Motorcycle Repair: fuel petcock installation, vent hose, vacuum systems

Question
hey mike, i removed my fuel petcock on a 1976 flh.  i know that the large
double threaded nut has wasted threads, so i can't get things to stay
together.  with a new petcock, don't i start to thread the upper and lower
pieces at the same time as one is a reverse thread so they will each tighten up
at the same time?  also, what type or brand of petcock is best for my bike? it
is mostly stock except for the su hif carb.  with  this carb is there something  
that makes it so that the crankcase doesn't need the lower breather hose to
be open?  when i bought it that hose was plugged up with a clamped in bolt,  
and it always ran great. i'm reading things about vacuum systems vs. non-
vacuum,  but i believe the su carb draws fuel via vacuum somehow?  thanks
for helping me with a problem i had regarding the oil pump check ball.  i
removed the second ball (the old one) from the top of the spring and all is
just great.  thanks so much for the knowledge and expertise that you share
with everyone.  aloha,  chris zornes

Answer
Yes, you turn the nut on the petcock and it threads on both ends at the same time. There is really no best brand, unless you are running a high performance motor. Stick with a stock one.
Your bikes carb draws it vaccumn from the motor when the pistons go down. That pulls gas into the head. Are you sure the hose that is plugged is the vent hose? If it was plugged the motor would build pressure
Good luck and happy riding
Mike