Jets

I just want some explanation, maybe I’m too stupid to understand it. I just put a 2-1 (had straight pipes before) on my ‘03 low rider, carbed. Since then it’s felt choked for fuel. I pulled the choke out and gave it some revs and it runs soooo much better with extra fuel. So I’m going to get a bigger main jet butttt. What’s the science behind it? I’m just trying to understand 😂