I have the same problem, check list, coils , fuel tap ,breather for tank , carbs, split rubbers , plugs , air filter, compression, switches , disconected side stand switch , cleaned out tank,Ok prob forgot some stuff here but ive done everything I think possible , She runs goes for a bit then just stops 20 mins later she will run again. I thought i had it sussed when she rode ok for 40 miles , then the next day same thing again , stop start , If by any chance You solved this prob Please post cos i´m scratching my head here