[Coley]

...wow just ran the number on that fuel mileage (3km's/litre), particularly for a 6 cylinder? (250? or?).....thats about 7-9 mpg....that ain't great for sure. You should be doing way better than that with a 6 cyl.
Some questions for you:
Have you tuned this thing up lately?
Electronic ignition or?
Timing?
Carb condition/adjustment?
compression test?
.....get us some more info Johnny...because you should definitely be well above 7-9mpg.
My two bits.
Coley