My box-stock carbureted '87 Samurai would get about 25 mpg in everyday suburban type driving (2wd hubs unlocked).  It seemed like a lot less, though.  I had to put gas in it about every other day because the tank was so small...

I get about 23mpg in my stock 92 sammi although it has a performance air filter on. Would this increase fuel consumption?
Thrashing it certainly would which is what i do most of the time to get the full noise from the air filter!   Just cant resist!