Speed bleeders

I got some of these for my 76 vette so I could do a brake fluid change alone.
For some reason I cannot get the damned things to work. On the web,
they say 1/2 to 1 turn out. I get nothing. Then if I loosen it too much of course I get fluid all over the suspension from around the fitting.
What am I doing wrong? Is there a VERY finicky area of operation for these things?
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