When at normal idle, all 4 carb butterflys must be closed. There is a rod between carbs, and it is adjustable, usually with a screw mechanism on one carb. either carb (2 barrels) are ajar, that will feed extra air/fuel into the engine. You'll have to pull the airbox cover off to check this. All 4 must be closed and the cam roller must not touch the roller at idle. You should be able to slip a pc of paper between the cam and roller at idle.