Re: Starting "new" 1986 Evinrude 6 hp
I think I'd fill with fresh fuel, treat as new and solve any problems if you find them.
BUT a new pump impeller would be more than sensible. That's mentioned in High Trims link I feel sure.
Also note it should run on 50:1 even if the manual or decals say 100:1!
Standard plug recommended is now QL77JC4 and the gap now recommended is 0.030" ( but i only discovered this recently and still have the original QL77J4 in mine and still gapped at 0.040")
For continuous high speed operation they still recommend the surface gapped QL78V it seems.
The only problem I have had with mine is that the grommet at the top of the water tube gets squeezed over the top of the tube by corrosion until it cuts off the water flow.