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.
You DO NOT WANT TO USE WEED KILLER ANYWHERE NEAR THE TIME YOU SOW GRASS SEED. The killer doesn't know the difference in grass seed that you want to grow and the weed seeds. There are two types of weeds. 1. Grassy weed (like crab grass) and 2. broadleaf weeds. The best time for killing the crabgrass is EARLY spring.