HONDA city automatic-HELP!!!!

I have recently bought a used honda city automatic transmission i.e CVT. The car pick is normal but as i push the gas pedal for speed there is a kind of jerk and the car vibrates and it continues till i dont release the pedal and push it again. This doesnt happens every time but quite often. I m completely clueless. I just wanted to share this thing before i go to a mechanic. Is this some kind of a major problem or it would go away easily....Kindly advise what to do??