how hard do you ride it?has it ever got hot or sucked water?fuels,mixes,jetting?too many variables.ballpark general opinion will prob recommend replacing at around 40-60hrs 125,60-80hrs 200,80-100hrs 250,100-120hrs 300.the smaller capacities rev higher and the tolerances are less forgiving.serious racers will prob be around 1/2 those hrs to keep engines fresh