Welcome Bookjunkie! A person after my own heart
A 4 stroke motor means that it has intake & exaust valves and does not require oil mixed into the fuel.
As a rule they are quiet and very dependable. The 2 stroke needs more TLC and can be made to run much faster than the 4 stroke. The avg life for both can excede 10,000 miles, depending on how you take care of them. Kind of like a boyfriend
4 strokes can be made very fast to. 2 stroke = more torque, 4 stroke = more power. Dax & Spookytooth both have some great motors & bikes to choose from. Look at it this way, I can go from Dallas Texas, to L.A. Calli for under 15.00 in gas!