How do you tell if is a 4 stroke or a 2 stroke?

Look at exhaust, lots of two strokes have what's called a "fatty pipe" which is bigger, also by the sounds, four strokes are more deep and low pitch when 2s are high pitch and make a popping sound at idle. You can also look for a separate oil tank holding 2 stroke oil, if carb goes to bottom end of engine instead of to the head like in 4 strokes, and if any thing, smell the exhaust, if it smells like oil, smokey it's a 2s (or piece of crap 4s)