gota 2015 with 3600 km on it.and have had this nagging shudder is the best why to describe it.that comes and than goes thane comes and than goes .....etc.when cruising. under 60 mph.over that not so much.it also backfires at shut down.(but that is common) mech says it the carb. because it dose not feel like tires out .because that would be all the time at all speeds.and everything is tight .is this a factory thing that i can fix. i know what i know about the issues with a single slug motor and the bike but this is new to me.thanks

Could be something in the charging system as well.  Check the battery for loose connections. These bikes vibrate so things can come loose.