My s2 was running great until 2 days ago then all of a sudden its missfiring and overfuelling, took it to my m8 james at woodford garage to check the fuelling (again) 12.5%!!!! and for some reason it will not adjust but we managed to get it down to around 7-8% but it didnt cure missfire have driven it home very carefully with it popping and banging and missing but now it wont idle and it seems better up the rev range from about 50mph onwards, has anyone any ideas as to what the problem is??? I am thinking metering head or the little black unit on the side of it is knackered am i right??? thanks in advance for any help