"Diego" wrote
reduce to a very slow speed when moving around the
islands in order to conserve fuel and increase my range.

I once made a 50 mile round trip with a Merc 165 at idle and occasionally
just a tick over. Maybe 1000 RPM during the periods I was hurrying. No
problems at all with the 30 year-old carbureted breaker point engine. Took
about 12 hours and used only a little less fuel than the same trip at a
moderate planing cruise. At the time I was less interested in miles than I
was in time-on-water per gallon, if you know what I mean.