air pump or fuel pump?

Yours is not a pressurized tank in 78.

The pressurized tank is from the sixty's.

The pressurized tank had two lines running to it.

One line was the vapour line from the crankcase and the other fed the fuel up to the carb.

If you have only one line from the tank it is the newer suction style which has a fuel pump on the side of the engine.

It's been awhile since I fixed boat motors . You have a bulb in the fuel line I think don't you ? When you pump the bulb it simply pumps fuel to the fuel pump , follow the line from the bulb and it ends at the pump I believe , the pump is probably actuated by crank case air pressure pulses , which in turn is translated into a pumping action that makes the fuel flow to the carbs . the fuel tank is not pressureized , that could lead to uncontrolled fuel flow if a hose broke , it is sucked out just like a coke and a straw , then blown out your nose to the carbs .

The A.I.R. pump stands for air injection reaction. It's an electric air pump that pumps outside air into the exhaust stream at cold startup. The extra air helps oxidize the rich mixture you need to start a cold engine. The extra air also helps fire off the catalytic converter to get it up to operating temp faster. So yes, it is for emissions. And yes, it has a reasonably high failure rate.

If you're running oil and gas mix, no fuel pump, 2 cycle, no pump.