An outboard motor mounted to a hull of a watercraft includes a V-type engine having right and left cylinder banks positioned in a cowling and having a crankshaft generally vertically disposed when the watercraft is under a running condition. A surge tank is disposed in the cowling. Right and left side long intake conduits and right and left side short intake conduits both connect the surge tank to intake ports of respective right and left banks of cylinders. The associated long intake conduits and short intake conduits can be selectively established depending on information about operational conditions of the hull and/or the outboard motor. The outboard motor includes right and left shut-off valves interchanging the long intake conduits and the short intake conduits. Right and left actuators individually actuate the right and left shut-off valves in accordance with information about operational conditions. A control means individually controls operations of the respective actuators.