Thanks a lot guys
. The answer was in front of my nose. I took off the rubber plug again and did a simple test: blow some air thorugh the breather hose and see if I could feel the air through the electric starter "hole". Actually the two are connected so as you say there's no pressure there...
I fitted the plug again, wich fits nice and tight (along with some gasket maker) and it's ready to go. I wanted to go to the woods but the rain is pouring again, maybe tomorrow
