You might have a little twist in your forks.
I've had the same problem and it was New. Small vibration at the 40 to 50 mph area. Some at decel to.
I found a "thread" that commented about fork "sticksion"(stick shun) that caused the same effect.
those "threads sugguested(spelled right?)loosening the lower fork mounts, and retightening.
So,,,,,,,,,,,,
I raised the front tire just off the pavement and loosened(is that spelled right?)the lower fork mounts and re-tightened to spec and all was good.
The Thought being that a twisted fork is turning the tire just enough that it is trying to go in any other direction than straight.
Causing the vibration,,,,,,,,,,,,,,HAND
