Rx7Truett

I have a 1985 rx7 GS. I bought the car with the rats nest removed, which was done very poorly. I am in the process of re-running all the lines. I was wondering what this part is called? What is its funtion? and what should it be connected to? When I bought the car the carb was tuned to where idle was at 2k rpm. After re-tuning the carb idle was very poor until i found and plugged the vacuum leak where the arrow is pointing.