You have to take the bowl off at the bottom with the float, and then bend the two flimsy metal prongs that the float pushes up dOWN a little bit so that the float closes them sooner.
Yes- I too have had problems with BOTH my builds- a 66 and a 50 with NT SPEED carbs suddenly, inexplicably leaking fuel- and quite a bit. So I'm not so high on them, but never used anything else but the old NT carb before that- which bogged down a bit on the 66 until I got a straight billet intake.
So now it seems there may be a fine line- the 50 build was doing it first- it took me a couple of times bending the metal prongs- and then it seemed that the motor was bogging on long stretches like it wasn't then getting ENOUGH gas- that sorta went away on it's own then
Then the 66 started leaking the same way- I bent ONCE, it leaked again at first, and I bounced the bike a few times in case the floatl was stick in the bowl-
it stopped leaking and hasn't since- but that motor never wants to idle well, unless it's very fast , And it bothers me that I have to choke the motor so much now- I never had to do that with the old standard NT carb and intake, but then again, it bogged down at speed.
One thing I found in the process was that the NT SPEED carbs have a float and bowl IDENTICAL to the old NT strandard I have around, though I think they advertised as a bigger bowl and float- anyway the jet and intake are a bit bigger.
May try some other carb some day, but doubt it. Don't want to spend money OR tinkler with it much these days- it just gets me around all over town.