For a two stroke they way to work it out is.....
This gives you consumption at max RPM, you take the HP of the engine and divide by a third,
so 135hp is going to use approx 45 litres of fuel per hour at max RPM.
For a 4 stroke you take off about a third again so a 135 four stroke will use approximatly 30 litres an hour at max RPM.
Hope this helps.