Thanks for the clarification OAG - my post was quite misleading. It was written with the comment that inspired it in mind, reproduced here:
The 140 tonnes of Jet-A1 contained about 80 tonnes of C, so with 340 tonnes of O2 from the air, we have 420 tonnes of CO2.
In context, my working was correct I think. I take your point about the average ratio of CO2 to fuel being 3.155. Perhaps the appropriate correction to the above statement should be that there is ~120t of C in 140t of fuel, and left the CO2 product alone?
This is all getting quite hair-splitting. I'm off...
O8