Engine year

[sogood28hp]

Hello all from a newbie. I recently bought a 16ft Microplus with a 28hp Yamaha outboard. I am trying to identify the engines year of manufacture. I have the serial number etc. (but not with me at the moment) and would like to get an owners manual to carry out any repairs and maintenance. I do my own motor maintenance etc. so I dont worry in that regard. But it would be useful to know what I'm dealing with. As an aside, the sticker on the engine sys the oil/petrol ratio is 100:1, but I have read that 50:1 is more preferred. Any thoughts?

Many thanks.

[boats.net]

We don't have any information on that model, a 28hp was never sold here in the US.