yamaha OX66 250 hp

[SEAFARI]

That motor has a sweet spot at 3900-4000 rpm will
burn about 12-14 gph depending on the load. Anything
over that it will drink like a fish.

[eggsuckindog]

I have a 200 EFI Merc and noticed the same thing - my cruise 3400/3600 - at 4000 the motor pitch changes obviously and without really knowing I'm sure the consumption as well. At modest cruise 3400 -3800 I get 2 to 2.5 mpg in flat water, that I have checked well. I would expect similar for that motor.