The gas porting provides a better ring seal. As you know the YS engines use crankcase pressure to run the regulator. If the ring seal leaks periodically while the engine is running and does not provide steady pressure in the case, the engine will surge while it is running due to fluctuating regulator pressure.
We used to build full size racing engines with this type mod and I decided to try it in the YS a couple of years ago. It has solved some nasty problems and as a benefit makes the ring last longer.

Dave