noob needs help with mileage

noob needs help with mileage - only 10 MPG!

BillGrissom said
If you have the hydraulic lifters of the 1980, no need to adjust valves, but do verify the lifters aren't gunked up.

solid lifter in all slants from 1960-1980 (us)
hydraulic lifters in slant 1981-1987 (us)
I don't recall when production ended for foreign markets and what valvetrains were used.