Be a little carefull about running with leaky exhaust, this can lean you out enough to burn the piston. See if you can find some way to clean the exhaust.
I have never tried this, but in the olden days when men were men and no chemicals ever did any harm, the recommended way of cleany a 2 cycle exhaust was to pug one end and fill the pipe with caustic soda solution. I believe that is quick lime or unslaked lime. It gets really hot when you add water. Ask your uncle if he heard of it and happy pedding.