Mike,

The first thing I'd do is get your speedo calibrated--it's way off, even
given the lax standards for the 1984 models (IIRC Bentley gives a max of 7%
optimistic for the early part of that year.) If you're really 12% off,
there's something out of whack, and how can you check how many miles you've
driven on a tank with that kind of inaccuracy?

If it's any consolation, I got 12.12 MPG from a recent fill-up. Ok, all
around town, surface streets, uphill downhill, stopping and starting, etc.,
but still--that's just the nature of the beast. The fill-up after that (80%
freeway, AC on, 65 mph) yielded 17.35.  At best, under ideal conditions, my
'84 gets 21. But that's rare. These numbers probably seem more appalling to
us than they did in the early 1980's.

Geza