I personally believe the slit is to disturb the forward flow of the side outlet to help not set bark on fire.Thanks for the correction mate, what slit are you referring to? I see one and 2 circledView attachment 1146551
By the way a Aussie ms660 has a from memory 13 or 14mm side outlet compared to the epa choked up American 8mm side outlet I believe but yeah is something like that.