Thunderbolt s3t sparkplugs missing

[Bills3t]

I am having an intermitent problem with my sparkplugs missing while I'm riding. I rebuilt the carburater in the Spring. I also changed the sparkplugs. When I'm ideling at a light the bike very rarely will have a miss and when the bike is at a constant rpm it will only miss once in a while. If someone could point me in the right direction so I can take care of this problem.