Is my pw50 a 2 stroke?

Could be either, Yamaha made both a 2 and 4 stroke PW50, affectionately known as PeeWee. One way to tell is look for a dip=stick for crankcase oil. No dipstick= 2 stroke. Dipstick means a crankcase with oil. Check your owners manual, if it says to mix oil in gas,= 2 stroke.