Hesitation, surging and crap mpg.

[Lawrence]

Don't think bad petrol is the case for me, I do a tank in two days (13 litres/day at the moment, ~35mpg :'(), have use several different petrol stations and have even tried super in it.

Swapped the plugs out for the old ones that were removed a couple of months back and there's no change.  The plugs that came out are completely black.

I didn't get this before it started running like total shite so I'm very tempted to swap the original carbs back on.