I put a slip on exhaust on my cbr600f over the weekend, the first time i rode it afterwards it was fine but it is having a problem getting past about 2 or 3k revs, it feels a bit juddery/hesitant and wont accelerate, once it gets to a certain point the revs shoot up and there is no problem at all once your moving. Im not sure if the ecu on the bike can adapt to a different exhaust and it may fix it itself, id imagine its old enough (2003) that it wouldn’t.