[nmaineron]

On a correctly tuned machine, will the pilot screw turned all the way in, shut the bike down?

 

[Misters]

Yes. At the correct idle speed, the idle mixture screw allows a smooth idle and off idle performance, something you always go through while riding.
Engines that are not tuned well in this area have to be reved up (clutch & noise abuse) to get past the the low speed stumbling.

All the way in or out should produce poor idle performance

 

[Thermodyne]

Yep, if it don't, then either the seat is FUBAR'd. The float is set high. the enricher is leaking. Or the butterfly is set wrong and has uncovered the second transfer port.