with respect to the Dell'Orto, i can pretty much second everything that TG Farrell said. i had similar experiences with mine when i finally got around to tuning it - oh, and mine was on a 13B that had seen better days. i got consistent 23-24 mpg on the highway and if i recall, i'd get around 18 in city/local driving. i really miss that Dell.
a 12A on a stock Nikki should at least match that, but should probably do a little better.