Today my friend was riding his 2007 Duce, at 70 mile per hour in 6th gear speed decreases additional power applied causes bike to feel like it is flooding which requires downshifting to 5th gear which causes the bike to backfire. Continuing downshifting causes the bike to backfire in each gear, any idea what may be causing this problem?

 

mine did that is a pouring down rain because water was getting in the filter. i would guess it is a fuel issue, maybe bad gas