ZX2-R Jerking

[dave63396]

Hi all when i went to start my bike it kicked over but made a loud clunk kinda sound then then it started after another attempt but i noticed the revs on the tachometer dropping up and down but not by much at all to really make it noticeable but as soon as i shifted into gear and go to take off, the bike constantly jerks the bike traveled 70 ks since the last fuel up so not sure if the fuel was contaminated does anyone else might know what may be causing this prob