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.
That makes spring and early summer as the best time to plant warm season grass seed. Following germination make sure the new plants have adequate water during the remainder of the growing season. Most warm season grasses are typically planted with live plants instead of seed.