Yup the early Demons did have that trouble for sure. I am not a fan of Quick Fuel carbs, my son had one on his 409 and it ran so fat at idle it made your eyes water. Called QF and got the lean is mean speech, then I told the guy that a washed down cyl was just as bad and tell me why out of the box on a new carb that the throttle blade exposes almost .080 of the idle feed restrictor (t-slot). Nothing but mice sounds. If you want that carb to idle right you may have to add a restrictor in the main body, it's not too had to do otherwise get a Holley.