I have a '13 Beta Evo 4T trials bike that likes to backfire on deceleration, it's pretty annoying. Looking at the parts book, there is no gasket, o-ring or anything else that goes between the exhaust port and the headpipe. The headpipe isnt deformed or damaged, nor is the sleeve at the exhaust port that the headpipe fits over. Does anyone else have the same problem? What did you do to fix it?