Backfiring can be caused by an air leak from either the exhaust or intake system.
I'd always thought that "yank" at 50mph was the transmission switching off and locking to direct drive when in automatic. I've never encountered it when riding in manual mode, even leaving in "6th" and crossing over 50mph.
THANK YOU for your research!! (We can put THIS to bed NOW!)Going back to my history and the DN-01, I think I was one of the first that reported the obvious 'bump' at 80km/hr (roughly 50m/h). At the time, back in 2010, I took my bike to a Honda Power House dealer - where I had purchased the bike. The tech and I must have put on another 100 km running up and down the road in front of the store with an analyser hooked up to the bike. He assured me that there was nothing wrong, and what we were experiencing was the 'locking of the transmission' when it adjust from constant variable - to a direct drive in top gear. There was no noticeable change in the fuel consumption registered on his devices.