For economical running, the engine then employs “lean burn control,” which Honda says improved fuel economy over its previous model by 19 percent. In our test, on a Pioneer 180 bay boat, the most fuel-efficient cruise speed was 20.5 mph at 3,500 rpm. We got better than 5.5 mpg at that speed. Pretty sweet. And, at 4,500 rpm and 30 mph, we still got 5.2 mpg for those who enjoy economy at a higher speed.