The nt carb doesn't use an emulsion tube the hp carb does. What carb did you do this boring on? Carbs don't use a needle and jet with a emulsion tube they are 2 totally different style carbs.
Oh wow that's just dumb! He didn't do anything good there as in it will probably work worse than it did before. First when you create a choke point as he did there you get less fuel pulled up and through because the choke point reduced air speed/velocity then it has to be jetted richer just to get back to normal and will be much harder to tune correctly. Then I don't know what he measured 16.5mm in the inlet side with but he's full of s**t! On the NT carb the outer body isn't even 16mm on ether side so it's physically impossible to have 16.5 mm on the inlet or 16 on the outlet inside dia,here are some photo's showing the slide bore is only 15mm,the carb bore through the body is also only 15mm at best.