If it looks like a duck
and quacks like a duck, it must be a duck.
Right? Well, maybe. Carburetors are carburetors, but only marine
carburetors should be used on boats. It's true that marine carburetors
as regular automotive carburetors but then each took divergent paths.
have certain modifications that make them
uniquely adaptable and legal for marine usage. "Legal" meaning that it
the ability to pass the U.S. Coast Guard test for marine carburetors.
Folks, I'm not talking about Paris Island here, either. The main
that a marine carburetor must meet (as set down by the U.S. Coast Guard)
is that if the carburetor should "flood" only .5cc of fuel is allowed to
escape in a period of 30 seconds. There's also a "backfire" test which
confirms the ability of carburetors/flame arrestor combination to
backfire. For this reason a gasket is not used between the carburetor
air horn flange and the flame arrestor. It's possible that this gasket
become saturated with fuel (if the carburetor should flood) and become a
potential fire source as a result.
The primary areas of a
carburetor that require some sort of
modification to meet these requirements include the fuel bowl vent tubes
shafts. The vent tubes of a marine carburetor are bent inwards so that
the tube looks like an inverted "J". These tubes oftentimes are referred
as "J" tubes, as a result. The reason for bending the tubes inward is
if flooding should occur, the fuel that would normally come out of the
fuel bowl vent tube is rerouted back into the carburetor.
Throttle shafts also
get special machining attention. Shafts are
"grooved" and "slabbed" to prevent fuel from exiting out the throttle
flooding should occur. When a carburetor floods fuel will end up
the throttle plates. A non-marine carburetor will allow this fuel to
of the throttle shaft ends and onto the manifold. This is not allowed on
a marine carburetor because normally the engine is situated in an
enclosed bilge where potentially deadly gasoline fuel fumes can
Throttle shafts that are "grooved" and "slabbed" channel the flooded
safely down into the intake manifold. With no raw fuel allowed to puddle
the manifold outside the carburetor, there is no chance of deadly fuel
to accumulate in the bilge and no chance of explosion or fire.
For these reasons an
automotive carburetor should NEVER be used in
a marine application.
For more information:
Barry Grant Demon Carburetors
Hardin Marine (Carb / Intake Kits)