Is this an HS6 or an HIF6?
On an HS6 put the carb top together with the needle sticking down, then put
the jet, jet sleeve, etc into the bottom around the needle, being careful
when tightening it up that the needle doesn't drag (work it up and down as
you sequentially tighten the plug in the bottom). When you get it good and
tight with the needle free, you should be ready to do the rest of the stuff.

On the HIF6 the jet is loose enough that this is rarely a problem. The
ones where it is really critical are the H4s where the jet actually goes
through some gasoline-proof packing so they have to be exactly centered.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma