I wish it were caused by mods, but its in the bike, right from the factory....
Hers how you'd feel it. Say you in any gear, and above 4500 rpm. I'm not sure 4500 is exactly right. I think the 2011-2013 it was more 4300-4600 rpm, but in the area....
You are over whatever rpm int he 4000's. If you shut the throttle off, then turn back on, theres a delay due to this fuel cut. It does not happen at low rpm.
Heres more specific bike info now that you understand the idea...
Fuel Cut Eliminator Z1000/Ninja 1000 | Brock's Main Store
It was horrible on the 2011-2013 bikes. I understand not so bad in the 2014's.