ST4S, lowered gearing, performance cans, TFI injection gizmo, lightened flywheel and me behind the handlebars ..... max I've seen is 158 Plymouth to somewhere on the M5 at a "sensible" cruising speed!
Then again, I was getting 145 miles per tank out of it blatting around the mountains in Spain.
As long as there's enough in it to get me to the next fuel stop I'm not that fussy.
If I wanted fuel economy I'd buy a diesel powered Enfield!