Could be so many different things. Two strokes are basically one big semi-controlled air leak. If you have any extra air leaks like worn our crank seals, leaking crankcase halves, leaking fuel pump diaphragm, leaky seals at carb, etc you will have problems. Then add to that any fuel delivery problems and we haven't even talked about the ignition advance mechanism. I usually start with the fuel system first, make sure everything is clean, new fuel lines and filter, carb correctly adjusted as per service manual.
