Fuel consumption is a direct function of the amount of power being demanded. At 2000 (which is rather low for cruising - 2200 is better - you are using about 16hp and fuel burn is around 1.7l hour. If you use maximum revs the prop will demand close to the full 29hp, so as suggested fuel consumption will nearly double.
You can check your actual consumption by brimming the tank, running 20 hours or so and brimming again.