My bike runs good tell i get to 4th gear and about 5,000 rpm it start to hesitate can anyone tell me what that can be

 

More info needed, do you have aftermarket anything (like pipe of Air filter)

 

i just got it and from what i know it has a k&n filter and a slip on it started doing it when i dropped it it fell on it's left side had frame slider so bike is not in bad shape just a few stratches besides that i don't think anything else was put on