That's called the emulsion tube. It should be snug, not over tightened.
Solder the jet hole shut first. The easiest way is with a plumber's torch. Clean the jet as well as you can, then with a pair of needle nose pliers, heat the jet slowly. Apply a couple seconds of heat, pull the jet out of the flame, try melting solder to the jet. If it didn't melt, reapply a couple more seconds of heat. You will not want to use very much solder. Just enough to fill the hole. Apply from the bottom (the bottom, as it sits in the carb, don't solder upside down lol). Don't apply too much heat. You don't want to melt the jet.
I actually had luck with chucking the micro bit in a drill, but it's recommended to use a pin vise and drill by hand. Do not exert much pressure. You dont want to snap a bit. Once drilled, make sure you get all the shavings out, then reassemble it and go for a test ride. Continue until you get good power. Once it stops sputtering and 4 stroking, don't go any smaller. You want the jet as large as possible without affecting the performance. Too lean and you'll burn up the cylinder. Start with a 72 first, then work down.
Once you get it dialed in, change the spark plug (gapped at 0.025", and go for another ride. You may need to re-jet after changing the plug.