RE: outboard motor mpg
rocky,
When talking about boats,outboard or inboard engines you need to think of "Gallons per Hour" (GPH) - not - Miles per Gallon(MPG).
GPH is based on at least; speed,trim,load,prop,water,weather conditions(wave and wind action). Those 1st 4 are probably the most critical when talking GPH(assuming your engine is well tuned).