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 time of seed application depends upon whether the grass is a cool-season or a warm-season species. Warm-season grasses established in temperate zones should be seeded in the spring as soon as soil temperatures are high enough to achieve germination.