Re: how can you tell if you have a 4 stroke or a 2?
Eric, as mentioned, the number of cylinders and/or spark plugs has nothing to do with whether a motor is 2-stroke or 4-stroke.
A 4-stroke motor (sometimes also called a 4-cycle motor) has 4 distinct compnents to each power pulse. Those are the intake stroke, the compression stroke, the power stroke and the exhaust stroke. All of these involve the piston moving up an down in the cylinder. On the intake stroke, the intake valve is opened and, as the piston moves forward, into the cylinder bore, fuel/air mixture is pulled into the cylinder. As the cylinder begins to move backwards, toward the cylinder head (compression stroke), the intake valve is closed and the fuel/air mixture is compressed. At a certain number of "degrees before top dead center," the spark plug fires and the piston is forced forward by the expanding gases. This is the power stroke. The final phase in the sequence is the exhaust stroke, when the piston moves back towards the cylinder head again, this time with the exhaust valve open. In a 4-2troke motor, the spark plug fires every other time the piston reaches a certain point in the "upstroke."
In a 2-stroke engine, the intake stroke and the compression stroke are combined and the power stroke and exhaust stroke are combiined. There are no valves in the motor, which has intake and exhaust ports cut into the sides of the cylinders instead. In this type of motor, the spark plug fires every time the piston reaches a certain point in the "upstroke."
One of the easiest ways to tell the difference between the two motors is to just listen to them. 2-stroke motors usually sound louder and have a higher pitch sound than the 4-strokes do. You may also be able to tell by the size of the motor - for a given horesepower rating, 4-stroke engines tend to be larger and heavier. This is due to the added parts associated with the valve train in the 4-stroke.
As was mentioned, you might do well to buy an engine service manual for your motor. I also recommend reading a bit about basic outboard motor design. The more you know about outboard motors in general, and your motor specifically, the easier it will be to operate it correctly.