Not a lot to go on here Norm, could be lots of things.

How old is the engine - years?
Hours?
Did you get a log book with it?
Serviced regularly?
When was last carb balance performed?
Has the engine ever been torn down and inspected? How long ago - hours?
Has the gearbox ever been inspected? How long ago - hours?

Is this the same 2 blade prop you had severe vibration with on your other aircraft?

What are the props you are referring to now?

Have either prop/engine/gearbox combinations been dynamically balanced?

Greg