Re: need some info
That serial number predates the production of 200hp Mercs... So I will assume (unless you tell me otherwise) that it is a model 200, a 20hp, 2 cylinder engine... Then the serial number indicates the engine is 1976.
Prop... The '11P' indicates the prop has a pitch of 11 inches (that was the standard prop supplied with the engine in 1976.) So any 3 blade prop with an 11 inch pitch (of similar diameter and the same shaft size and spline count) will be right.... You should be able to go to any Merc dealer and ask for a prop of that size....
Fuel mixture is 50:1, use a good quality 2 stroke oil with a TC-W3 rating.
Chris.........