Screw instead of a vent to the cylinder

[Wilmer]

Hello. I have a GasGas EC 125 05. And I saw that on the left side of the cylinder there is a little screw. But when I looked in the partlist of the bike a can see that there is going to be some sort of a vent. With a hose on. I wonder what that vent do and if I am going to replace the little screw with a knew original vent with a hose on? Will there be any difference? Will the bike go better or is it just better for the engine if there is the vent there. Here is a few pictures of my bike and someone else's bike with the vent.

My bike





How it is going to look

 

[Archibald]

My 300 had the screw in place of the vent when I got it. I replaced it with the original nipple/hose and ran the hose into the bash plate. It seems to run about the same, but there is significantly less spooge in the left exhaust valve cover.