What is the difference between Beis Yosef meat and chicken vs Ashkanazi beef and chicken? Is it more stringent than ashkanazi all the time because they don’t rely on any sirchas of the lungs? Is there a difference in how Sefardim shecht chickens?
There is no difference in pricniple between how Ashkenazim and Sephardim perform their shechitah.
However, there is a difference in principle concerning checking lungs for sirchos, in that Sephardim cannot rely on the leniency of the Rema in permitting certain sirchos (by means of me’ichah).
The main differences between the various kashrus authorities is in how particular they are for checking the knife often, for not doing things too fast, for salting properly, and for all the other aspects that require care and attention. The differences are not between Sephardim and Ashkenazim, but between how much time and attention is given. This obviously makes a difference in price.
Note that for meat, Sephardi shechitah still does nikkur, which Ashkenazim do not do.