Just worked out a spot MPG for the last tank of fuel, it came out at 29mpg for the last 137 miles, so it looks like advancing the timing a bit has had the desired effect.
On a different note, Bitsa let me down yesterday for the first time since the rebuilt "new" engine went in - the battery was flat as a pancake, and she refused to start. I suspect that the CB had been draining the battery, despite being switched off, as it had a permanent live feed. I've disconnected it for the short term, longer term plan is to sort it with a key switched live.
I hope its the CB, if not it means yet another dead 16ACR (I've lost count how many have gone bang now, but I know its depressing). If I have another one go, I'll try and replace it with a A127 off a disco tdi.
As I type
9 years ago