Are you saying you get 15-17.5 in a carbed 1FZ troopy going 75-85mph???
Hello,
You can have that mileage on a 1FZ-FE on highway driving. Not that much on the 1FZ-F; however, the carburetor does have a "high load" circuit that adjusts the mixture to the lean side under conditions such as high speed.
Anyway, the 1FZ is a fun engine to drive.
Juan