Y'all is spoken with two syllables: ye-ALL. It can be heard up and down the east coast. It's just "ya" and "all" very close together.
Yall is spoken with one long syllable: YAAAWWL. It's very lazy sounding and only unashamed southerners use it.
Yall want to hear some banjo pickin?
Y'all want to roll in my Caprice?
Yall want to ride on my tractor?