Hi I have a learner restricted comet 650 with a sport exhaust. It tends to backfire occassionally on cold start up and can have a pop/bang that feels like it pushes the fuel tank up. Is this an inherent problem with the learner restrictions in the carbys or a tuning problem that I should get checked out. I have only had the bike a couple of months so am just getting used to its quirks. I have been using optimax fuel... could this be causing my problems?