Re: 1984 Mercury 20 hp blue band whats your experience???
I'm thinking that an '84 was a brown band, not a blue band. Is the shift in the handle or on the side of the motor? If in the handle, you should be sure to idle all the way down before shifting and shift it quick to avoid boogering up the clutch dog and having reverse gear go out. Other than the lousy plastic connectors on the shifting stuff, and the shift in the handle itself, they're good motors. $600 isn't bad if it's in good shape.
GOod luck and I hope you got a good one,
JBJ