When using the single-vacuum distributor, the vacuum hose runs from the vacuum port on the left side of the carburetor to the vacuum canister on the distributor. In that case, the vacuum port on the rear of the carburetor must be plugged.
For most cool season grasses and for folks living in northern climates, the best time to plant grass is in late August, early September. Depending on exactly the climate you have and the type of grass seed you're planting.
Cool season grass germinates best when the soil temperatures are between 50 and 65 degrees F. These temperatures usually occur when the daytime air temperatures are between 60 and 75 degrees. High temperatures of summer can cause these plants to go dormant and thus planting during summer is asking for problems. Start planting your cool season grass seeds when the temperatures reach 75 and are dropping as fall / winter approaches. Or have reached 60 and are rising in the spring.