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.
In climates with hot summers and cold winters, grass is ideally planted in the fall when the seeds will not easily dry up from the hot sun. Spring is the next-best choice. In areas where it is mildly warm all year, plant your grass anytime.