the only engine/trans performance upgrade to my sons 2006 ltz 50 ive done, was to remove the clutch restrictor ring which made a difference but it still was a pig up any kinda hill. i pulled off the exhaust to see if there was a restrictor washer at the head, no washer. i then pulled the baffle out of the pipe, BINGO, the baffle has tiny holes that are covered with a fine mesh screen that plug easily, i dont know how this thing actually breathed. heres what i did.

remove two 8 mm bolts that hold the baffle in at the end of the pipe and pull baffle out.

take a sawsall or hacksaw and cut the perforated end of the pipe with screen off (about 2 inches) and throw it in the trash

reinstall baffle locktite bolt

now that the exhaust can flow the bike has way more power, goes up hills, sounds louder/cooler but is not obnoxious, has some backpressure still, and the plug has good coloring so there is no jetting issues to address....................and the best part its FREE.