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.
The BEST time to plant Bermuda Grass Seed is in late spring / early summer after soil temperatures are 65-70+ degrees or higher and all danger of freeze or frost is past.