24:1 or 20:1... Please advise.

[55'Fleetwin7.5]

On a 1957 Lark 35. Engine seems to have been well maintained before my tune up - but sat for about 30 years (rope was pulled periodically).
should I run 24:1, 20:1? using 87 octane.

Side note; when using additives like seafoam or the like to refresh cylinders... how do you adjust the ratio to account for the additional volume of fluid?
Thanks

 

[CATransplant]

Re: 24:1 or 20:1... Please advise.

24:1 is fine for that outboard. In fact, that's the recommendation. Use any TCW3 oil you like. Synthetics will smoke a little less, but that's your choice.

As for the Seafoam, etc., you needn't adjust the fuelil ratio.

Nice outboard, and it should serve you well for many more years, once you get it set up just right.