I bought my roadking this past May. When I would downshift going downhill it would backfire a little bit. In July I had the stock mufflers altered, ( I know I may catch a little flack for that ), now the backfiring is worse. I had a fuel management system installed and it still backfires the way it did before I had it put on. The bike seems to run perfectly. What all could be causing this? Could leaks elsewhere in the exhaust system do it? BTW it's a 2001 RK.