ive had this problem for awhile and been too lazy to really address it. it only happens at low elevations, and no i do not have any cracks in my carb boots. on my way up to get to the real snow, it will do it untill i start gettin high up in elevations. im running a 400 main, and i have no idea how a person gets to the pilots with these carbs. and also, it will idle high, and if i hit the throttle quick, it will come down.