Usually take a half filled 6 gal tankl, good for 45-50 Km cruises between 1/2 to 3/4 throttle with 1 gal left over at day's end. A newer 2 strokes will probably consume les bit fuel compared to a used one, compression issues in which needs less throtttle. Have you tried using high octane fuels than regular ones and check if mileage increases ?
For me high octane works much better than regular fuels, keeps combustion chambers cleaner and engine more throttle responsive while medium loaded. With fully inflated sib and healthy engine sitting at correct transom heigh will achieve better mileage, same if comparing to car tires better mileage.
Happy Boating
