before you strip the carbs, have you checked the battery, charging system and have you checked to see the coils arnt croded on the terminals, are the plugs new, and are the caps and leads in good nic, if you didnt mess with the carbs while it was being rebuilt i would have thought it would run okay, unless youve got some dirt in there? stale fuel dosent help but if you drained it off it should be okay. someone else will be along to confirm if it sounds carb problem, but start with the above could save you some time if it turns out to be a rusty contact.