What is the cbr 125 2004 original jet size?

Having trouble with my cbr125 not been able to get past 50-55mph. It seems to have a lack of top end power cleaned all the carb out and replaced plug. Just wondering if the main jet may of been changed as there is a sports exhaust on there and perhaps the last owner made a mess of it? Or if theres any other possible causes? Im borrow a compression tester tomorrow off a friend to check compression. Cheers