See below, in
bold text, source =
http://newboatbuilders.com/pages/fuel.html
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FUEL SYSTEMS
[red]Warning: I am only going to very briefly cover the basics here. There is much much more! Contact ABYC and the Coast Guard to get the latest standards for fuel systems.[/red]
The Federal fuel system standards apply to:
Boats with permanently installed inboard gasoline engines for:
Propulsion, Generators, Auxiliary Equipment
This does not apply to:
-Outboards, Portable Equipment
Having said that, that is, the fuel system regulations don't apply to outboard powered boats, don't take that too seriously. [/b]The industry follows the ABYC standards, which are tougher than the Federal standards. ABYC fuel system standards apply to outboard powered boats with permanently installed fuel systems. [/b]If you ever get dragged into court, that's what the complainants attorney will ask you. "Do you meet ABYC standards"? So follow the Federal rules for inboards too, even if you're making an outboard powered boat, unless you intend to use only portable fuel tanks.
FUEL SYSTEMS:
Vents: Fuel tanks have to be vented. The vent itself has to either have a flame arrestor that can be cleaned, or be designed in a way to prevent a flame front from igniting the fumes in the vent. There are a lot of different brands of fuel vent fittings on the market that accomplish this.
This vent must not allow gasoline that might spill from the vent when someone overfills the tank, to spill into the boat. Catch 22. It is also illegal to spill fuel into the environment. So, think about it. There are several manufacturers that make combined fuel fill and vent fittings that do just that.
Fuel Pumps: Fuel pumps cannot leak into the boat, so if you have an engine that uses a mechanical fuel pump it has to be a double diaphragm pump or have some other means to keep the fuel from leaking into the boat
Electric fuel pumps can only operate when the engine is running.
Carburetors: Carburetors must be of a marine type. Again this is because you don't want fuel spilling into the boat. So, if the carburetor floods or the float sticks it must be designed to keep the excess fuel from flowing out of the top of the carburetor through a vent or other opening. Use only a marine type carburetor! Yes, they cost more. Yes, they look just like an automotive carburetor. But, they are different inside, and the difference can save your life.
Fuel Hose: When fuel hose is used it must be either USCG Type A1, USCG Type A2, USCG Type B1 or USCG type B2. Where you use it determines what type you use.
From the fuel inlet on the engine (usually the fuel pump) to the carburetor you must use Type A1 or A2.
Each fuel vent line or fill line must be USCG Type A1 or A2 and the line from the fuel tank to the engine inlet must be type A1 or A2;
UNLESS:
if no more than five ounces of fuel is discharged in 2 1/2 minutes when:
(A) The hose is severed at the point where maximum drainage of fuel would occur,
(B) The boat is in its static floating position, and
(C) The fuel system is filled to the capacity market on the tank label.
Then you may use Type B1 or B2.
As a practical matter, few boatbuilders want to have to stock two types of hose, so most buy only Type A1 and use it everywhere. This is fine. Just be sure that you put in your owner's manual that the hose from the fuel pump to the carburetor and the vent and fill hose must be TYPE A1 or A2.
So whats the difference between A1, A2, B1, and B2? First the difference between A and B. A hose has to pass the 2 ˝ minute fire test, B does not. The theory is the A is under more pressure than B, and being on the engine is exposed to more danger of fire than B. Since B is betwen the pump and the tank, if a leak occurs, the pressure rapidly drops to zero and the pump just sucks air, stopping the engine. Fuel doesn't get sprayed all over the place. With Type A, since it is between the fuel pump and the carburetor, it is under pressure and there is the potential that fuel will be sprayed around.
The difference between Type 1 and 2 is the permeability. All hose allows a small amount of vapor to pass out through the wall of the hose. The more permeable the hose is, the more vapor passes through. A1 and B1 pass much less than A2 and B2. About 1/3 as much. The Coast Guard Sets the standard for the amount that is allowed.
You do not have to use hose! You can use metallic lines. Some manufacturers do. For example, Mercury Marine inboard engines come with steel fuel line from the fuel pump to the carburetor.
[red]
Mettalic fuel Lines:[/red] If you use metallic fuel lines, the ones that run from the fuel tank to the fuel inlet on the engine must be one of the following; seamless annealed copper, nickel-copper, or copper-nickel. From the fuel pump to the carburetor they can be any metal you want to use. Beware. You could set up a galvanic couple and the tube will be eaten away like powder. Choose carefully if you use metal fuel line from the pump to the carburetor. 
Carb. Plumbing ? 
