My Nsr mc16 has starting running on one cylinder, top one only, it's the bottom one playing up, sometimes it's fine and then it'll just cut out and it'll only run in the top cylinder then all of a sudden it'll cut back in again and carry on running normally ?? I've changed plugs, cleaned out carbs and it's getting spark ok so don't really know what else to try ?

It's strange how it just cuts out and comes back in again about 10 seconds later ?
Any ideas guys ? Thanks