Yeah that sounds about right.
My 26cc gas engine with a tuned pipe was sucking the fuel out of the tank quite fast. Sort of like pouring out on the ground kinda fast through a tube. You could watch the fuel level go down while you watched it run at full throttle. And it was running on gasoline too.

It might be worth it to test run the engine on a stand to get a fairly good idea of its fuel consumption. It would help one plan as to how much fuel they need to fly it with.