This is just a guess and is not based on any experience, but why not try opening up the second hole since it is below the fuel level and see how the engine likes it. You can always plug it back if the engine doesn't respond well.

And you may consider experimenting with the top hole as well once you get a sense of how the second hole affects things. As long as you do one thing at a time and keep track of what you do, you can always put it back the way it was.