Chicken with skin will produce a lot of moisture. So if your breasts had skin on them, and they were four large breasts, that is almost equivalent to 2 small chickens. A lot of moisture will be release, when that happens it takes a lot of energy (heat) to convert the water into a gas; this will keep your temperature down. If you do not have the vent open enough, most of the moisture will be trapped preventing the cabinet from heating up. The moisture will also worsen the texture of the skin. When smoking/cooking chicken with skin, you should have the vent 1/2 - 3/4 open when you start. After a while when most of the moisture has escaped, you can move the vent opening to a smaller setting. I generally start with the vent about 2/3 opened.
Also if you don't open the vent wide enough, a lot of that moisture will collect and flow out the bottom of the door. If you have the digital, you only need to worry about staining your deck, or floor. If you have the original, you need to worry about moisture seeping into the heating circuit. Some of us raise the front of the smoker about 1/4" to prevent any possibility of moisture flowing out of the front of the cabinet.
