Oh right thats why I wasen't sure as they were avaliable with both, I wasen't sure if you meant the carb had been changed but scrap that as you say it's never been off.

Also noticed you mentioned exhaust, whilst obviously it could make a difference, I doubt it's going to effect your fuelling, the case could be different however it it were a modern setup, i.e. Closed loop as more oxygen will be present.

Martin