Re: old elto
EDIT:
A 3D15E is an Elto Campster 3 hp. 1958. Same 16:1 recommendation.
The only thing I could come up with is that it is a 3 hp Gale Buccaneer, model 3D15B, single cylinder, 1958. Motor was manufactured by the Gale division of OMC.
A 1958 Johnson-Evinrude of that year was a 16:1 mix, so that would be a good bet for a Gale.
If that is what it is.