Crusing flat spot?

[superbike1300]

wondering if anyone has had this happen i notices in second gear between 38 to 40 mph and at 3900rpms ther seems to be a lag or flat spot almost a rais and drop of power while crusing not giving it throttle just holding it in the same position. ? ? ?

 

[frisbee]

 

[300Busa]

Every Busa I have been on has that same thing. Some people notice it, some don't.