The jet locking nut is used to centralize the jet on the needle. I have found that when the choke was too hard to pull the jets needed to be re-centered, but I've never had it work the other way.
Yes: That is true. The locking nut and cork washer assy. also seal the jet from leaking fuel. The trick is to center the jet and tighten the jet locking nut just enough to prevent fuel from leaking out but not so tight that the jet does not freely move up and down while choking. Not always easy to do. In the case of H-6 SU's the word is not "Choking" but "Fuel enrichment". Picky, Picky!
