and early fulcrum position as would be found an any q-jet model prior to 1969 and any Oldmobile carburetor prior to 1975.
The early arrangement is OK, but lacks the leverage on the fuel inlet needle of the later designs. One would think that the later arrangements would be more advantagous in a Marine application considering the environment that a boat operates in?
In any case, don't worry too much about the Coast Guard inspecting your carburetor for compliance. Boarding officers are not trained specifically in carburetor identification. They are trained however in any and all applicable Federal Laws concerning safety equipment. They will be looking for a certified/approved flame arrestor on top of you carburetor, and a working ventilation system in an enclosed engine compartment, plus a working bilge pump or method of emptying the bilges.
In all cases, check the Federal requirements for the length/type of vessel that you own for specifics, and make sure everything is on board that is needed. The Coast Guard also does NOT have juristidiction unless you are operating in a navigable waterway subject to Federal laws/regulations. This includes the Great Lakes, most of the large rivers, some large lakes that have multiple adjoining states, and all ocean waters within the territorial sea.
In any case, I would not use an unmodified automotive carburetor on a Marine application. The venting is there for your safety in case of flooding, etc. The flame arrestor should always be used as well. A marine engine also spends most of it's life in a heavily loaded situation. This requires a calibration that is going to keep plenty of fuel flowing through it to avoid any lean conditions and potential engine damage......Cliff
