Might not be a carby problem. I'd take off the carby and muffler,get a torch and look at the bore. Especially on the muffler side,see if it has makes in the bore. With what you can see of the rings see if their is any cracks in the rings. Sounds like one I had a few years ago would start if I gave it fuel but wouldn't run. Turned out it had scratchs in the bore and both rings where cracked.
