Most auto engines have a PVC valve mounted in the left valve cover with a vacuum hose from it to the large port on the carburetor. Some run a breather cap on the right side valve cover vented through the air breather base. Some run a breather cap with a filter. Do a search on on this site of crankcase ventilation. Make sure the valve covers have baffles where the breather caps are installed or oil splashes up the bottom on the bottom of the breathers.