have you been parking the car in a different place than you used to?
or driving it harder, with more revs?
if you granny it for a long time the exhaust gasses have been travelling slowly through the exhaust system and that allows carbon to settle and collect in the mufflers and pipes, and then if you park the car outside, it gets condensation inside the system and out comes that wet sut when you give her a few revs.
but yeah if thats the case it shouldn't do it all the time, it could be running very rich, i dont know how many oxy sensors the VN's have 1 or 2, maybe swap them with a mates car and see if the performance of the3 car changes, if it gets bettwe yours are stuffed, if it gets worse, your mates are stuffed, if its the same look further, like MAP sensor possibly.
Good luck