Re: 1967 era evinrude 40 hp big twin
The 1967 Bigtwin is a simple, solid and reliable motor. It has a mechanical shift that doesn't need the rare & expensive electrical wiring harnesses & pushbutton remote control that the Lark uses. A single carb keeps it simple & understressed. It uses the double layer midsection often referred to as the "Super Quiet" lower unit. Iit also comes with a superior cooling system that keeps water at the optimum operating temp due to the thermostat and recirculation within the midsection (as compared to the 33 and 1971+ 40s).
They are not an especially fast motor but will push a heavy boat quite well. Expect anywhere from 22 - 35 mph, depending on the boat & prop.
Fuel Usage rule of thumb: 10 h.p. = 1 g.p.h.