Hi Ironbark,
I have to give up on this one, I cleaned the carby didn't help, fitted a new carby, didn't help so it has to be something internal and it is not worth going there. Only thing I haven't changed is the coil but the spark looks good on the timing light. I can't waste anymore time on it.
With the full cranks if you have any doubts, pull the heads off and have a look at the bores, that will give you some idea as to their condition