The little mixing tube (emulsion tube) goes in only one way.. One end of the tube opens up to a bigger hole.. this end of the tube is also slightly smaller in diameter.. this end goes upwards. (The other, bottom end has the cross-drilled hole near the end of the tube.)
Once the tube is seated up in the emulsion chamber, it's tip extends slightly into and can be seen in the carb's throat. The main jet seats it and holds the tube up in there.
Since you've got low speed trouble, something related to low speed running may be clogged.
There is an idle jet pressed into the carb body. It is under the flat-headed cover screw (below the idle speed screw). This jet's bore hole is very tiny. Find the thinnest strand of straight wire you can.. and poke it into the jet's bore to assure it's open. A single strand of throttle cable may be small enough. The bore hole is so small and deep in there that you may have trouble seeing it or getting the wire into it.
Although this jet is an "idle" jet, it does contribute fuel to part throttle operation untill about half throtle.. it and the whole idle pathway must be clean and clear.