I've been following this thread from the beginning because I have a similar issue with my '14. Let me start my saying that my '14, right from when I bought it six months ago (it had 16,500 miles on it), has never run as smoothly as my '11. I know....you will say then why did you buy the '14?. I wanted a "Red" bike with cruise control and a digital dash that I could actually read. But I digress....
Anyway, it has always had a slight hesitation at all speeds. Nothing earth-shattering but just a little annoying. Then about a month ago while on a long trip, one morning a long way from home, I started her up and I almost didn't get it out of the parking lot. When I gave it even a little throttle it wanted to die. It kept that up for the next 30 miles then seemed to go back to its old self of having a slight hesitation for the rest of the day. Over the last month it has gotten progressively worse. Last week I was on another of my three day rides. Every morning it would act out the same, give it some throttle early in the day and it wanted to stop running. Had to give it a lot of gas to even get out of the parking lot of my motel (didn't really know if I was going to make it home).
As usual, 20 or 30 miles down the road it smoothed out once again but this time it acted up on and off the rest of the day. It is a little scary not knowing what bike I will be riding for the day. The part I hated the most is pulling away from a stop with a severe right or left turn then not knowing if it will quit half way through the intersection and leave me on the ground.
I've read this thread through several times as well as other references to similar problems I found on the web. As most of us would have done I looked at the easiest fix first. I tightened down the battery connections...no change. Then someone mentioned the possibility of a blocked tank vent tube so I thought I would investigate that. The inside of the cap was dirty so I make sure that was all dirt free. I also "gently" blew air down into the vent tube and cleaned what I could of the vent in the cap. The next morning I expected to pull out of my driveway with full throttle so I didn't dump it and miraculously it ran like a different bike. I went on a 150 mile ride and no issues except the constant surging that I've always had (that seems to be getting a little worse). I was ecstatic, I didn't have to worry about dumping it at the next stoplight.
Today I took it for a 40 mile ride around the local area with lots of stops and it exhibited none of the terrible cutting out I experienced last week. So I'm cautiously optimistic that the terrible cutting out at acceleration is over with. Now I have to figure out why it doesn't want to run as well as the '11 and seems to be getting more pronounced as I put more miles on it. It now has 33,600 miles on it.