When I owned my first Mark I Mini (a '62 850) I had problems with that tiny fuel gauge inside the speedometer assembly. It was inaccurate at the low and high ends (though only the low end concerned me). I finally built up the courage to get into this antique gauge in the center pod and opened it up (by, as I recall, gently prying off the metal cover over the fuel gauge section). Inside, there are 2 electromagnets that can be very gingerly repositioned (but one must be very careful with some extremely delicate wires). It worked and I ended up with an accurate fuel gauge! I hasten to add, though, that all this presumes a good, working sender unit (since all this is a function of voltages, and the sender is basically a variable resister). Anyway, in the process I drew up a little wiring diagram that shows this, which I just found the other day... thought I'd leave it here if needed.