I had a Homelite that I had to do this mod on because on it's particular carb, the hole faced forward and was being pressurized by the airstream and causing the engine to lean out in flight. (On this one I was unable to just rotate the cover to a new position.) In other cases with cowls, it is sometimes necessary to add a tube and a hose running into the fuselage to sense static air because the air is pressurized in the cowling. (Note that this is not a "weep" hole; it is a air pressure sensing hole for the regulator.)

An uncowled Ryobi would not likely need this mod, as the carb is in the back and not in the airstream.

Good luck,
AV8TOR