have a check, there is a rubber part where it goes in the carby, this can sometimes become loose, and when the cable goes taught to rev, it opens allowing in too much air, choking it out.
could also be the ratio, in which case you start it, check the carb for a small screw. play with it at the same time revving until the problem is gone. there may be two, one for idle and another allowing out more fuel. usually with most 2-stroke engines a safety net is to screw it all the way in and screw it back out 1.5 turns,