i have a 99 r1 as well and it has been making a popping sound too. it also has 13k miles and the carburators were cleaned this summer. i really only popps as i am comming down from rpm´s above 5 or more. there is some at less rpm´s but its not as noticable. i dont have an answer for you right now but if you have one please let me know and if i find an answer ill let you know. just send me your email address if you want to. thanks, ryan b